Add ALTS code to grpc/core

51 files changed, 8792 insertions, 0 deletions

diff --git a/src/core/tsi/alts/crypt/aes_gcm.cc b/src/core/tsi/alts/crypt/aes_gcm.cc
new file mode 100644
index 0000000000..02b1ac4492
--- /dev/null
+++ b/src/core/tsi/alts/crypt/aes_gcm.cc
@@ -0,0 +1,687 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/crypt/gsec.h"
+
+#include <openssl/bio.h>
+#include <openssl/buffer.h>
+#include <openssl/err.h>
+#include <openssl/evp.h>
+#include <openssl/hmac.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+
+constexpr size_t kKdfKeyLen = 32;
+constexpr size_t kKdfCounterLen = 6;
+constexpr size_t kKdfCounterOffset = 2;
+constexpr size_t kRekeyAeadKeyLen = kAes128GcmKeyLength;
+
+/* Struct for additional data required if rekeying is enabled. */
+struct gsec_aes_gcm_aead_rekey_data {
+  uint8_t kdf_counter[kKdfCounterLen];
+  uint8_t nonce_mask[kAesGcmNonceLength];
+};
+
+/* Main struct for AES_GCM crypter interface. */
+struct gsec_aes_gcm_aead_crypter {
+  gsec_aead_crypter crypter;
+  size_t key_length;
+  size_t nonce_length;
+  size_t tag_length;
+  uint8_t* key;
+  gsec_aes_gcm_aead_rekey_data* rekey_data;
+  EVP_CIPHER_CTX* ctx;
+};
+
+static char* aes_gcm_get_openssl_errors() {
+  BIO* bio = BIO_new(BIO_s_mem());
+  ERR_print_errors(bio);
+  BUF_MEM* mem = nullptr;
+  char* error_msg = nullptr;
+  BIO_get_mem_ptr(bio, &mem);
+  if (mem != nullptr) {
+    error_msg = static_cast<char*>(gpr_malloc(mem->length + 1));
+    memcpy(error_msg, mem->data, mem->length);
+    error_msg[mem->length] = '\0';
+  }
+  BIO_free_all(bio);
+  return error_msg;
+}
+
+static void aes_gcm_format_errors(const char* error_msg, char** error_details) {
+  if (error_details == nullptr) {
+    return;
+  }
+  unsigned long error = ERR_get_error();
+  if (error == 0 && error_msg != nullptr) {
+    *error_details = static_cast<char*>(gpr_malloc(strlen(error_msg) + 1));
+    memcpy(*error_details, error_msg, strlen(error_msg) + 1);
+    return;
+  }
+  char* openssl_errors = aes_gcm_get_openssl_errors();
+  if (openssl_errors != nullptr && error_msg != nullptr) {
+    size_t len = strlen(error_msg) + strlen(openssl_errors) + 2; /* ", " */
+    *error_details = static_cast<char*>(gpr_malloc(len + 1));
+    snprintf(*error_details, len + 1, "%s, %s", error_msg, openssl_errors);
+    gpr_free(openssl_errors);
+  }
+}
+
+static grpc_status_code gsec_aes_gcm_aead_crypter_max_ciphertext_and_tag_length(
+    const gsec_aead_crypter* crypter, size_t plaintext_length,
+    size_t* max_ciphertext_and_tag_length, char** error_details) {
+  if (max_ciphertext_and_tag_length == nullptr) {
+    aes_gcm_format_errors("max_ciphertext_and_tag_length is nullptr.",
+                          error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      reinterpret_cast<gsec_aes_gcm_aead_crypter*>(
+          const_cast<gsec_aead_crypter*>(crypter));
+  *max_ciphertext_and_tag_length =
+      plaintext_length + aes_gcm_crypter->tag_length;
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code gsec_aes_gcm_aead_crypter_max_plaintext_length(
+    const gsec_aead_crypter* crypter, size_t ciphertext_and_tag_length,
+    size_t* max_plaintext_length, char** error_details) {
+  if (max_plaintext_length == nullptr) {
+    aes_gcm_format_errors("max_plaintext_length is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      reinterpret_cast<gsec_aes_gcm_aead_crypter*>(
+          const_cast<gsec_aead_crypter*>(crypter));
+  if (ciphertext_and_tag_length < aes_gcm_crypter->tag_length) {
+    *max_plaintext_length = 0;
+    aes_gcm_format_errors(
+        "ciphertext_and_tag_length is smaller than tag_length.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  *max_plaintext_length =
+      ciphertext_and_tag_length - aes_gcm_crypter->tag_length;
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code gsec_aes_gcm_aead_crypter_nonce_length(
+    const gsec_aead_crypter* crypter, size_t* nonce_length,
+    char** error_details) {
+  if (nonce_length == nullptr) {
+    aes_gcm_format_errors("nonce_length is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      reinterpret_cast<gsec_aes_gcm_aead_crypter*>(
+          const_cast<gsec_aead_crypter*>(crypter));
+  *nonce_length = aes_gcm_crypter->nonce_length;
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code gsec_aes_gcm_aead_crypter_key_length(
+    const gsec_aead_crypter* crypter, size_t* key_length,
+    char** error_details) {
+  if (key_length == nullptr) {
+    aes_gcm_format_errors("key_length is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      reinterpret_cast<gsec_aes_gcm_aead_crypter*>(
+          const_cast<gsec_aead_crypter*>(crypter));
+  *key_length = aes_gcm_crypter->key_length;
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code gsec_aes_gcm_aead_crypter_tag_length(
+    const gsec_aead_crypter* crypter, size_t* tag_length,
+    char** error_details) {
+  if (tag_length == nullptr) {
+    aes_gcm_format_errors("tag_length is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      reinterpret_cast<gsec_aes_gcm_aead_crypter*>(
+          const_cast<gsec_aead_crypter*>(crypter));
+  *tag_length = aes_gcm_crypter->tag_length;
+  return GRPC_STATUS_OK;
+}
+
+static void aes_gcm_mask_nonce(uint8_t* dst, const uint8_t* nonce,
+                               const uint8_t* mask) {
+  uint64_t mask1;
+  uint32_t mask2;
+  memcpy(&mask1, mask, sizeof(mask1));
+  memcpy(&mask2, mask + sizeof(mask1), sizeof(mask2));
+  uint64_t nonce1;
+  uint32_t nonce2;
+  memcpy(&nonce1, nonce, sizeof(nonce1));
+  memcpy(&nonce2, nonce + sizeof(nonce1), sizeof(nonce2));
+  nonce1 ^= mask1;
+  nonce2 ^= mask2;
+  memcpy(dst, &nonce1, sizeof(nonce1));
+  memcpy(dst + sizeof(nonce1), &nonce2, sizeof(nonce2));
+}
+
+static grpc_status_code aes_gcm_derive_aead_key(uint8_t* dst,
+                                                const uint8_t* kdf_key,
+                                                const uint8_t* kdf_counter) {
+  unsigned char buf[EVP_MAX_MD_SIZE];
+  unsigned char ctr = 1;
+#if OPENSSL_VERSION_NUMBER < 0x10100000L
+  HMAC_CTX hmac;
+  HMAC_CTX_init(&hmac);
+  if (!HMAC_Init_ex(&hmac, kdf_key, kKdfKeyLen, EVP_sha256(), nullptr) ||
+      !HMAC_Update(&hmac, kdf_counter, kKdfCounterLen) ||
+      !HMAC_Update(&hmac, &ctr, 1) || !HMAC_Final(&hmac, buf, nullptr)) {
+    HMAC_CTX_cleanup(&hmac);
+    return GRPC_STATUS_INTERNAL;
+  }
+  HMAC_CTX_cleanup(&hmac);
+#else
+  HMAC_CTX* hmac = HMAC_CTX_new();
+  if (hmac == nullptr) {
+    return GRPC_STATUS_INTERNAL;
+  }
+  if (!HMAC_Init_ex(hmac, kdf_key, kKdfKeyLen, EVP_sha256(), nullptr) ||
+      !HMAC_Update(hmac, kdf_counter, kKdfCounterLen) ||
+      !HMAC_Update(hmac, &ctr, 1) || !HMAC_Final(hmac, buf, nullptr)) {
+    HMAC_CTX_free(hmac);
+    return GRPC_STATUS_INTERNAL;
+  }
+  HMAC_CTX_free(hmac);
+#endif
+  memcpy(dst, buf, kRekeyAeadKeyLen);
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code aes_gcm_rekey_if_required(
+    gsec_aes_gcm_aead_crypter* aes_gcm_crypter, const uint8_t* nonce,
+    char** error_details) {
+  // If rekey_data is nullptr, then rekeying is not supported and not required.
+  // If bytes 2-7 of kdf_counter differ from the (per message) nonce, then the
+  // encryption key is recomputed from a new kdf_counter to ensure that we don't
+  // encrypt more than 2^16 messages per encryption key (in each direction).
+  if (aes_gcm_crypter->rekey_data == nullptr ||
+      memcmp(aes_gcm_crypter->rekey_data->kdf_counter,
+             nonce + kKdfCounterOffset, kKdfCounterLen) == 0) {
+    return GRPC_STATUS_OK;
+  }
+  memcpy(aes_gcm_crypter->rekey_data->kdf_counter, nonce + kKdfCounterOffset,
+         kKdfCounterLen);
+  uint8_t aead_key[kRekeyAeadKeyLen];
+  if (aes_gcm_derive_aead_key(aead_key, aes_gcm_crypter->key,
+                              aes_gcm_crypter->rekey_data->kdf_counter) !=
+      GRPC_STATUS_OK) {
+    aes_gcm_format_errors("Rekeying failed in key derivation.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  if (!EVP_DecryptInit_ex(aes_gcm_crypter->ctx, nullptr, nullptr, aead_key,
+                          nullptr)) {
+    aes_gcm_format_errors("Rekeying failed in context update.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code gsec_aes_gcm_aead_crypter_encrypt_iovec(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const struct iovec* aad_vec, size_t aad_vec_length,
+    const struct iovec* plaintext_vec, size_t plaintext_vec_length,
+    struct iovec ciphertext_vec, size_t* ciphertext_bytes_written,
+    char** error_details) {
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      reinterpret_cast<gsec_aes_gcm_aead_crypter*>(crypter);
+  // Input checks
+  if (nonce == nullptr) {
+    aes_gcm_format_errors("Nonce buffer is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (kAesGcmNonceLength != nonce_length) {
+    aes_gcm_format_errors("Nonce buffer has the wrong length.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (aad_vec_length > 0 && aad_vec == nullptr) {
+    aes_gcm_format_errors("Non-zero aad_vec_length but aad_vec is nullptr.",
+                          error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (plaintext_vec_length > 0 && plaintext_vec == nullptr) {
+    aes_gcm_format_errors(
+        "Non-zero plaintext_vec_length but plaintext_vec is nullptr.",
+        error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (ciphertext_bytes_written == nullptr) {
+    aes_gcm_format_errors("bytes_written is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  *ciphertext_bytes_written = 0;
+  // rekey if required
+  if (aes_gcm_rekey_if_required(aes_gcm_crypter, nonce, error_details) !=
+      GRPC_STATUS_OK) {
+    return GRPC_STATUS_INTERNAL;
+  }
+  // mask nonce if required
+  const uint8_t* nonce_aead = nonce;
+  uint8_t nonce_masked[kAesGcmNonceLength];
+  if (aes_gcm_crypter->rekey_data != nullptr) {
+    aes_gcm_mask_nonce(nonce_masked, aes_gcm_crypter->rekey_data->nonce_mask,
+                       nonce);
+    nonce_aead = nonce_masked;
+  }
+  // init openssl context
+  if (!EVP_EncryptInit_ex(aes_gcm_crypter->ctx, nullptr, nullptr, nullptr,
+                          nonce_aead)) {
+    aes_gcm_format_errors("Initializing nonce failed", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  // process aad
+  size_t i;
+  for (i = 0; i < aad_vec_length; i++) {
+    const uint8_t* aad = static_cast<uint8_t*>(aad_vec[i].iov_base);
+    size_t aad_length = aad_vec[i].iov_len;
+    if (aad_length == 0) {
+      continue;
+    }
+    size_t aad_bytes_read = 0;
+    if (aad == nullptr) {
+      aes_gcm_format_errors("aad is nullptr.", error_details);
+      return GRPC_STATUS_INVALID_ARGUMENT;
+    }
+    if (!EVP_EncryptUpdate(aes_gcm_crypter->ctx, nullptr,
+                           reinterpret_cast<int*>(&aad_bytes_read), aad,
+                           static_cast<int>(aad_length)) ||
+        aad_bytes_read != aad_length) {
+      aes_gcm_format_errors("Setting authenticated associated data failed",
+                            error_details);
+      return GRPC_STATUS_INTERNAL;
+    }
+  }
+  uint8_t* ciphertext = static_cast<uint8_t*>(ciphertext_vec.iov_base);
+  size_t ciphertext_length = ciphertext_vec.iov_len;
+  if (ciphertext == nullptr) {
+    aes_gcm_format_errors("ciphertext is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  // process plaintext
+  for (i = 0; i < plaintext_vec_length; i++) {
+    const uint8_t* plaintext = static_cast<uint8_t*>(plaintext_vec[i].iov_base);
+    size_t plaintext_length = plaintext_vec[i].iov_len;
+    if (plaintext == nullptr) {
+      if (plaintext_length == 0) {
+        continue;
+      }
+      aes_gcm_format_errors("plaintext is nullptr.", error_details);
+      return GRPC_STATUS_INVALID_ARGUMENT;
+    }
+    if (ciphertext_length < plaintext_length) {
+      aes_gcm_format_errors(
+          "ciphertext is not large enough to hold the result.", error_details);
+      return GRPC_STATUS_INVALID_ARGUMENT;
+    }
+    int bytes_written = 0;
+    int bytes_to_write = static_cast<int>(plaintext_length);
+    if (!EVP_EncryptUpdate(aes_gcm_crypter->ctx, ciphertext, &bytes_written,
+                           plaintext, bytes_to_write)) {
+      aes_gcm_format_errors("Encrypting plaintext failed.", error_details);
+      return GRPC_STATUS_INTERNAL;
+    }
+    if (bytes_written > bytes_to_write) {
+      aes_gcm_format_errors("More bytes written than expected.", error_details);
+      return GRPC_STATUS_INTERNAL;
+    }
+    ciphertext += bytes_written;
+    ciphertext_length -= bytes_written;
+  }
+  int bytes_written_temp = 0;
+  if (!EVP_EncryptFinal_ex(aes_gcm_crypter->ctx, nullptr,
+                           &bytes_written_temp)) {
+    aes_gcm_format_errors("Finalizing encryption failed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  if (bytes_written_temp != 0) {
+    aes_gcm_format_errors("Openssl wrote some unexpected bytes.",
+                          error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  if (ciphertext_length < kAesGcmTagLength) {
+    aes_gcm_format_errors("ciphertext is too small to hold a tag.",
+                          error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+
+  if (!EVP_CIPHER_CTX_ctrl(aes_gcm_crypter->ctx, EVP_CTRL_GCM_GET_TAG,
+                           kAesGcmTagLength, ciphertext)) {
+    aes_gcm_format_errors("Writing tag failed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  ciphertext += kAesGcmTagLength;
+  ciphertext_length -= kAesGcmTagLength;
+  *ciphertext_bytes_written = ciphertext_vec.iov_len - ciphertext_length;
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code gsec_aes_gcm_aead_crypter_decrypt_iovec(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const struct iovec* aad_vec, size_t aad_vec_length,
+    const struct iovec* ciphertext_vec, size_t ciphertext_vec_length,
+    struct iovec plaintext_vec, size_t* plaintext_bytes_written,
+    char** error_details) {
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      reinterpret_cast<gsec_aes_gcm_aead_crypter*>(
+          const_cast<gsec_aead_crypter*>(crypter));
+  if (nonce == nullptr) {
+    aes_gcm_format_errors("Nonce buffer is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (kAesGcmNonceLength != nonce_length) {
+    aes_gcm_format_errors("Nonce buffer has the wrong length.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (aad_vec_length > 0 && aad_vec == nullptr) {
+    aes_gcm_format_errors("Non-zero aad_vec_length but aad_vec is nullptr.",
+                          error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (ciphertext_vec_length > 0 && ciphertext_vec == nullptr) {
+    aes_gcm_format_errors(
+        "Non-zero plaintext_vec_length but plaintext_vec is nullptr.",
+        error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  // Compute the total length so we can ensure we don't pass the tag into
+  // EVP_decrypt.
+  size_t total_ciphertext_length = 0;
+  size_t i;
+  for (i = 0; i < ciphertext_vec_length; i++) {
+    total_ciphertext_length += ciphertext_vec[i].iov_len;
+  }
+  if (total_ciphertext_length < kAesGcmTagLength) {
+    aes_gcm_format_errors("ciphertext is too small to hold a tag.",
+                          error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (plaintext_bytes_written == nullptr) {
+    aes_gcm_format_errors("bytes_written is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  *plaintext_bytes_written = 0;
+  // rekey if required
+  if (aes_gcm_rekey_if_required(aes_gcm_crypter, nonce, error_details) !=
+      GRPC_STATUS_OK) {
+    aes_gcm_format_errors("Rekeying failed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  // mask nonce if required
+  const uint8_t* nonce_aead = nonce;
+  uint8_t nonce_masked[kAesGcmNonceLength];
+  if (aes_gcm_crypter->rekey_data != nullptr) {
+    aes_gcm_mask_nonce(nonce_masked, aes_gcm_crypter->rekey_data->nonce_mask,
+                       nonce);
+    nonce_aead = nonce_masked;
+  }
+  // init openssl context
+  if (!EVP_DecryptInit_ex(aes_gcm_crypter->ctx, nullptr, nullptr, nullptr,
+                          nonce_aead)) {
+    aes_gcm_format_errors("Initializing nonce failed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  // process aad
+  for (i = 0; i < aad_vec_length; i++) {
+    const uint8_t* aad = static_cast<uint8_t*>(aad_vec[i].iov_base);
+    size_t aad_length = aad_vec[i].iov_len;
+    if (aad_length == 0) {
+      continue;
+    }
+    size_t aad_bytes_read = 0;
+    if (aad == nullptr) {
+      aes_gcm_format_errors("aad is nullptr.", error_details);
+      return GRPC_STATUS_INVALID_ARGUMENT;
+    }
+    if (!EVP_DecryptUpdate(aes_gcm_crypter->ctx, nullptr,
+                           reinterpret_cast<int*>(&aad_bytes_read), aad,
+                           static_cast<int>(aad_length)) ||
+        aad_bytes_read != aad_length) {
+      aes_gcm_format_errors("Setting authenticated associated data failed.",
+                            error_details);
+      return GRPC_STATUS_INTERNAL;
+    }
+  }
+  // process ciphertext
+  uint8_t* plaintext = static_cast<uint8_t*>(plaintext_vec.iov_base);
+  size_t plaintext_length = plaintext_vec.iov_len;
+  if (plaintext_length > 0 && plaintext == nullptr) {
+    aes_gcm_format_errors(
+        "plaintext is nullptr, but plaintext_length is positive.",
+        error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  const uint8_t* ciphertext = nullptr;
+  size_t ciphertext_length = 0;
+  for (i = 0;
+       i < ciphertext_vec_length && total_ciphertext_length > kAesGcmTagLength;
+       i++) {
+    ciphertext = static_cast<uint8_t*>(ciphertext_vec[i].iov_base);
+    ciphertext_length = ciphertext_vec[i].iov_len;
+    if (ciphertext == nullptr) {
+      if (ciphertext_length == 0) {
+        continue;
+      }
+      aes_gcm_format_errors("ciphertext is nullptr.", error_details);
+      memset(plaintext_vec.iov_base, 0x00, plaintext_vec.iov_len);
+      return GRPC_STATUS_INVALID_ARGUMENT;
+    }
+    size_t bytes_written = 0;
+    size_t bytes_to_write = ciphertext_length;
+    // Don't include the tag
+    if (bytes_to_write > total_ciphertext_length - kAesGcmTagLength) {
+      bytes_to_write = total_ciphertext_length - kAesGcmTagLength;
+    }
+    if (plaintext_length < bytes_to_write) {
+      aes_gcm_format_errors(
+          "Not enough plaintext buffer to hold encrypted ciphertext.",
+          error_details);
+      return GRPC_STATUS_INVALID_ARGUMENT;
+    }
+    if (!EVP_DecryptUpdate(aes_gcm_crypter->ctx, plaintext,
+                           reinterpret_cast<int*>(&bytes_written), ciphertext,
+                           static_cast<int>(bytes_to_write))) {
+      aes_gcm_format_errors("Decrypting ciphertext failed.", error_details);
+      memset(plaintext_vec.iov_base, 0x00, plaintext_vec.iov_len);
+      return GRPC_STATUS_INTERNAL;
+    }
+    if (bytes_written > ciphertext_length) {
+      aes_gcm_format_errors("More bytes written than expected.", error_details);
+      memset(plaintext_vec.iov_base, 0x00, plaintext_vec.iov_len);
+      return GRPC_STATUS_INTERNAL;
+    }
+    ciphertext += bytes_written;
+    ciphertext_length -= bytes_written;
+    total_ciphertext_length -= bytes_written;
+    plaintext += bytes_written;
+    plaintext_length -= bytes_written;
+  }
+  if (total_ciphertext_length > kAesGcmTagLength) {
+    aes_gcm_format_errors(
+        "Not enough plaintext buffer to hold encrypted ciphertext.",
+        error_details);
+    memset(plaintext_vec.iov_base, 0x00, plaintext_vec.iov_len);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  uint8_t tag[kAesGcmTagLength];
+  uint8_t* tag_tmp = tag;
+  if (ciphertext_length > 0) {
+    memcpy(tag_tmp, ciphertext, ciphertext_length);
+    tag_tmp += ciphertext_length;
+    total_ciphertext_length -= ciphertext_length;
+  }
+  for (; i < ciphertext_vec_length; i++) {
+    ciphertext = static_cast<uint8_t*>(ciphertext_vec[i].iov_base);
+    ciphertext_length = ciphertext_vec[i].iov_len;
+    if (ciphertext == nullptr) {
+      if (ciphertext_length == 0) {
+        continue;
+      }
+      aes_gcm_format_errors("ciphertext is nullptr.", error_details);
+      memset(plaintext_vec.iov_base, 0x00, plaintext_vec.iov_len);
+      return GRPC_STATUS_INVALID_ARGUMENT;
+    }
+    memcpy(tag_tmp, ciphertext, ciphertext_length);
+    tag_tmp += ciphertext_length;
+    total_ciphertext_length -= ciphertext_length;
+  }
+  if (!EVP_CIPHER_CTX_ctrl(aes_gcm_crypter->ctx, EVP_CTRL_GCM_SET_TAG,
+                           kAesGcmTagLength, reinterpret_cast<void*>(tag))) {
+    aes_gcm_format_errors("Setting tag failed.", error_details);
+    memset(plaintext_vec.iov_base, 0x00, plaintext_vec.iov_len);
+    return GRPC_STATUS_INTERNAL;
+  }
+  int bytes_written_temp = 0;
+  if (!EVP_DecryptFinal_ex(aes_gcm_crypter->ctx, nullptr,
+                           &bytes_written_temp)) {
+    aes_gcm_format_errors("Checking tag failed.", error_details);
+    memset(plaintext_vec.iov_base, 0x00, plaintext_vec.iov_len);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  if (bytes_written_temp != 0) {
+    aes_gcm_format_errors("Openssl wrote some unexpected bytes.",
+                          error_details);
+    memset(plaintext_vec.iov_base, 0x00, plaintext_vec.iov_len);
+    return GRPC_STATUS_INTERNAL;
+  }
+  *plaintext_bytes_written = plaintext_vec.iov_len - plaintext_length;
+  return GRPC_STATUS_OK;
+}
+
+static void gsec_aes_gcm_aead_crypter_destroy(gsec_aead_crypter* crypter) {
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      reinterpret_cast<gsec_aes_gcm_aead_crypter*>(
+          const_cast<gsec_aead_crypter*>(crypter));
+  gpr_free(aes_gcm_crypter->key);
+  gpr_free(aes_gcm_crypter->rekey_data);
+  EVP_CIPHER_CTX_free(aes_gcm_crypter->ctx);
+}
+
+static const gsec_aead_crypter_vtable vtable = {
+    gsec_aes_gcm_aead_crypter_encrypt_iovec,
+    gsec_aes_gcm_aead_crypter_decrypt_iovec,
+    gsec_aes_gcm_aead_crypter_max_ciphertext_and_tag_length,
+    gsec_aes_gcm_aead_crypter_max_plaintext_length,
+    gsec_aes_gcm_aead_crypter_nonce_length,
+    gsec_aes_gcm_aead_crypter_key_length,
+    gsec_aes_gcm_aead_crypter_tag_length,
+    gsec_aes_gcm_aead_crypter_destroy};
+
+static grpc_status_code aes_gcm_new_evp_cipher_ctx(
+    gsec_aes_gcm_aead_crypter* aes_gcm_crypter, char** error_details) {
+  const EVP_CIPHER* cipher = nullptr;
+  bool is_rekey = aes_gcm_crypter->rekey_data != nullptr;
+  switch (is_rekey ? kRekeyAeadKeyLen : aes_gcm_crypter->key_length) {
+    case kAes128GcmKeyLength:
+      cipher = EVP_aes_128_gcm();
+      break;
+    case kAes256GcmKeyLength:
+      cipher = EVP_aes_256_gcm();
+      break;
+  }
+  const uint8_t* aead_key = aes_gcm_crypter->key;
+  uint8_t aead_key_rekey[kRekeyAeadKeyLen];
+  if (is_rekey) {
+    if (aes_gcm_derive_aead_key(aead_key_rekey, aes_gcm_crypter->key,
+                                aes_gcm_crypter->rekey_data->kdf_counter) !=
+        GRPC_STATUS_OK) {
+      aes_gcm_format_errors("Deriving key failed.", error_details);
+      return GRPC_STATUS_INTERNAL;
+    }
+    aead_key = aead_key_rekey;
+  }
+  if (!EVP_DecryptInit_ex(aes_gcm_crypter->ctx, cipher, nullptr, aead_key,
+                          nullptr)) {
+    aes_gcm_format_errors("Setting key failed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  if (!EVP_CIPHER_CTX_ctrl(aes_gcm_crypter->ctx, EVP_CTRL_GCM_SET_IVLEN,
+                           static_cast<int>(aes_gcm_crypter->nonce_length),
+                           nullptr)) {
+    aes_gcm_format_errors("Setting nonce length failed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  return GRPC_STATUS_OK;
+}
+
+grpc_status_code gsec_aes_gcm_aead_crypter_create(const uint8_t* key,
+                                                  size_t key_length,
+                                                  size_t nonce_length,
+                                                  size_t tag_length, bool rekey,
+                                                  gsec_aead_crypter** crypter,
+                                                  char** error_details) {
+  if (key == nullptr) {
+    aes_gcm_format_errors("key is nullptr.", error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  if (crypter == nullptr) {
+    aes_gcm_format_errors("crypter is nullptr.", error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  *crypter = nullptr;
+  if ((rekey && key_length != kAes128GcmRekeyKeyLength) ||
+      (!rekey && key_length != kAes128GcmKeyLength &&
+       key_length != kAes256GcmKeyLength) ||
+      (tag_length != kAesGcmTagLength) ||
+      (nonce_length != kAesGcmNonceLength)) {
+    aes_gcm_format_errors(
+        "Invalid key and/or nonce and/or tag length are provided at AEAD "
+        "crypter instance construction time.",
+        error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  gsec_aes_gcm_aead_crypter* aes_gcm_crypter =
+      static_cast<gsec_aes_gcm_aead_crypter*>(
+          gpr_malloc(sizeof(gsec_aes_gcm_aead_crypter)));
+  aes_gcm_crypter->crypter.vtable = &vtable;
+  aes_gcm_crypter->nonce_length = nonce_length;
+  aes_gcm_crypter->tag_length = tag_length;
+  if (rekey) {
+    aes_gcm_crypter->key_length = kKdfKeyLen;
+    aes_gcm_crypter->rekey_data = static_cast<gsec_aes_gcm_aead_rekey_data*>(
+        gpr_malloc(sizeof(gsec_aes_gcm_aead_rekey_data)));
+    memcpy(aes_gcm_crypter->rekey_data->nonce_mask, key + kKdfKeyLen,
+           kAesGcmNonceLength);
+    // Set kdf_counter to all-zero for initial key derivation.
+    memset(aes_gcm_crypter->rekey_data->kdf_counter, 0, kKdfCounterLen);
+  } else {
+    aes_gcm_crypter->key_length = key_length;
+    aes_gcm_crypter->rekey_data = nullptr;
+  }
+  aes_gcm_crypter->key =
+      static_cast<uint8_t*>(gpr_malloc(aes_gcm_crypter->key_length));
+  memcpy(aes_gcm_crypter->key, key, aes_gcm_crypter->key_length);
+  aes_gcm_crypter->ctx = EVP_CIPHER_CTX_new();
+  grpc_status_code status =
+      aes_gcm_new_evp_cipher_ctx(aes_gcm_crypter, error_details);
+  if (status != GRPC_STATUS_OK) {
+    gsec_aes_gcm_aead_crypter_destroy(&aes_gcm_crypter->crypter);
+    gpr_free(aes_gcm_crypter);
+    return status;
+  }
+  *crypter = &aes_gcm_crypter->crypter;
+  return GRPC_STATUS_OK;
+}
diff --git a/src/core/tsi/alts/crypt/gsec.cc b/src/core/tsi/alts/crypt/gsec.cc
new file mode 100644
index 0000000000..6236591a97
--- /dev/null
+++ b/src/core/tsi/alts/crypt/gsec.cc
@@ -0,0 +1,189 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/crypt/gsec.h"
+
+#include <stdio.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+
+static const char vtable_error_msg[] =
+    "crypter or crypter->vtable has not been initialized properly";
+
+static void maybe_copy_error_msg(const char* src, char** dst) {
+  if (dst != nullptr && src != nullptr) {
+    *dst = static_cast<char*>(gpr_malloc(strlen(src) + 1));
+    memcpy(*dst, src, strlen(src) + 1);
+  }
+}
+
+grpc_status_code gsec_aead_crypter_encrypt(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const uint8_t* aad, size_t aad_length, const uint8_t* plaintext,
+    size_t plaintext_length, uint8_t* ciphertext_and_tag,
+    size_t ciphertext_and_tag_length, size_t* bytes_written,
+    char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->encrypt_iovec != nullptr) {
+    struct iovec aad_vec = {(void*)aad, aad_length};
+    struct iovec plaintext_vec = {(void*)plaintext, plaintext_length};
+    struct iovec ciphertext_vec = {ciphertext_and_tag,
+                                   ciphertext_and_tag_length};
+    return crypter->vtable->encrypt_iovec(
+        crypter, nonce, nonce_length, &aad_vec, 1, &plaintext_vec, 1,
+        ciphertext_vec, bytes_written, error_details);
+  }
+  /* An error occurred. */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+grpc_status_code gsec_aead_crypter_encrypt_iovec(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const struct iovec* aad_vec, size_t aad_vec_length,
+    const struct iovec* plaintext_vec, size_t plaintext_vec_length,
+    struct iovec ciphertext_vec, size_t* ciphertext_bytes_written,
+    char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->encrypt_iovec != nullptr) {
+    return crypter->vtable->encrypt_iovec(
+        crypter, nonce, nonce_length, aad_vec, aad_vec_length, plaintext_vec,
+        plaintext_vec_length, ciphertext_vec, ciphertext_bytes_written,
+        error_details);
+  }
+  /* An error occurred. */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+grpc_status_code gsec_aead_crypter_decrypt(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const uint8_t* aad, size_t aad_length, const uint8_t* ciphertext_and_tag,
+    size_t ciphertext_and_tag_length, uint8_t* plaintext,
+    size_t plaintext_length, size_t* bytes_written, char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->decrypt_iovec != nullptr) {
+    struct iovec aad_vec = {(void*)aad, aad_length};
+    struct iovec ciphertext_vec = {(void*)ciphertext_and_tag,
+                                   ciphertext_and_tag_length};
+    struct iovec plaintext_vec = {plaintext, plaintext_length};
+    return crypter->vtable->decrypt_iovec(
+        crypter, nonce, nonce_length, &aad_vec, 1, &ciphertext_vec, 1,
+        plaintext_vec, bytes_written, error_details);
+  }
+  /* An error occurred. */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+grpc_status_code gsec_aead_crypter_decrypt_iovec(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const struct iovec* aad_vec, size_t aad_vec_length,
+    const struct iovec* ciphertext_vec, size_t ciphertext_vec_length,
+    struct iovec plaintext_vec, size_t* plaintext_bytes_written,
+    char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->encrypt_iovec != nullptr) {
+    return crypter->vtable->decrypt_iovec(
+        crypter, nonce, nonce_length, aad_vec, aad_vec_length, ciphertext_vec,
+        ciphertext_vec_length, plaintext_vec, plaintext_bytes_written,
+        error_details);
+  }
+  /* An error occurred. */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+grpc_status_code gsec_aead_crypter_max_ciphertext_and_tag_length(
+    const gsec_aead_crypter* crypter, size_t plaintext_length,
+    size_t* max_ciphertext_and_tag_length_to_return, char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->max_ciphertext_and_tag_length != nullptr) {
+    return crypter->vtable->max_ciphertext_and_tag_length(
+        crypter, plaintext_length, max_ciphertext_and_tag_length_to_return,
+        error_details);
+  }
+  /* An error occurred. */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+grpc_status_code gsec_aead_crypter_max_plaintext_length(
+    const gsec_aead_crypter* crypter, size_t ciphertext_and_tag_length,
+    size_t* max_plaintext_length_to_return, char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->max_plaintext_length != nullptr) {
+    return crypter->vtable->max_plaintext_length(
+        crypter, ciphertext_and_tag_length, max_plaintext_length_to_return,
+        error_details);
+  }
+  /* An error occurred. */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+grpc_status_code gsec_aead_crypter_nonce_length(
+    const gsec_aead_crypter* crypter, size_t* nonce_length_to_return,
+    char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->nonce_length != nullptr) {
+    return crypter->vtable->nonce_length(crypter, nonce_length_to_return,
+                                         error_details);
+  }
+  /* An error occurred. */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+grpc_status_code gsec_aead_crypter_key_length(const gsec_aead_crypter* crypter,
+                                              size_t* key_length_to_return,
+                                              char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->key_length != nullptr) {
+    return crypter->vtable->key_length(crypter, key_length_to_return,
+                                       error_details);
+  }
+  /* An error occurred */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+grpc_status_code gsec_aead_crypter_tag_length(const gsec_aead_crypter* crypter,
+                                              size_t* tag_length_to_return,
+                                              char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->tag_length != nullptr) {
+    return crypter->vtable->tag_length(crypter, tag_length_to_return,
+                                       error_details);
+  }
+  /* An error occurred. */
+  maybe_copy_error_msg(vtable_error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+void gsec_aead_crypter_destroy(gsec_aead_crypter* crypter) {
+  if (crypter != nullptr) {
+    if (crypter->vtable != nullptr && crypter->vtable->destruct != nullptr) {
+      crypter->vtable->destruct(crypter);
+    }
+    gpr_free(crypter);
+  }
+}
diff --git a/src/core/tsi/alts/crypt/gsec.h b/src/core/tsi/alts/crypt/gsec.h
new file mode 100644
index 0000000000..4d65caa944
--- /dev/null
+++ b/src/core/tsi/alts/crypt/gsec.h
@@ -0,0 +1,454 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_CRYPT_GSEC_H
+#define GRPC_CORE_TSI_ALTS_CRYPT_GSEC_H
+
+#include <grpc/support/port_platform.h>
+
+#include <assert.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include <grpc/grpc.h>
+
+struct iovec {
+  void* iov_base;
+  size_t iov_len;
+};
+
+/**
+ * A gsec interface for AEAD encryption schemes. The API is thread-compatible.
+ * Each implementation of this interface should specify supported values for
+ * key, nonce, and tag lengths.
+ */
+
+/* Key, nonce, and tag length in bytes */
+const size_t kAesGcmNonceLength = 12;
+const size_t kAesGcmTagLength = 16;
+const size_t kAes128GcmKeyLength = 16;
+const size_t kAes256GcmKeyLength = 32;
+
+// The first 32 bytes are used as a KDF key and the remaining 12 bytes are used
+// to mask the nonce.
+const size_t kAes128GcmRekeyKeyLength = 44;
+
+typedef struct gsec_aead_crypter gsec_aead_crypter;
+
+/**
+ * The gsec_aead_crypter is an API for different AEAD implementations such as
+ * AES_GCM. It encapsulates all AEAD-related operations in the format of
+ * V-table that stores pointers to functions implementing those operations.
+ * It also provides helper functions to wrap each of those function pointers.
+ *
+ * A typical usage of this object would be:
+ *
+ *------------------------------------------------------------------------------
+ * // Declare a gsec_aead_crypter object, and create and assign an instance
+ * // of specific AEAD implementation e.g., AES_GCM to it. We assume both
+ * // key and nonce contain cryptographically secure random bytes, and the key
+ * // can be derived from an upper-layer application.
+ * gsec_aead_crypter* crypter;
+ * char* error_in_creation;
+ * // User can populate the message with any 100 bytes data.
+ * uint8_t* message = gpr_malloc(100);
+ * grpc_status_code creation_status = gsec_aes_gcm_aead_crypter_create(key,
+ *                                                      kAes128GcmKeyLength,
+ *                                                      kAesGcmNonceLength,
+ *                                                      kAesGcmTagLength,
+ *                                                      &crypter,
+ *                                                      false,
+ *                                                      0
+ *                                                      &error_in_creation);
+ *
+ * if (creation_status == GRPC_STATUS_OK) {
+ *    // Allocate a correct amount of memory to hold a ciphertext.
+ *    size_t clength = 0;
+ *    gsec_aead_crypter_max_ciphertext_and_tag_length(crypter, 100, &clength,
+ *                                                    nullptr);
+ *    uint8_t* ciphertext = gpr_malloc(clength);
+ *
+ *    // Perform encryption
+ *    size_t num_encrypted_bytes = 0;
+ *    char* error_in_encryption = nullptr;
+ *    grpc_status_code status = gsec_aead_crypter_encrypt(crypter, nonce,
+ *                                                        kAesGcmNonceLength,
+ *                                                        nullptr, 0, message,
+ *                                                        100, ciphertext,
+ *                                                        clength,
+ *                                                        &num_encrypted_bytes,
+ *                                                        &error_in_encryption);
+ * if (status == GRPC_STATUS_OK) {
+ *       // Allocate a correct amount of memory to hold a plaintext.
+ *       size_t plength = 0;
+ *       gsec_aead_crypter_max_plaintext_length(crypter, num_encrypted_bytes,
+ *                                              &plength, nullptr);
+ *       uint8_t* plaintext = gpr_malloc(plength);
+ *
+ *       // Perform decryption.
+ *       size_t num_decrypted_bytes = 0;
+ *       char* error_in_decryption = nullptr;
+ *       status = gsec_aead_crypter_decrypt(crypter, nonce,
+ *                                          kAesGcmNonceLength, nullptr, 0,
+ *                                          ciphertext, num_encrypted_bytes,
+ *                                          plaintext, plength,
+ *                                          &num_decrypted_bytes,
+ *                                          &error_in_decryption);
+ *       if (status != GRPC_STATUS_OK) {
+ *         fprintf(stderr, "AEAD decrypt operation failed with error code:"
+ *                         "%d, message: %s\n", status, error_in_decryption);
+ *       }
+ *       ...
+ *       gpr_free(plaintext);
+ *       gpr_free(error_in_decryption);
+ *    } else {
+ *        fprintf(stderr, "AEAD encrypt operation failed with error code:"
+ *                        "%d, message: %s\n", status, error_in_encryption);
+ *    }
+ *    ...
+ *    gpr_free(ciphertext);
+ *    gpr_free(error_in_encryption);
+ * } else {
+ *   fprintf(stderr, "Creation of AEAD crypter instance failed with error code:"
+ *                   "%d, message: %s\n", creation_status, error_in_creation);
+ * }
+ *
+ * // Destruct AEAD crypter instance.
+ * if (creation_status == GRPC_STATUS_OK) {
+ *   gsec_aead_crypter_destroy(crypter);
+ * }
+ * gpr_free(error_in_creation);
+ * gpr_free(message);
+ * -----------------------------------------------------------------------------
+ */
+
+/* V-table for gsec AEAD operations */
+typedef struct gsec_aead_crypter_vtable {
+  grpc_status_code (*encrypt_iovec)(
+      gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+      const struct iovec* aad_vec, size_t aad_vec_length,
+      const struct iovec* plaintext_vec, size_t plaintext_vec_length,
+      struct iovec ciphertext_vec, size_t* ciphertext_bytes_written,
+      char** error_details);
+  grpc_status_code (*decrypt_iovec)(
+      gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+      const struct iovec* aad_vec, size_t aad_vec_length,
+      const struct iovec* ciphertext_vec, size_t ciphertext_vec_length,
+      struct iovec plaintext_vec, size_t* plaintext_bytes_written,
+      char** error_details);
+  grpc_status_code (*max_ciphertext_and_tag_length)(
+      const gsec_aead_crypter* crypter, size_t plaintext_length,
+      size_t* max_ciphertext_and_tag_length_to_return, char** error_details);
+  grpc_status_code (*max_plaintext_length)(
+      const gsec_aead_crypter* crypter, size_t ciphertext_and_tag_length,
+      size_t* max_plaintext_length_to_return, char** error_details);
+  grpc_status_code (*nonce_length)(const gsec_aead_crypter* crypter,
+                                   size_t* nonce_length_to_return,
+                                   char** error_details);
+  grpc_status_code (*key_length)(const gsec_aead_crypter* crypter,
+                                 size_t* key_length_to_return,
+                                 char** error_details);
+  grpc_status_code (*tag_length)(const gsec_aead_crypter* crypter,
+                                 size_t* tag_length_to_return,
+                                 char** error_details);
+  void (*destruct)(gsec_aead_crypter* crypter);
+} gsec_aead_crypter_vtable;
+
+/* Main struct for gsec interface */
+struct gsec_aead_crypter {
+  const struct gsec_aead_crypter_vtable* vtable;
+};
+
+/**
+ * This method performs an AEAD encrypt operation.
+ *
+ * - crypter: AEAD crypter instance.
+ * - nonce: buffer containing a nonce with its size equal to nonce_length.
+ * - nonce_length: size of nonce buffer, and must be equal to the value returned
+ *   from method gsec_aead_crypter_nonce_length.
+ * - aad: buffer containing data that needs to be authenticated but not
+ *   encrypted with its size equal to aad_length.
+ * - aad_length: size of aad buffer, which should be zero if the buffer is
+ *   nullptr.
+ * - plaintext: buffer containing data that needs to be both encrypted and
+ *   authenticated with its size equal to plaintext_length.
+ * - plaintext_length: size of plaintext buffer, which should be zero if
+ *   plaintext is nullptr.
+ * - ciphertext_and_tag: buffer that will contain ciphertext and tags the method
+ *   produced. The buffer should not overlap the plaintext buffer, and pointers
+ *   to those buffers should not be equal. Also if the ciphertext+tag buffer is
+ *   nullptr, the plaintext_length should be zero.
+ * - ciphertext_and_tag_length: size of ciphertext+tag buffer, which should be
+ *   at least as long as the one returned from method
+ *   gsec_aead_crypter_max_ciphertext_and_tag_length.
+ * - bytes_written: the actual number of bytes written to the ciphertext+tag
+ *   buffer. If bytes_written is nullptr, the plaintext_length should be zero.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of encryption, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ *
+ */
+grpc_status_code gsec_aead_crypter_encrypt(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const uint8_t* aad, size_t aad_length, const uint8_t* plaintext,
+    size_t plaintext_length, uint8_t* ciphertext_and_tag,
+    size_t ciphertext_and_tag_length, size_t* bytes_written,
+    char** error_details);
+
+/**
+ * This method performs an AEAD encrypt operation.
+ *
+ * - crypter: AEAD crypter instance.
+ * - nonce: buffer containing a nonce with its size equal to nonce_length.
+ * - nonce_length: size of nonce buffer, and must be equal to the value returned
+ *   from method gsec_aead_crypter_nonce_length.
+ * - aad_vec: an iovec array containing data that needs to be authenticated but
+ *   not encrypted.
+ * - aad_vec_length: the array length of aad_vec.
+ * - plaintext_vec: an iovec array containing data that needs to be both
+ *   encrypted and authenticated.
+ * - plaintext_vec_length: the array length of plaintext_vec.
+ * - ciphertext_vec: an iovec containing a ciphertext buffer. The buffer should
+ *   not overlap the plaintext buffer.
+ * - ciphertext_bytes_written: the actual number of bytes written to
+ *   ciphertext_vec.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of encryption, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ *
+ */
+grpc_status_code gsec_aead_crypter_encrypt_iovec(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const struct iovec* aad_vec, size_t aad_vec_length,
+    const struct iovec* plaintext_vec, size_t plaintext_vec_length,
+    struct iovec ciphertext_vec, size_t* ciphertext_bytes_written,
+    char** error_details);
+
+/**
+ * This method performs an AEAD decrypt operation.
+ *
+ * - crypter: AEAD crypter instance.
+ * - nonce: buffer containing a nonce with its size equal to nonce_length.
+ * - nonce_length: size of nonce buffer, and must be equal to the value returned
+ *   from method gsec_aead_crypter_nonce_length.
+ * - aad: buffer containing data that needs to be authenticated only.
+ * - aad_length: size of aad buffer, which should be zero if the buffer is
+ *   nullptr.
+ * - ciphertext_and_tag: buffer containing ciphertext and tag.
+ * - ciphertext_and_tag_length: length of ciphertext and tag. It should be zero
+ *   if any of plaintext, ciphertext_and_tag, or bytes_written is nullptr. Also,
+ *   ciphertext_and_tag_length should be at least as large as the tag length set
+ *   at AEAD crypter instance construction time.
+ * - plaintext: buffer containing decrypted and authenticated data the method
+ *   produced. The buffer should not overlap with the ciphertext+tag buffer, and
+ *   pointers to those buffers should not be equal.
+ * - plaintext_length: size of plaintext buffer, which should be at least as
+ *   long as the one returned from gsec_aead_crypter_max_plaintext_length
+ *   method.
+ * - bytes_written: the actual number of bytes written to the plaintext
+ *   buffer.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of decryption, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code gsec_aead_crypter_decrypt(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const uint8_t* aad, size_t aad_length, const uint8_t* ciphertext_and_tag,
+    size_t ciphertext_and_tag_length, uint8_t* plaintext,
+    size_t plaintext_length, size_t* bytes_written, char** error_details);
+
+/**
+ * This method performs an AEAD decrypt operation.
+ *
+ * - crypter: AEAD crypter instance.
+ * - nonce: buffer containing a nonce with its size equal to nonce_length.
+ * - nonce_length: size of nonce buffer, and must be equal to the value returned
+ *   from method gsec_aead_crypter_nonce_length.
+ * - aad_vec: an iovec array containing data that needs to be authenticated but
+ *   not encrypted.
+ * - aad_vec_length: the array length of aad_vec.
+ * - ciphertext_vec: an iovec array containing the ciphertext and tag.
+ * - ciphertext_vec_length: the array length of ciphertext_vec.
+ * - plaintext_vec: an iovec containing a plaintext buffer. The buffer should
+ *   not overlap the ciphertext buffer.
+ * - plaintext_bytes_written: the actual number of bytes written to
+ *   plaintext_vec.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of decryption, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code gsec_aead_crypter_decrypt_iovec(
+    gsec_aead_crypter* crypter, const uint8_t* nonce, size_t nonce_length,
+    const struct iovec* aad_vec, size_t aad_vec_length,
+    const struct iovec* ciphertext_vec, size_t ciphertext_vec_length,
+    struct iovec plaintext_vec, size_t* plaintext_bytes_written,
+    char** error_details);
+
+/**
+ * This method computes the size of ciphertext+tag buffer that must be passed to
+ * gsec_aead_crypter_encrypt function to ensure correct encryption of a
+ * plaintext. The actual size of ciphertext+tag written to the buffer could be
+ * smaller.
+ *
+ * - crypter: AEAD crypter instance.
+ * - plaintext_length: length of plaintext.
+ * - max_ciphertext_and_tag_length_to_return: the size of ciphertext+tag buffer
+ *   the method returns.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of execution, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code gsec_aead_crypter_max_ciphertext_and_tag_length(
+    const gsec_aead_crypter* crypter, size_t plaintext_length,
+    size_t* max_ciphertext_and_tag_length_to_return, char** error_details);
+
+/**
+ * This method computes the size of plaintext buffer that must be passed to
+ * gsec_aead_crypter_decrypt function to ensure correct decryption of a
+ * ciphertext. The actual size of plaintext written to the buffer could be
+ * smaller.
+ *
+ * - crypter: AEAD crypter instance.
+ * - ciphertext_and_tag_length: length of ciphertext and tag.
+ * - max_plaintext_length_to_return: the size of plaintext buffer the method
+ *   returns.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of execution, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code gsec_aead_crypter_max_plaintext_length(
+    const gsec_aead_crypter* crypter, size_t ciphertext_and_tag_length,
+    size_t* max_plaintext_length_to_return, char** error_details);
+
+/**
+ * This method returns a valid size of nonce array used at the construction of
+ * AEAD crypter instance. It is also the size that should be passed to encrypt
+ * and decrypt methods executed on the instance.
+ *
+ * - crypter: AEAD crypter instance.
+ * - nonce_length_to_return: the length of nonce array the method returns.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of execution, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code gsec_aead_crypter_nonce_length(
+    const gsec_aead_crypter* crypter, size_t* nonce_length_to_return,
+    char** error_details);
+
+/**
+ * This method returns a valid size of key array used at the construction of
+ * AEAD crypter instance. It is also the size that should be passed to encrypt
+ * and decrypt methods executed on the instance.
+ *
+ * - crypter: AEAD crypter instance.
+ * - key_length_to_return: the length of key array the method returns.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of execution, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code gsec_aead_crypter_key_length(const gsec_aead_crypter* crypter,
+                                              size_t* key_length_to_return,
+                                              char** error_details);
+/**
+ * This method returns a valid size of tag array used at the construction of
+ * AEAD crypter instance. It is also the size that should be passed to encrypt
+ * and decrypt methods executed on the instance.
+ *
+ * - crypter: AEAD crypter instance.
+ * - tag_length_to_return: the length of tag array the method returns.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On the success of execution, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code gsec_aead_crypter_tag_length(const gsec_aead_crypter* crypter,
+                                              size_t* tag_length_to_return,
+                                              char** error_details);
+
+/**
+ * This method destroys an AEAD crypter instance by de-allocating all of its
+ * occupied memory.
+ *
+ * - crypter: AEAD crypter instance that needs to be destroyed.
+ */
+void gsec_aead_crypter_destroy(gsec_aead_crypter* crypter);
+
+/**
+ * This method creates an AEAD crypter instance of AES-GCM encryption scheme
+ * which supports 16 and 32 bytes long keys, 12 and 16 bytes long nonces, and
+ * 16 bytes long tags. It should be noted that once the lengths of key, nonce,
+ * and tag are determined at construction time, they cannot be modified later.
+ *
+ * - key: buffer containing a key which is binded with AEAD crypter instance.
+ * - key_length: length of a key in bytes, which should be 44 if rekeying is
+ *   enabled and 16 or 32 otherwise.
+ * - nonce_length: length of a nonce in bytes, which should be either 12 or 16.
+ * - tag_length: length of a tag in bytes, which should be always 16.
+ * - rekey: enable nonce-based rekeying and nonce-masking.
+ * - crypter: address of AES_GCM crypter instance returned from the method.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On success of instance creation, it stores the address of instance at
+ * crypter. Otherwise, it returns an error status code together with its details
+ * specified in error_details.
+ */
+grpc_status_code gsec_aes_gcm_aead_crypter_create(const uint8_t* key,
+                                                  size_t key_length,
+                                                  size_t nonce_length,
+                                                  size_t tag_length, bool rekey,
+                                                  gsec_aead_crypter** crypter,
+                                                  char** error_details);
+
+#endif /* GRPC_CORE_TSI_ALTS_CRYPT_GSEC_H */
diff --git a/src/core/tsi/alts/frame_protector/alts_counter.cc b/src/core/tsi/alts/frame_protector/alts_counter.cc
new file mode 100644
index 0000000000..de163e3e08
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_counter.cc
@@ -0,0 +1,118 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/frame_protector/alts_counter.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+
+static void maybe_copy_error_msg(const char* src, char** dst) {
+  if (dst != nullptr && src != nullptr) {
+    *dst = static_cast<char*>(gpr_malloc(strlen(src) + 1));
+    memcpy(*dst, src, strlen(src) + 1);
+  }
+}
+
+grpc_status_code alts_counter_create(bool is_client, size_t counter_size,
+                                     size_t overflow_size,
+                                     alts_counter** crypter_counter,
+                                     char** error_details) {
+  /* Perform input sanity check. */
+  if (counter_size == 0) {
+    const char error_msg[] = "counter_size is invalid.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (overflow_size == 0 || overflow_size >= counter_size) {
+    const char error_msg[] = "overflow_size is invalid.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (crypter_counter == nullptr) {
+    const char error_msg[] = "crypter_counter is nullptr.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  *crypter_counter =
+      static_cast<alts_counter*>(gpr_malloc(sizeof(**crypter_counter)));
+  (*crypter_counter)->size = counter_size;
+  (*crypter_counter)->overflow_size = overflow_size;
+  (*crypter_counter)->counter =
+      static_cast<unsigned char*>(gpr_zalloc(counter_size));
+  if (is_client) {
+    ((*crypter_counter)->counter)[counter_size - 1] = 0x80;
+  }
+  return GRPC_STATUS_OK;
+}
+
+grpc_status_code alts_counter_increment(alts_counter* crypter_counter,
+                                        bool* is_overflow,
+                                        char** error_details) {
+  /* Perform input sanity check. */
+  if (crypter_counter == nullptr) {
+    const char error_msg[] = "crypter_counter is nullptr.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (is_overflow == nullptr) {
+    const char error_msg[] = "is_overflow is nullptr.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  /* Increment the internal counter. */
+  size_t i = 0;
+  for (; i < crypter_counter->overflow_size; i++) {
+    (crypter_counter->counter)[i]++;
+    if ((crypter_counter->counter)[i] != 0x00) {
+      break;
+    }
+  }
+  /**
+   * If the lower overflow_size bytes are all zero, the counter has overflowed.
+   */
+  if (i == crypter_counter->overflow_size) {
+    *is_overflow = true;
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  *is_overflow = false;
+  return GRPC_STATUS_OK;
+}
+
+size_t alts_counter_get_size(alts_counter* crypter_counter) {
+  if (crypter_counter == nullptr) {
+    return 0;
+  }
+  return crypter_counter->size;
+}
+
+unsigned char* alts_counter_get_counter(alts_counter* crypter_counter) {
+  if (crypter_counter == nullptr) {
+    return nullptr;
+  }
+  return crypter_counter->counter;
+}
+
+void alts_counter_destroy(alts_counter* crypter_counter) {
+  if (crypter_counter != nullptr) {
+    gpr_free(crypter_counter->counter);
+    gpr_free(crypter_counter);
+  }
+}
diff --git a/src/core/tsi/alts/frame_protector/alts_counter.h b/src/core/tsi/alts/frame_protector/alts_counter.h
new file mode 100644
index 0000000000..d705638fa8
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_counter.h
@@ -0,0 +1,98 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_COUNTER_H
+#define GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_COUNTER_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stdbool.h>
+#include <stdlib.h>
+
+#include <grpc/grpc.h>
+
+/* Main struct for a crypter counter managed within seal/unseal operations. */
+typedef struct alts_counter {
+  size_t size;
+  size_t overflow_size;
+  unsigned char* counter;
+} alts_counter;
+
+/**
+ * This method creates and initializes an alts_counter instance.
+ *
+ * - is_client: a flag indicating if the alts_counter instance will be used
+ *   at client (is_client = true) or server (is_client = false) side.
+ * - counter_size: size of buffer holding the counter value.
+ * - overflow_size: overflow size in bytes. The counter instance can be used
+ *   to produce at most 2^(overflow_size*8) frames.
+ * - crypter_counter: an alts_counter instance to be returned from the method.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code alts_counter_create(bool is_client, size_t counter_size,
+                                     size_t overflow_size,
+                                     alts_counter** crypter_counter,
+                                     char** error_details);
+
+/**
+ * This method increments the internal counter.
+ *
+ * - crypter_counter: an alts_counter instance.
+ * - is_overflow: after incrementing the internal counter, if an overflow
+ *   occurs, is_overflow is set to true, and no further calls to
+ *   alts_counter_increment() should be made. Otherwise, is_overflow is set to
+ *   false.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code alts_counter_increment(alts_counter* crypter_counter,
+                                        bool* is_overflow,
+                                        char** error_details);
+
+/**
+ * This method returns the size of counter buffer.
+ *
+ * - crypter_counter: an alts_counter instance.
+ */
+size_t alts_counter_get_size(alts_counter* crypter_counter);
+
+/**
+ * This method returns the counter buffer.
+ *
+ * - crypter_counter: an alts_counter instance.
+ */
+unsigned char* alts_counter_get_counter(alts_counter* crypter_counter);
+
+/**
+ * This method de-allocates all memory allocated to an alts_coutner instance.
+ * - crypter_counter: an alts_counter instance.
+ */
+void alts_counter_destroy(alts_counter* crypter_counter);
+
+#endif /* GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_COUNTER_H */
diff --git a/src/core/tsi/alts/frame_protector/alts_crypter.cc b/src/core/tsi/alts/frame_protector/alts_crypter.cc
new file mode 100644
index 0000000000..56f0512186
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_crypter.cc
@@ -0,0 +1,66 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/frame_protector/alts_crypter.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+
+static void maybe_copy_error_msg(const char* src, char** dst) {
+  if (dst != nullptr && src != nullptr) {
+    *dst = static_cast<char*>(gpr_malloc(strlen(src) + 1));
+    memcpy(*dst, src, strlen(src) + 1);
+  }
+}
+
+grpc_status_code alts_crypter_process_in_place(
+    alts_crypter* crypter, unsigned char* data, size_t data_allocated_size,
+    size_t data_size, size_t* output_size, char** error_details) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->process_in_place != nullptr) {
+    return crypter->vtable->process_in_place(crypter, data, data_allocated_size,
+                                             data_size, output_size,
+                                             error_details);
+  }
+  /* An error occurred. */
+  const char error_msg[] =
+      "crypter or crypter->vtable has not been initialized properly.";
+  maybe_copy_error_msg(error_msg, error_details);
+  return GRPC_STATUS_INVALID_ARGUMENT;
+}
+
+size_t alts_crypter_num_overhead_bytes(const alts_crypter* crypter) {
+  if (crypter != nullptr && crypter->vtable != nullptr &&
+      crypter->vtable->num_overhead_bytes != nullptr) {
+    return crypter->vtable->num_overhead_bytes(crypter);
+  }
+  /* An error occurred. */
+  return 0;
+}
+
+void alts_crypter_destroy(alts_crypter* crypter) {
+  if (crypter != nullptr) {
+    if (crypter->vtable != nullptr && crypter->vtable->destruct != nullptr) {
+      crypter->vtable->destruct(crypter);
+    }
+    gpr_free(crypter);
+  }
+}
diff --git a/src/core/tsi/alts/frame_protector/alts_crypter.h b/src/core/tsi/alts/frame_protector/alts_crypter.h
new file mode 100644
index 0000000000..3140778f4f
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_crypter.h
@@ -0,0 +1,255 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_CRYPTER_H
+#define GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_CRYPTER_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stdbool.h>
+#include <string.h>
+
+#include <grpc/grpc.h>
+
+#include "src/core/tsi/alts/crypt/gsec.h"
+
+/**
+ * An alts_crypter interface for an ALTS record protocol providing
+ * seal/unseal functionality. The interface is thread-compatible.
+ */
+
+typedef struct alts_crypter alts_crypter;
+
+/**
+ * A typical usage of the interface would be
+ *------------------------------------------------------------------------------
+ * // Perform a seal operation. We assume the gsec_aead_crypter instance -
+ * // client_aead_crypter is created beforehand with a 16-byte key and 12-byte
+ * // nonce length.
+ *
+ * alts_crypter* client = nullptr;
+ * char* client_error_in_creation = nullptr;
+ * unsigned char* data = nullptr;
+ * grpc_status_code client_status =
+ *                 alts_seal_crypter_create(client_aead_crypter, 1, 5, &client,
+ *                                          &client_error_in_creation);
+ * if (client_status == GRPC_STATUS_OK) {
+ *   size_t data_size = 100;
+ *   size_t num_overhead_bytes = alts_crypter_num_overhead_bytes(client);
+ *   size_t data_allocated_size = data_size + num_overhead_bytes;
+ *   data = gpr_malloc(data_allocated_size);
+ *   char* client_error_in_seal = nullptr;
+ *   // Client performs a seal operation.
+ *   client_status = alts_crypter_process_in_place(client, data,
+ *                                                 data_allocated_size,
+ *                                                 &data_size,
+ *                                                 &client_error_in_seal);
+ *   if (client_status != GRPC_STATUS_OK) {
+ *     fprintf(stderr, "seal operation failed with error code:"
+ *                     "%d, message: %s\n", client_status,
+ *                      client_error_in_seal);
+ *    }
+ *    gpr_free(client_error_in_seal);
+ * } else {
+ *     fprintf(stderr, "alts_crypter instance creation failed with error"
+ *                     "code: %d, message: %s\n", client_status,
+ *                      client_error_in_creation);
+ * }
+ *
+ * ...
+ *
+ * gpr_free(client_error_in_creation);
+ * alts_crypter_destroy(client);
+ *
+ * ...
+ *
+ * // Perform an unseal operation. We assume the gsec_aead_crypter instance -
+ * // server_aead_crypter is created beforehand with a 16-byte key and 12-byte
+ * // nonce length. The key used in the creation of gsec_aead_crypter instances
+ * // at server and client sides should be identical.
+ *
+ * alts_crypter* server = nullptr;
+ * char* server_error_in_creation = nullptr;
+ * grpc_status_code server_status =
+ *               alts_unseal_crypter_create(server_aead_crypter, 0, 5, &server,
+ *                                          &server_error_in_creation);
+ * if (server_status == GRPC_STATUS_OK) {
+ *   size_t num_overhead_bytes = alts_crypter_num_overhead_bytes(server);
+ *   size_t data_size = 100 + num_overhead_bytes;
+ *   size_t data_allocated_size = data_size;
+ *   char* server_error_in_unseal = nullptr;
+ *   // Server performs an unseal operation.
+ *   server_status = alts_crypter_process_in_place(server, data,
+ *                                                 data_allocated_size,
+ *                                                 &data_size,
+ *                                                 &server_error_in_unseal);
+ *   if (server_status != GRPC_STATUS_OK) {
+ *     fprintf(stderr, "unseal operation failed with error code:"
+ *                     "%d, message: %s\n", server_status,
+ *                      server_error_in_unseal);
+ *   }
+ *   gpr_free(server_error_in_unseal);
+ * } else {
+ *     fprintf(stderr, "alts_crypter instance creation failed with error"
+ *                     "code: %d, message: %s\n", server_status,
+ *                      server_error_in_creation);
+ * }
+ *
+ * ...
+ *
+ * gpr_free(data);
+ * gpr_free(server_error_in_creation);
+ * alts_crypter_destroy(server);
+ *
+ * ...
+ *------------------------------------------------------------------------------
+ */
+
+/* V-table for alts_crypter operations */
+typedef struct alts_crypter_vtable {
+  size_t (*num_overhead_bytes)(const alts_crypter* crypter);
+  grpc_status_code (*process_in_place)(alts_crypter* crypter,
+                                       unsigned char* data,
+                                       size_t data_allocated_size,
+                                       size_t data_size, size_t* output_size,
+                                       char** error_details);
+  void (*destruct)(alts_crypter* crypter);
+} alts_crypter_vtable;
+
+/* Main struct for alts_crypter interface */
+struct alts_crypter {
+  const alts_crypter_vtable* vtable;
+};
+
+/**
+ * This method gets the number of overhead bytes needed for sealing data that
+ * is the difference in size between the protected and raw data. The counter
+ * value used in a seal or unseal operation is locally maintained (not sent or
+ * received from the other peer) and therefore, will not be counted as part of
+ * overhead bytes.
+ *
+ * - crypter: an alts_crypter instance.
+ *
+ * On success, the method returns the number of overhead bytes. Otherwise, it
+ * returns zero.
+ *
+ */
+size_t alts_crypter_num_overhead_bytes(const alts_crypter* crypter);
+
+/**
+ * This method performs either a seal or an unseal operation depending on the
+ * alts_crypter instance - crypter passed to the method. If the crypter is
+ * an instance implementing a seal operation, the method will perform a seal
+ * operation. That is, it seals raw data and stores the result in-place, and the
+ * memory allocated for data must be at least data_length +
+ * alts_crypter_num_overhead_bytes(). If the crypter is an instance
+ * implementing an unseal operation, the method will perform an unseal
+ * operation. That is, it unseals protected data and stores the result in-place.
+ * The size of unsealed data will be data_length -
+ * alts_crypter_num_overhead_bytes(). Integrity tag will be verified during
+ * the unseal operation, and if verification fails, the data will be wiped.
+ * The counters used in both seal and unseal operations are managed internally.
+ *
+ * - crypter: an alts_crypter instance.
+ * - data: if the method performs a seal operation, the data represents raw data
+ *   that needs to be sealed. It also plays the role of buffer to hold the
+ *   protected data as a result of seal. If the method performs an unseal
+ *   operation, the data represents protected data that needs to be unsealed. It
+ *   also plays the role of buffer to hold raw data as a result of unseal.
+ * - data_allocated_size: the size of data buffer. The parameter is used to
+ *   check whether the result of either seal or unseal can be safely written to
+ *   the data buffer.
+ * - data_size: if the method performs a seal operation, data_size
+ *   represents the size of raw data that needs to be sealed, and if the method
+ *   performs an unseal operation, data_size represents the size of protected
+ *   data that needs to be unsealed.
+ * - output_size: size of data written to the data buffer after a seal or an
+ *   unseal operation.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is legal to pass nullptr into error_details and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code alts_crypter_process_in_place(
+    alts_crypter* crypter, unsigned char* data, size_t data_allocated_size,
+    size_t data_size, size_t* output_size, char** error_details);
+
+/**
+ * This method creates an alts_crypter instance to be used to perform a seal
+ * operation, given a gsec_aead_crypter instance and a flag indicating if the
+ * created instance will be used at the client or server side. It takes
+ * ownership of gsec_aead_crypter instance.
+ *
+ * - gc: a gsec_aead_crypter instance used to perform AEAD encryption.
+ * - is_client: a flag indicating if the alts_crypter instance will be
+ *   used at the client (is_client = true) or server (is_client =
+ *   false) side.
+ * - overflow_size: overflow size of counter in bytes.
+ * - crypter: an alts_crypter instance to be returned from the method.
+ * - error_details: a buffer containing an error message if the method does
+ *   not function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On success of creation, the method returns GRPC_STATUS_OK.
+ * Otherwise, it returns an error status code along with its details specified
+ * in error_details (if error_details is not nullptr).
+ */
+grpc_status_code alts_seal_crypter_create(gsec_aead_crypter* gc, bool is_client,
+                                          size_t overflow_size,
+                                          alts_crypter** crypter,
+                                          char** error_details);
+
+/**
+ * This method creates an alts_crypter instance used to perform an unseal
+ * operation, given a gsec_aead_crypter instance and a flag indicating if the
+ * created instance will be used at the client or server side. It takes
+ * ownership of gsec_aead_crypter instance.
+ *
+ * - gc: a gsec_aead_crypter instance used to perform AEAD decryption.
+ * - is_client: a flag indicating if the alts_crypter instance will be
+ *   used at the client (is_client = true) or server (is_client =
+ *   false) side.
+ * - overflow_size: overflow size of counter in bytes.
+ * - crypter: an alts_crypter instance to be returned from the method.
+ * - error_details: a buffer containing an error message if the method does
+ *   not function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On success of creation, the method returns GRPC_STATUS_OK.
+ * Otherwise, it returns an error status code along with its details specified
+ * in error_details (if error_details is not nullptr).
+ */
+grpc_status_code alts_unseal_crypter_create(gsec_aead_crypter* gc,
+                                            bool is_client,
+                                            size_t overflow_size,
+                                            alts_crypter** crypter,
+                                            char** error_details);
+
+/**
+ * This method destroys an alts_crypter instance by de-allocating all of its
+ * occupied memory. A gsec_aead_crypter instance passed in at alts_crypter
+ * instance creation time will be destroyed in this method.
+ *
+ * - crypter: an alts_crypter instance.
+ */
+void alts_crypter_destroy(alts_crypter* crypter);
+
+#endif /* GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_CRYPTER_H */
diff --git a/src/core/tsi/alts/frame_protector/alts_frame_protector.cc b/src/core/tsi/alts/frame_protector/alts_frame_protector.cc
new file mode 100644
index 0000000000..bfa0b7a720
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_frame_protector.cc
@@ -0,0 +1,407 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/frame_protector/alts_frame_protector.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/lib/gpr/useful.h"
+#include "src/core/tsi/alts/crypt/gsec.h"
+#include "src/core/tsi/alts/frame_protector/alts_crypter.h"
+#include "src/core/tsi/alts/frame_protector/frame_handler.h"
+#include "src/core/tsi/transport_security.h"
+
+constexpr size_t kMinFrameLength = 1024;
+constexpr size_t kDefaultFrameLength = 16 * 1024;
+constexpr size_t kMaxFrameLength = 1024 * 1024;
+
+// Limit k on number of frames such that at most 2^(8 * k) frames can be sent.
+constexpr size_t kAltsRecordProtocolRekeyFrameLimit = 8;
+constexpr size_t kAltsRecordProtocolFrameLimit = 5;
+
+/* Main struct for alts_frame_protector. */
+struct alts_frame_protector {
+  tsi_frame_protector base;
+  alts_crypter* seal_crypter;
+  alts_crypter* unseal_crypter;
+  alts_frame_writer* writer;
+  alts_frame_reader* reader;
+  unsigned char* in_place_protect_buffer;
+  unsigned char* in_place_unprotect_buffer;
+  size_t in_place_protect_bytes_buffered;
+  size_t in_place_unprotect_bytes_processed;
+  size_t max_protected_frame_size;
+  size_t max_unprotected_frame_size;
+  size_t overhead_length;
+  size_t counter_overflow;
+};
+
+static tsi_result seal(alts_frame_protector* impl) {
+  char* error_details = nullptr;
+  size_t output_size = 0;
+  grpc_status_code status = alts_crypter_process_in_place(
+      impl->seal_crypter, impl->in_place_protect_buffer,
+      impl->max_protected_frame_size, impl->in_place_protect_bytes_buffered,
+      &output_size, &error_details);
+  impl->in_place_protect_bytes_buffered = output_size;
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "%s", error_details);
+    gpr_free(error_details);
+    return TSI_INTERNAL_ERROR;
+  }
+  return TSI_OK;
+}
+
+static size_t max_encrypted_payload_bytes(alts_frame_protector* impl) {
+  return impl->max_protected_frame_size - kFrameHeaderSize;
+}
+
+static tsi_result alts_protect_flush(tsi_frame_protector* self,
+                                     unsigned char* protected_output_frames,
+                                     size_t* protected_output_frames_size,
+                                     size_t* still_pending_size) {
+  if (self == nullptr || protected_output_frames == nullptr ||
+      protected_output_frames_size == nullptr ||
+      still_pending_size == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid nullptr arguments to alts_protect_flush().");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_frame_protector* impl = reinterpret_cast<alts_frame_protector*>(self);
+  /**
+   * If there's nothing to flush (i.e., in_place_protect_buffer is empty),
+   * we're done.
+   */
+  if (impl->in_place_protect_bytes_buffered == 0) {
+    *protected_output_frames_size = 0;
+    *still_pending_size = 0;
+    return TSI_OK;
+  }
+  /**
+   * If a new frame can start being processed, we encrypt the payload and reset
+   * the frame writer to point to in_place_protect_buffer that holds the newly
+   * sealed frame.
+   */
+  if (alts_is_frame_writer_done(impl->writer)) {
+    tsi_result result = seal(impl);
+    if (result != TSI_OK) {
+      return result;
+    }
+    if (!alts_reset_frame_writer(impl->writer, impl->in_place_protect_buffer,
+                                 impl->in_place_protect_bytes_buffered)) {
+      gpr_log(GPR_ERROR, "Couldn't reset frame writer.");
+      return TSI_INTERNAL_ERROR;
+    }
+  }
+  /**
+   * Write the sealed frame as much as possible to protected_output_frames. It's
+   * possible a frame will not be written out completely by a single flush
+   * (i.e., still_pending_size != 0), in which case the flush should be called
+   * iteratively until a complete frame has been written out.
+   */
+  size_t written_frame_bytes = *protected_output_frames_size;
+  if (!alts_write_frame_bytes(impl->writer, protected_output_frames,
+                              &written_frame_bytes)) {
+    gpr_log(GPR_ERROR, "Couldn't write frame bytes.");
+    return TSI_INTERNAL_ERROR;
+  }
+  *protected_output_frames_size = written_frame_bytes;
+  *still_pending_size = alts_get_num_writer_bytes_remaining(impl->writer);
+  /**
+   * If the current frame has been finished processing (i.e., sealed and written
+   * out completely), we empty in_place_protect_buffer.
+   */
+  if (alts_is_frame_writer_done(impl->writer)) {
+    impl->in_place_protect_bytes_buffered = 0;
+  }
+  return TSI_OK;
+}
+
+static tsi_result alts_protect(tsi_frame_protector* self,
+                               const unsigned char* unprotected_bytes,
+                               size_t* unprotected_bytes_size,
+                               unsigned char* protected_output_frames,
+                               size_t* protected_output_frames_size) {
+  if (self == nullptr || unprotected_bytes == nullptr ||
+      unprotected_bytes_size == nullptr || protected_output_frames == nullptr ||
+      protected_output_frames_size == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid nullptr arguments to alts_protect().");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_frame_protector* impl = reinterpret_cast<alts_frame_protector*>(self);
+
+  /**
+   * If more payload can be buffered, we buffer it as much as possible to
+   * in_place_protect_buffer.
+   */
+  if (impl->in_place_protect_bytes_buffered + impl->overhead_length <
+      max_encrypted_payload_bytes(impl)) {
+    size_t bytes_to_buffer = GPR_MIN(*unprotected_bytes_size,
+                                     max_encrypted_payload_bytes(impl) -
+                                         impl->in_place_protect_bytes_buffered -
+                                         impl->overhead_length);
+    *unprotected_bytes_size = bytes_to_buffer;
+    if (bytes_to_buffer > 0) {
+      memcpy(
+          impl->in_place_protect_buffer + impl->in_place_protect_bytes_buffered,
+          unprotected_bytes, bytes_to_buffer);
+      impl->in_place_protect_bytes_buffered += bytes_to_buffer;
+    }
+  } else {
+    *unprotected_bytes_size = 0;
+  }
+  /**
+   * If a full frame has been buffered, we output it. If the first condition
+   * holds, then there exists an unencrypted full frame. If the second
+   * condition holds, then there exists a full frame that has already been
+   * encrypted.
+   */
+  if (max_encrypted_payload_bytes(impl) ==
+          impl->in_place_protect_bytes_buffered + impl->overhead_length ||
+      max_encrypted_payload_bytes(impl) ==
+          impl->in_place_protect_bytes_buffered) {
+    size_t still_pending_size = 0;
+    return alts_protect_flush(self, protected_output_frames,
+                              protected_output_frames_size,
+                              &still_pending_size);
+  } else {
+    *protected_output_frames_size = 0;
+    return TSI_OK;
+  }
+}
+
+static tsi_result unseal(alts_frame_protector* impl) {
+  char* error_details = nullptr;
+  size_t output_size = 0;
+  grpc_status_code status = alts_crypter_process_in_place(
+      impl->unseal_crypter, impl->in_place_unprotect_buffer,
+      impl->max_unprotected_frame_size,
+      alts_get_output_bytes_read(impl->reader), &output_size, &error_details);
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "%s", error_details);
+    gpr_free(error_details);
+    return TSI_DATA_CORRUPTED;
+  }
+  return TSI_OK;
+}
+
+static void ensure_buffer_size(alts_frame_protector* impl) {
+  if (!alts_has_read_frame_length(impl->reader)) {
+    return;
+  }
+  size_t buffer_space_remaining = impl->max_unprotected_frame_size -
+                                  alts_get_output_bytes_read(impl->reader);
+  /**
+   * Check if we need to resize in_place_unprotect_buffer in order to hold
+   * remaining bytes of a full frame.
+   */
+  if (buffer_space_remaining < alts_get_reader_bytes_remaining(impl->reader)) {
+    size_t buffer_len = alts_get_output_bytes_read(impl->reader) +
+                        alts_get_reader_bytes_remaining(impl->reader);
+    unsigned char* buffer = static_cast<unsigned char*>(gpr_malloc(buffer_len));
+    memcpy(buffer, impl->in_place_unprotect_buffer,
+           alts_get_output_bytes_read(impl->reader));
+    impl->max_unprotected_frame_size = buffer_len;
+    gpr_free(impl->in_place_unprotect_buffer);
+    impl->in_place_unprotect_buffer = buffer;
+    alts_reset_reader_output_buffer(
+        impl->reader, buffer + alts_get_output_bytes_read(impl->reader));
+  }
+}
+
+static tsi_result alts_unprotect(tsi_frame_protector* self,
+                                 const unsigned char* protected_frames_bytes,
+                                 size_t* protected_frames_bytes_size,
+                                 unsigned char* unprotected_bytes,
+                                 size_t* unprotected_bytes_size) {
+  if (self == nullptr || protected_frames_bytes == nullptr ||
+      protected_frames_bytes_size == nullptr || unprotected_bytes == nullptr ||
+      unprotected_bytes_size == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid nullptr arguments to alts_unprotect().");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_frame_protector* impl = reinterpret_cast<alts_frame_protector*>(self);
+  /**
+   * If a new frame can start being processed, we reset the frame reader to
+   * point to in_place_unprotect_buffer that will be used to hold deframed
+   * result.
+   */
+  if (alts_is_frame_reader_done(impl->reader) &&
+      ((alts_get_output_buffer(impl->reader) == nullptr) ||
+       (alts_get_output_bytes_read(impl->reader) ==
+        impl->in_place_unprotect_bytes_processed + impl->overhead_length))) {
+    if (!alts_reset_frame_reader(impl->reader,
+                                 impl->in_place_unprotect_buffer)) {
+      gpr_log(GPR_ERROR, "Couldn't reset frame reader.");
+      return TSI_INTERNAL_ERROR;
+    }
+    impl->in_place_unprotect_bytes_processed = 0;
+  }
+  /**
+   * If a full frame has not yet been read, we read more bytes from
+   * protected_frames_bytes until a full frame has been read. We also need to
+   * make sure in_place_unprotect_buffer is large enough to hold a complete
+   * frame.
+   */
+  if (!alts_is_frame_reader_done(impl->reader)) {
+    ensure_buffer_size(impl);
+    *protected_frames_bytes_size =
+        GPR_MIN(impl->max_unprotected_frame_size -
+                    alts_get_output_bytes_read(impl->reader),
+                *protected_frames_bytes_size);
+    size_t read_frames_bytes_size = *protected_frames_bytes_size;
+    if (!alts_read_frame_bytes(impl->reader, protected_frames_bytes,
+                               &read_frames_bytes_size)) {
+      gpr_log(GPR_ERROR, "Failed to process frame.");
+      return TSI_INTERNAL_ERROR;
+    }
+    *protected_frames_bytes_size = read_frames_bytes_size;
+  } else {
+    *protected_frames_bytes_size = 0;
+  }
+  /**
+   * If a full frame has been read, we unseal it, and write out the
+   * deframed result to unprotected_bytes.
+   */
+  if (alts_is_frame_reader_done(impl->reader)) {
+    if (impl->in_place_unprotect_bytes_processed == 0) {
+      tsi_result result = unseal(impl);
+      if (result != TSI_OK) {
+        return result;
+      }
+    }
+    size_t bytes_to_write = GPR_MIN(
+        *unprotected_bytes_size, alts_get_output_bytes_read(impl->reader) -
+                                     impl->in_place_unprotect_bytes_processed -
+                                     impl->overhead_length);
+    if (bytes_to_write > 0) {
+      memcpy(unprotected_bytes,
+             impl->in_place_unprotect_buffer +
+                 impl->in_place_unprotect_bytes_processed,
+             bytes_to_write);
+    }
+    *unprotected_bytes_size = bytes_to_write;
+    impl->in_place_unprotect_bytes_processed += bytes_to_write;
+    return TSI_OK;
+  } else {
+    *unprotected_bytes_size = 0;
+    return TSI_OK;
+  }
+}
+
+static void alts_destroy(tsi_frame_protector* self) {
+  alts_frame_protector* impl = reinterpret_cast<alts_frame_protector*>(self);
+  if (impl != nullptr) {
+    alts_crypter_destroy(impl->seal_crypter);
+    alts_crypter_destroy(impl->unseal_crypter);
+    gpr_free(impl->in_place_protect_buffer);
+    gpr_free(impl->in_place_unprotect_buffer);
+    alts_destroy_frame_writer(impl->writer);
+    alts_destroy_frame_reader(impl->reader);
+    gpr_free(impl);
+  }
+}
+
+static const tsi_frame_protector_vtable alts_frame_protector_vtable = {
+    alts_protect, alts_protect_flush, alts_unprotect, alts_destroy};
+
+static grpc_status_code create_alts_crypters(const uint8_t* key,
+                                             size_t key_size, bool is_client,
+                                             bool is_rekey,
+                                             alts_frame_protector* impl,
+                                             char** error_details) {
+  grpc_status_code status;
+  gsec_aead_crypter* aead_crypter_seal = nullptr;
+  gsec_aead_crypter* aead_crypter_unseal = nullptr;
+  status = gsec_aes_gcm_aead_crypter_create(key, key_size, kAesGcmNonceLength,
+                                            kAesGcmTagLength, is_rekey,
+                                            &aead_crypter_seal, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  status = gsec_aes_gcm_aead_crypter_create(
+      key, key_size, kAesGcmNonceLength, kAesGcmTagLength, is_rekey,
+      &aead_crypter_unseal, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  size_t overflow_size = is_rekey ? kAltsRecordProtocolRekeyFrameLimit
+                                  : kAltsRecordProtocolFrameLimit;
+  status = alts_seal_crypter_create(aead_crypter_seal, is_client, overflow_size,
+                                    &impl->seal_crypter, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  status =
+      alts_unseal_crypter_create(aead_crypter_unseal, is_client, overflow_size,
+                                 &impl->unseal_crypter, error_details);
+  return status;
+}
+
+tsi_result alts_create_frame_protector(const uint8_t* key, size_t key_size,
+                                       bool is_client, bool is_rekey,
+                                       size_t* max_protected_frame_size,
+                                       tsi_frame_protector** self) {
+  if (key == nullptr || self == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to alts_create_frame_protector().");
+    return TSI_INTERNAL_ERROR;
+  }
+  char* error_details = nullptr;
+  alts_frame_protector* impl =
+      static_cast<alts_frame_protector*>(gpr_zalloc(sizeof(*impl)));
+  grpc_status_code status = create_alts_crypters(
+      key, key_size, is_client, is_rekey, impl, &error_details);
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "Failed to create ALTS crypters, %s.", error_details);
+    gpr_free(error_details);
+    return TSI_INTERNAL_ERROR;
+  }
+  /**
+   * Set maximum frame size to be used by a frame protector. If it is nullptr, a
+   * default frame size will be used. Otherwise, the provided frame size will be
+   * adjusted (if not falling into a valid frame range) and used.
+   */
+  size_t max_protected_frame_size_to_set = kDefaultFrameLength;
+  if (max_protected_frame_size != nullptr) {
+    *max_protected_frame_size =
+        GPR_MIN(*max_protected_frame_size, kMaxFrameLength);
+    *max_protected_frame_size =
+        GPR_MAX(*max_protected_frame_size, kMinFrameLength);
+    max_protected_frame_size_to_set = *max_protected_frame_size;
+  }
+  impl->max_protected_frame_size = max_protected_frame_size_to_set;
+  impl->max_unprotected_frame_size = max_protected_frame_size_to_set;
+  impl->in_place_protect_bytes_buffered = 0;
+  impl->in_place_unprotect_bytes_processed = 0;
+  impl->in_place_protect_buffer = static_cast<unsigned char*>(
+      gpr_malloc(sizeof(unsigned char) * max_protected_frame_size_to_set));
+  impl->in_place_unprotect_buffer = static_cast<unsigned char*>(
+      gpr_malloc(sizeof(unsigned char) * max_protected_frame_size_to_set));
+  impl->overhead_length = alts_crypter_num_overhead_bytes(impl->seal_crypter);
+  impl->writer = alts_create_frame_writer();
+  impl->reader = alts_create_frame_reader();
+  impl->base.vtable = &alts_frame_protector_vtable;
+  *self = &impl->base;
+  return TSI_OK;
+}
diff --git a/src/core/tsi/alts/frame_protector/alts_frame_protector.h b/src/core/tsi/alts/frame_protector/alts_frame_protector.h
new file mode 100644
index 0000000000..321bffaed8
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_frame_protector.h
@@ -0,0 +1,55 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_FRAME_PROTECTOR_H
+#define GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_FRAME_PROTECTOR_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stdbool.h>
+
+#include "src/core/tsi/transport_security_interface.h"
+
+typedef struct alts_frame_protector alts_frame_protector;
+
+/**
+ * TODO: Add a parameter to the interface to support the use of
+ * different record protocols within a frame protector.
+ *
+ * This method creates a frame protector.
+ *
+ * - key: a symmetric key used to seal/unseal frames.
+ * - key_size: the size of symmetric key.
+ * - is_client: a flag indicating if the frame protector will be used at client
+ *   (is_client = true) or server (is_client = false) side.
+ * - is_rekey: a flag indicating if the frame protector will use an AEAD with
+ *   rekeying.
+ * - max_protected_frame_size: an in/out parameter indicating max frame size
+ *   to be used by the frame protector. If it is nullptr, the default frame
+ *   size will be used. Otherwise, the provided frame size will be adjusted (if
+ *   not falling into a valid frame range) and used.
+ * - self: a pointer to the frame protector returned from the method.
+ *
+ * This method returns TSI_OK on success and TSI_INTERNAL_ERROR otherwise.
+ */
+tsi_result alts_create_frame_protector(const uint8_t* key, size_t key_size,
+                                       bool is_client, bool is_rekey,
+                                       size_t* max_protected_frame_size,
+                                       tsi_frame_protector** self);
+
+#endif /* GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_FRAME_PROTECTOR_H */
diff --git a/src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.cc b/src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.cc
new file mode 100644
index 0000000000..0574ed5012
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.cc
@@ -0,0 +1,114 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.h"
+
+#include <grpc/support/alloc.h>
+
+static void maybe_copy_error_msg(const char* src, char** dst) {
+  if (dst != nullptr && src != nullptr) {
+    *dst = static_cast<char*>(gpr_malloc(strlen(src) + 1));
+    memcpy(*dst, src, strlen(src) + 1);
+  }
+}
+
+grpc_status_code input_sanity_check(
+    const alts_record_protocol_crypter* rp_crypter, const unsigned char* data,
+    size_t* output_size, char** error_details) {
+  if (rp_crypter == nullptr) {
+    maybe_copy_error_msg("alts_crypter instance is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  } else if (data == nullptr) {
+    maybe_copy_error_msg("data is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  } else if (output_size == nullptr) {
+    maybe_copy_error_msg("output_size is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  return GRPC_STATUS_OK;
+}
+
+grpc_status_code increment_counter(alts_record_protocol_crypter* rp_crypter,
+                                   char** error_details) {
+  bool is_overflow = false;
+  grpc_status_code status =
+      alts_counter_increment(rp_crypter->ctr, &is_overflow, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  if (is_overflow) {
+    const char error_msg[] =
+        "crypter counter is wrapped. The connection"
+        "should be closed and the key should be deleted.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  return GRPC_STATUS_OK;
+}
+
+size_t alts_record_protocol_crypter_num_overhead_bytes(const alts_crypter* c) {
+  if (c != nullptr) {
+    size_t num_overhead_bytes = 0;
+    char* error_details = nullptr;
+    const alts_record_protocol_crypter* rp_crypter =
+        reinterpret_cast<const alts_record_protocol_crypter*>(c);
+    grpc_status_code status = gsec_aead_crypter_tag_length(
+        rp_crypter->crypter, &num_overhead_bytes, &error_details);
+    if (status == GRPC_STATUS_OK) {
+      return num_overhead_bytes;
+    }
+  }
+  return 0;
+}
+
+void alts_record_protocol_crypter_destruct(alts_crypter* c) {
+  if (c != nullptr) {
+    alts_record_protocol_crypter* rp_crypter =
+        reinterpret_cast<alts_record_protocol_crypter*>(c);
+    alts_counter_destroy(rp_crypter->ctr);
+    gsec_aead_crypter_destroy(rp_crypter->crypter);
+  }
+}
+
+alts_record_protocol_crypter* alts_crypter_create_common(
+    gsec_aead_crypter* crypter, bool is_client, size_t overflow_size,
+    char** error_details) {
+  if (crypter != nullptr) {
+    auto* rp_crypter = static_cast<alts_record_protocol_crypter*>(
+        gpr_malloc(sizeof(alts_record_protocol_crypter)));
+    size_t counter_size = 0;
+    grpc_status_code status =
+        gsec_aead_crypter_nonce_length(crypter, &counter_size, error_details);
+    if (status != GRPC_STATUS_OK) {
+      return nullptr;
+    }
+    /* Create a counter. */
+    status = alts_counter_create(is_client, counter_size, overflow_size,
+                                 &rp_crypter->ctr, error_details);
+    if (status != GRPC_STATUS_OK) {
+      return nullptr;
+    }
+    rp_crypter->crypter = crypter;
+    return rp_crypter;
+  }
+  const char error_msg[] = "crypter is nullptr.";
+  maybe_copy_error_msg(error_msg, error_details);
+  return nullptr;
+}
diff --git a/src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.h b/src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.h
new file mode 100644
index 0000000000..682a8f7e7a
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.h
@@ -0,0 +1,114 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_RECORD_PROTOCOL_CRYPTER_COMMON_H
+#define GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_RECORD_PROTOCOL_CRYPTER_COMMON_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/grpc.h>
+
+#include "src/core/tsi/alts/frame_protector/alts_counter.h"
+#include "src/core/tsi/alts/frame_protector/alts_crypter.h"
+
+/**
+ * This file contains common implementation that will be used in both seal and
+ * unseal operations.
+ */
+
+/**
+ * Main struct for alts_record_protocol_crypter that will be used in both
+ * seal and unseal operations.
+ */
+typedef struct alts_record_protocol_crypter {
+  alts_crypter base;
+  gsec_aead_crypter* crypter;
+  alts_counter* ctr;
+} alts_record_protocol_crypter;
+
+/**
+ * This method performs input sanity checks on a subset of inputs to
+ * alts_crypter_process_in_place() for both seal and unseal operations.
+ *
+ * - rp_crypter: an alts_record_protocol_crypter instance.
+ * - data: it represents raw data that needs to be sealed in a seal operation or
+ *   protected data that needs to be unsealed in an unseal operation.
+ * - output_size: size of data written to the data buffer after a seal or
+ *   unseal operation.
+ * - error_details: a buffer containing an error message if any of checked
+ *   inputs is nullptr. It is legal to pass nullptr into error_details and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code input_sanity_check(
+    const alts_record_protocol_crypter* rp_crypter, const unsigned char* data,
+    size_t* output_size, char** error_details);
+
+/**
+ * This method increments the counter within an alts_record_protocol_crypter
+ * instance.
+ *
+ * - rp_crypter: an alts_record_protocol_crypter instance.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly or the counter is wrapped. It is legal to pass nullptr
+ *   into error_details and otherwise, the parameter should be freed with
+ *   gpr_free.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise,
+ * it returns an error status code along with its details specified in
+ * error_details (if error_details is not nullptr).
+ */
+grpc_status_code increment_counter(alts_record_protocol_crypter* rp_crypter,
+                                   char** error_details);
+
+/**
+ * This method creates an alts_crypter instance, and populates the fields
+ * that are common to both seal and unseal operations.
+ *
+ * - crypter: a gsec_aead_crypter instance used to perform AEAD decryption. The
+ *   function does not take ownership of crypter.
+ * - is_client: a flag indicating if the alts_crypter instance will be
+ *   used at the client (is_client = true) or server (is_client =
+ *   false) side.
+ * - overflow_size: overflow size of counter in bytes.
+ * - error_details: a buffer containing an error message if the method does
+ *   not function correctly. It is legal to pass nullptr into error_details, and
+ *   otherwise, the parameter should be freed with gpr_free.
+ *
+ * On success of creation, the method returns alts_record_protocol_crypter
+ * instance. Otherwise, it returns nullptr with its details specified in
+ * error_details (if error_details is not nullptr).
+ *
+ */
+alts_record_protocol_crypter* alts_crypter_create_common(
+    gsec_aead_crypter* crypter, bool is_client, size_t overflow_size,
+    char** error_details);
+
+/**
+ * For the following two methods, please refer to the corresponding API in
+ * alts_crypter.h for detailed specifications.
+ */
+size_t alts_record_protocol_crypter_num_overhead_bytes(const alts_crypter* c);
+
+void alts_record_protocol_crypter_destruct(alts_crypter* c);
+
+#endif /* GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_ALTS_RECORD_PROTOCOL_CRYPTER_COMMON_H \
+        */
diff --git a/src/core/tsi/alts/frame_protector/alts_seal_privacy_integrity_crypter.cc b/src/core/tsi/alts/frame_protector/alts_seal_privacy_integrity_crypter.cc
new file mode 100644
index 0000000000..f407831613
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_seal_privacy_integrity_crypter.cc
@@ -0,0 +1,105 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/support/alloc.h>
+
+#include "src/core/tsi/alts/frame_protector/alts_counter.h"
+#include "src/core/tsi/alts/frame_protector/alts_crypter.h"
+#include "src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.h"
+
+static void maybe_copy_error_msg(const char* src, char** dst) {
+  if (dst != nullptr && src != nullptr) {
+    *dst = static_cast<char*>(gpr_malloc(strlen(src) + 1));
+    memcpy(*dst, src, strlen(src) + 1);
+  }
+}
+
+/* Perform input santity check for a seal operation. */
+static grpc_status_code seal_check(alts_crypter* c, const unsigned char* data,
+                                   size_t data_allocated_size, size_t data_size,
+                                   size_t* output_size, char** error_details) {
+  /* Do common input sanity check. */
+  grpc_status_code status = input_sanity_check(
+      reinterpret_cast<const alts_record_protocol_crypter*>(c), data,
+      output_size, error_details);
+  if (status != GRPC_STATUS_OK) return status;
+  /* Do seal-specific check. */
+  size_t num_overhead_bytes =
+      alts_crypter_num_overhead_bytes(reinterpret_cast<const alts_crypter*>(c));
+  if (data_size == 0) {
+    const char error_msg[] = "data_size is zero.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (data_size + num_overhead_bytes > data_allocated_size) {
+    const char error_msg[] =
+        "data_allocated_size is smaller than sum of data_size and "
+        "num_overhead_bytes.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code alts_seal_crypter_process_in_place(
+    alts_crypter* c, unsigned char* data, size_t data_allocated_size,
+    size_t data_size, size_t* output_size, char** error_details) {
+  grpc_status_code status = seal_check(c, data, data_allocated_size, data_size,
+                                       output_size, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Do AEAD encryption. */
+  alts_record_protocol_crypter* rp_crypter =
+      reinterpret_cast<alts_record_protocol_crypter*>(c);
+  status = gsec_aead_crypter_encrypt(
+      rp_crypter->crypter, alts_counter_get_counter(rp_crypter->ctr),
+      alts_counter_get_size(rp_crypter->ctr), nullptr /* aad */,
+      0 /* aad_length */, data, data_size, data, data_allocated_size,
+      output_size, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Increment the crypter counter. */
+  return increment_counter(rp_crypter, error_details);
+}
+
+static const alts_crypter_vtable vtable = {
+    alts_record_protocol_crypter_num_overhead_bytes,
+    alts_seal_crypter_process_in_place, alts_record_protocol_crypter_destruct};
+
+grpc_status_code alts_seal_crypter_create(gsec_aead_crypter* gc, bool is_client,
+                                          size_t overflow_size,
+                                          alts_crypter** crypter,
+                                          char** error_details) {
+  if (crypter == nullptr) {
+    const char error_msg[] = "crypter is nullptr.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  alts_record_protocol_crypter* rp_crypter =
+      alts_crypter_create_common(gc, !is_client, overflow_size, error_details);
+  if (rp_crypter == nullptr) {
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  rp_crypter->base.vtable = &vtable;
+  *crypter = &rp_crypter->base;
+  return GRPC_STATUS_OK;
+}
diff --git a/src/core/tsi/alts/frame_protector/alts_unseal_privacy_integrity_crypter.cc b/src/core/tsi/alts/frame_protector/alts_unseal_privacy_integrity_crypter.cc
new file mode 100644
index 0000000000..51bea24f1f
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/alts_unseal_privacy_integrity_crypter.cc
@@ -0,0 +1,103 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/support/alloc.h>
+
+#include "src/core/tsi/alts/frame_protector/alts_counter.h"
+#include "src/core/tsi/alts/frame_protector/alts_crypter.h"
+#include "src/core/tsi/alts/frame_protector/alts_record_protocol_crypter_common.h"
+
+static void maybe_copy_error_msg(const char* src, char** dst) {
+  if (dst != nullptr && src != nullptr) {
+    *dst = static_cast<char*>(gpr_malloc(strlen(src) + 1));
+    memcpy(*dst, src, strlen(src) + 1);
+  }
+}
+
+/* Perform input santity check. */
+static grpc_status_code unseal_check(alts_crypter* c, const unsigned char* data,
+                                     size_t data_allocated_size,
+                                     size_t data_size, size_t* output_size,
+                                     char** error_details) {
+  /* Do common input sanity check. */
+  grpc_status_code status = input_sanity_check(
+      reinterpret_cast<const alts_record_protocol_crypter*>(c), data,
+      output_size, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Do unseal-specific input check. */
+  size_t num_overhead_bytes =
+      alts_crypter_num_overhead_bytes(reinterpret_cast<const alts_crypter*>(c));
+  if (num_overhead_bytes > data_size) {
+    const char error_msg[] = "data_size is smaller than num_overhead_bytes.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  return GRPC_STATUS_OK;
+}
+
+static grpc_status_code alts_unseal_crypter_process_in_place(
+    alts_crypter* c, unsigned char* data, size_t data_allocated_size,
+    size_t data_size, size_t* output_size, char** error_details) {
+  grpc_status_code status = unseal_check(c, data, data_allocated_size,
+                                         data_size, output_size, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Do AEAD decryption. */
+  alts_record_protocol_crypter* rp_crypter =
+      reinterpret_cast<alts_record_protocol_crypter*>(c);
+  status = gsec_aead_crypter_decrypt(
+      rp_crypter->crypter, alts_counter_get_counter(rp_crypter->ctr),
+      alts_counter_get_size(rp_crypter->ctr), nullptr /* aad */,
+      0 /* aad_length */, data, data_size, data, data_allocated_size,
+      output_size, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Increment the crypter counter. */
+  return increment_counter(rp_crypter, error_details);
+}
+
+static const alts_crypter_vtable vtable = {
+    alts_record_protocol_crypter_num_overhead_bytes,
+    alts_unseal_crypter_process_in_place,
+    alts_record_protocol_crypter_destruct};
+
+grpc_status_code alts_unseal_crypter_create(gsec_aead_crypter* gc,
+                                            bool is_client,
+                                            size_t overflow_size,
+                                            alts_crypter** crypter,
+                                            char** error_details) {
+  if (crypter == nullptr) {
+    const char error_msg[] = "crypter is nullptr.";
+    maybe_copy_error_msg(error_msg, error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  alts_record_protocol_crypter* rp_crypter =
+      alts_crypter_create_common(gc, is_client, overflow_size, error_details);
+  if (rp_crypter == nullptr) {
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  rp_crypter->base.vtable = &vtable;
+  *crypter = &rp_crypter->base;
+  return GRPC_STATUS_OK;
+}
diff --git a/src/core/tsi/alts/frame_protector/frame_handler.cc b/src/core/tsi/alts/frame_protector/frame_handler.cc
new file mode 100644
index 0000000000..d3fda63b3d
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/frame_handler.cc
@@ -0,0 +1,218 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/frame_protector/frame_handler.h"
+
+#include <limits.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/lib/gpr/useful.h"
+
+/* Use little endian to interpret a string of bytes as uint32_t. */
+static uint32_t load_32_le(const unsigned char* buffer) {
+  return (((uint32_t)buffer[3]) << 24) | (((uint32_t)buffer[2]) << 16) |
+         (((uint32_t)buffer[1]) << 8) | ((uint32_t)buffer[0]);
+}
+
+/* Store uint32_t as a string of little endian bytes. */
+static void store_32_le(uint32_t value, unsigned char* buffer) {
+  buffer[3] = (unsigned char)(value >> 24) & 0xFF;
+  buffer[2] = (unsigned char)(value >> 16) & 0xFF;
+  buffer[1] = (unsigned char)(value >> 8) & 0xFF;
+  buffer[0] = (unsigned char)(value)&0xFF;
+}
+
+/* Frame writer implementation. */
+alts_frame_writer* alts_create_frame_writer() {
+  alts_frame_writer* writer =
+      static_cast<alts_frame_writer*>(gpr_zalloc(sizeof(*writer)));
+  return writer;
+}
+
+bool alts_reset_frame_writer(alts_frame_writer* writer,
+                             const unsigned char* buffer, size_t length) {
+  if (buffer == nullptr) return false;
+  size_t max_input_size = SIZE_MAX - kFrameLengthFieldSize;
+  if (length > max_input_size) {
+    gpr_log(GPR_ERROR, "length must be at most %zu", max_input_size);
+    return false;
+  }
+  writer->input_buffer = buffer;
+  writer->input_size = length;
+  writer->input_bytes_written = 0;
+  writer->header_bytes_written = 0;
+  store_32_le(
+      static_cast<uint32_t>(writer->input_size + kFrameMessageTypeFieldSize),
+      writer->header_buffer);
+  store_32_le(kFrameMessageType, writer->header_buffer + kFrameLengthFieldSize);
+  return true;
+}
+
+bool alts_write_frame_bytes(alts_frame_writer* writer, unsigned char* output,
+                            size_t* bytes_size) {
+  if (bytes_size == nullptr || output == nullptr) return false;
+  if (alts_is_frame_writer_done(writer)) {
+    *bytes_size = 0;
+    return true;
+  }
+  size_t bytes_written = 0;
+  /* Write some header bytes, if needed. */
+  if (writer->header_bytes_written != sizeof(writer->header_buffer)) {
+    size_t bytes_to_write =
+        GPR_MIN(*bytes_size,
+                sizeof(writer->header_buffer) - writer->header_bytes_written);
+    memcpy(output, writer->header_buffer + writer->header_bytes_written,
+           bytes_to_write);
+    bytes_written += bytes_to_write;
+    *bytes_size -= bytes_to_write;
+    writer->header_bytes_written += bytes_to_write;
+    output += bytes_to_write;
+    if (writer->header_bytes_written != sizeof(writer->header_buffer)) {
+      *bytes_size = bytes_written;
+      return true;
+    }
+  }
+  /* Write some non-header bytes. */
+  size_t bytes_to_write =
+      GPR_MIN(writer->input_size - writer->input_bytes_written, *bytes_size);
+  memcpy(output, writer->input_buffer, bytes_to_write);
+  writer->input_buffer += bytes_to_write;
+  bytes_written += bytes_to_write;
+  writer->input_bytes_written += bytes_to_write;
+  *bytes_size = bytes_written;
+  return true;
+}
+
+bool alts_is_frame_writer_done(alts_frame_writer* writer) {
+  return writer->input_buffer == nullptr ||
+         writer->input_size == writer->input_bytes_written;
+}
+
+size_t alts_get_num_writer_bytes_remaining(alts_frame_writer* writer) {
+  return (sizeof(writer->header_buffer) - writer->header_bytes_written) +
+         (writer->input_size - writer->input_bytes_written);
+}
+
+void alts_destroy_frame_writer(alts_frame_writer* writer) { gpr_free(writer); }
+
+/* Frame reader implementation. */
+alts_frame_reader* alts_create_frame_reader() {
+  alts_frame_reader* reader =
+      static_cast<alts_frame_reader*>(gpr_zalloc(sizeof(*reader)));
+  return reader;
+}
+
+bool alts_is_frame_reader_done(alts_frame_reader* reader) {
+  return reader->output_buffer == nullptr ||
+         (reader->header_bytes_read == sizeof(reader->header_buffer) &&
+          reader->bytes_remaining == 0);
+}
+
+bool alts_has_read_frame_length(alts_frame_reader* reader) {
+  return sizeof(reader->header_buffer) == reader->header_bytes_read;
+}
+
+size_t alts_get_reader_bytes_remaining(alts_frame_reader* reader) {
+  return alts_has_read_frame_length(reader) ? reader->bytes_remaining : 0;
+}
+
+void alts_reset_reader_output_buffer(alts_frame_reader* reader,
+                                     unsigned char* buffer) {
+  reader->output_buffer = buffer;
+}
+
+bool alts_reset_frame_reader(alts_frame_reader* reader, unsigned char* buffer) {
+  if (buffer == nullptr) return false;
+  reader->output_buffer = buffer;
+  reader->bytes_remaining = 0;
+  reader->header_bytes_read = 0;
+  reader->output_bytes_read = 0;
+  return true;
+}
+
+bool alts_read_frame_bytes(alts_frame_reader* reader,
+                           const unsigned char* bytes, size_t* bytes_size) {
+  if (bytes_size == nullptr) return false;
+  if (bytes == nullptr) {
+    *bytes_size = 0;
+    return false;
+  }
+  if (alts_is_frame_reader_done(reader)) {
+    *bytes_size = 0;
+    return true;
+  }
+  size_t bytes_processed = 0;
+  /* Process the header, if needed. */
+  if (reader->header_bytes_read != sizeof(reader->header_buffer)) {
+    size_t bytes_to_write = GPR_MIN(
+        *bytes_size, sizeof(reader->header_buffer) - reader->header_bytes_read);
+    memcpy(reader->header_buffer + reader->header_bytes_read, bytes,
+           bytes_to_write);
+    reader->header_bytes_read += bytes_to_write;
+    bytes_processed += bytes_to_write;
+    bytes += bytes_to_write;
+    *bytes_size -= bytes_to_write;
+    if (reader->header_bytes_read != sizeof(reader->header_buffer)) {
+      *bytes_size = bytes_processed;
+      return true;
+    }
+    size_t frame_length = load_32_le(reader->header_buffer);
+    if (frame_length < kFrameMessageTypeFieldSize ||
+        frame_length > kFrameMaxSize) {
+      gpr_log(GPR_ERROR,
+              "Bad frame length (should be at least %zu, and at most %zu)",
+              kFrameMessageTypeFieldSize, kFrameMaxSize);
+      *bytes_size = 0;
+      return false;
+    }
+    size_t message_type =
+        load_32_le(reader->header_buffer + kFrameLengthFieldSize);
+    if (message_type != kFrameMessageType) {
+      gpr_log(GPR_ERROR, "Unsupported message type %zu (should be %zu)",
+              message_type, kFrameMessageType);
+      *bytes_size = 0;
+      return false;
+    }
+    reader->bytes_remaining = frame_length - kFrameMessageTypeFieldSize;
+  }
+  /* Process the non-header bytes. */
+  size_t bytes_to_write = GPR_MIN(*bytes_size, reader->bytes_remaining);
+  memcpy(reader->output_buffer, bytes, bytes_to_write);
+  reader->output_buffer += bytes_to_write;
+  bytes_processed += bytes_to_write;
+  reader->bytes_remaining -= bytes_to_write;
+  reader->output_bytes_read += bytes_to_write;
+  *bytes_size = bytes_processed;
+  return true;
+}
+
+size_t alts_get_output_bytes_read(alts_frame_reader* reader) {
+  return reader->output_bytes_read;
+}
+
+unsigned char* alts_get_output_buffer(alts_frame_reader* reader) {
+  return reader->output_buffer;
+}
+
+void alts_destroy_frame_reader(alts_frame_reader* reader) { gpr_free(reader); }
diff --git a/src/core/tsi/alts/frame_protector/frame_handler.h b/src/core/tsi/alts/frame_protector/frame_handler.h
new file mode 100644
index 0000000000..a703ff40d3
--- /dev/null
+++ b/src/core/tsi/alts/frame_protector/frame_handler.h
@@ -0,0 +1,236 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_FRAME_HANDLER_H
+#define GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_FRAME_HANDLER_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stdbool.h>
+#include <stdlib.h>
+
+const size_t kFrameMessageType = 0x06;
+const size_t kFrameLengthFieldSize = 4;
+const size_t kFrameMessageTypeFieldSize = 4;
+const size_t kFrameMaxSize = 1024 * 1024;
+const size_t kFrameHeaderSize =
+    kFrameLengthFieldSize + kFrameMessageTypeFieldSize;
+
+/**
+ * Implementation of frame reader and frame writer. All APIs in the
+ * header are thread-compatible.
+ */
+
+/**
+ * Main struct for a frame writer. It reads frames from an input buffer, and
+ * writes the contents as raw bytes. It does not own the input buffer.
+ */
+typedef struct alts_frame_writer {
+  const unsigned char* input_buffer;
+  unsigned char header_buffer[kFrameHeaderSize];
+  size_t input_bytes_written;
+  size_t header_bytes_written;
+  size_t input_size;
+} alts_frame_writer;
+
+/**
+ * Main struct for a frame reader. It reads raw bytes and puts the framed
+ * result into an output buffer. It does not own the output buffer.
+ */
+typedef struct alts_frame_reader {
+  unsigned char* output_buffer;
+  unsigned char header_buffer[kFrameHeaderSize];
+  size_t header_bytes_read;
+  size_t output_bytes_read;
+  size_t bytes_remaining;
+} alts_frame_reader;
+
+/**
+ * This method creates a frame writer instance and initializes its internal
+ * states.
+ */
+alts_frame_writer* alts_create_frame_writer();
+
+/**
+ * This method resets internal states of a frame writer and prepares to write
+ * a single frame. It does not take ownership of payload_buffer.
+ * The payload_buffer must outlive the writer.
+ *
+ * - writer: a frame writer instance.
+ * - buffer: a buffer storing full payload data to be framed.
+ * - length: size of payload data.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool alts_reset_frame_writer(alts_frame_writer* writer,
+                             const unsigned char* buffer, size_t length);
+
+/**
+ * This method writes up to bytes_size bytes of a frame to output.
+ *
+ * - writer: a frame writer instance.
+ * - output: an output buffer used to store the frame.
+ * - bytes_size: an in/out parameter that stores the size of output buffer
+ *   before the call, and gets written the number of frame bytes written to the
+ *   buffer.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool alts_write_frame_bytes(alts_frame_writer* writer, unsigned char* output,
+                            size_t* bytes_size);
+
+/**
+ * This method checks if a reset can be called to write a new frame. It returns
+ * true if it's the first time to frame a payload, or the current frame has
+ * been finished processing. It returns false if it's not ready yet to start a
+ * new frame (e.g., more payload data needs to be accumulated to process the
+ * current frame).
+ *
+ * if (alts_is_frame_writer_done(writer)) {
+ *   // a new frame can be written, call reset.
+ *   alts_reset_frame_writer(writer, payload_buffer, payload_size);
+ * } else {
+ *   // accumulate more payload data until a full frame can be written.
+ * }
+ *
+ * - writer: a frame writer instance.
+ */
+bool alts_is_frame_writer_done(alts_frame_writer* writer);
+
+/**
+ * This method returns the number of bytes left to write before a complete frame
+ * is formed.
+ *
+ * - writer: a frame writer instance.
+ */
+size_t alts_get_num_writer_bytes_remaining(alts_frame_writer* writer);
+
+/**
+ * This method destroys a frame writer instance.
+ *
+ * - writer: a frame writer instance.
+ */
+void alts_destroy_frame_writer(alts_frame_writer* writer);
+
+/**
+ * This method creates a frame reader instance and initializes its internal
+ * states.
+ */
+alts_frame_reader* alts_create_frame_reader();
+
+/**
+ * This method resets internal states of a frame reader (including setting its
+ * output_buffer with buffer), and prepares to write processed bytes to
+ * an output_buffer. It does not take ownership of buffer. The buffer must
+ * outlive reader.
+ *
+ * - reader: a frame reader instance.
+ * - buffer: an output buffer used to store deframed results.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool alts_reset_frame_reader(alts_frame_reader* reader, unsigned char* buffer);
+
+/**
+ * This method processes up to the number of bytes given in bytes_size. It may
+ * choose not to process all the bytes, if, for instance, more bytes are
+ * given to the method than required to complete the current frame.
+ *
+ * - reader: a frame reader instance.
+ * - bytes: a buffer that stores data to be processed.
+ * - bytes_size: an in/out parameter that stores the size of bytes before the
+ *   call and gets written the number of bytes processed.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool alts_read_frame_bytes(alts_frame_reader* reader,
+                           const unsigned char* bytes, size_t* bytes_size);
+
+/**
+ * This method checks if a frame length has been read.
+ *
+ * - reader: a frame reader instance.
+ *
+ * The method returns true if a frame length has been read and false otherwise.
+ */
+bool alts_has_read_frame_length(alts_frame_reader* reader);
+
+/**
+ * This method returns the number of bytes the frame reader intends to write.
+ * It may only be called if alts_has_read_frame_length() returns true.
+ *
+ * - reader: a frame reader instance.
+ */
+size_t alts_get_reader_bytes_remaining(alts_frame_reader* reader);
+
+/**
+ * This method resets output_buffer but does not otherwise modify other internal
+ * states of a frame reader instance. After being set, the new output_buffer
+ * will hold the deframed payload held by the original output_buffer. It does
+ * not take ownership of buffer. The buffer must outlive the reader.
+ * To distinguish between two reset methods on a frame reader,
+ *
+ * if (alts_fh_is_frame_reader_done(reader)) {
+ *   // if buffer contains a full payload to be deframed, call reset.
+ *   alts_reset_frame_reader(reader, buffer);
+ * }
+ *
+ * // if remaining buffer space is not enough to hold a full payload
+ * if (buffer_space_remaining < alts_get_reader_bytes_remaining(reader)) {
+ *   // allocate enough space for a new buffer, copy back data processed so far,
+ *   // and call reset.
+ *   alts_reset_reader_output_buffer(reader, new_buffer).
+ * }
+ *
+ * - reader: a frame reader instance.
+ * - buffer: a buffer used to set reader's output_buffer.
+ */
+void alts_reset_reader_output_buffer(alts_frame_reader* reader,
+                                     unsigned char* buffer);
+
+/**
+ * This method checks if reset can be called to start processing a new frame.
+ * If true and reset was previously called, a full frame has been processed and
+ * the content of the frame is available in output_buffer.
+
+ * - reader: a frame reader instance.
+ */
+bool alts_is_frame_reader_done(alts_frame_reader* reader);
+
+/**
+ * This method returns output_bytes_read of a frame reader instance.
+ *
+ * - reader: a frame reader instance.
+ */
+size_t alts_get_output_bytes_read(alts_frame_reader* reader);
+
+/**
+ * This method returns output_buffer of a frame reader instance.
+ *
+ * - reader: a frame reader instance.
+ */
+unsigned char* alts_get_output_buffer(alts_frame_reader* reader);
+
+/**
+ * This method destroys a frame reader instance.
+ *
+ * - reader: a frame reader instance.
+ */
+void alts_destroy_frame_reader(alts_frame_reader* reader);
+
+#endif /* GRPC_CORE_TSI_ALTS_FRAME_PROTECTOR_FRAME_HANDLER_H */
diff --git a/src/core/tsi/alts/handshaker/alts_handshaker_client.cc b/src/core/tsi/alts/handshaker/alts_handshaker_client.cc
new file mode 100644
index 0000000000..40f30e41ca
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_handshaker_client.cc
@@ -0,0 +1,316 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/alts_handshaker_client.h"
+
+#include <grpc/byte_buffer.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/tsi/alts/handshaker/alts_handshaker_service_api.h"
+
+const int kHandshakerClientOpNum = 4;
+
+typedef struct alts_grpc_handshaker_client {
+  alts_handshaker_client base;
+  grpc_call* call;
+  alts_grpc_caller grpc_caller;
+} alts_grpc_handshaker_client;
+
+static grpc_call_error grpc_start_batch(grpc_call* call, const grpc_op* ops,
+                                        size_t nops, void* tag) {
+  return grpc_call_start_batch(call, ops, nops, tag, nullptr);
+}
+
+/**
+ * Populate grpc operation data with the fields of ALTS TSI event and make a
+ * grpc call.
+ */
+static tsi_result make_grpc_call(alts_handshaker_client* client,
+                                 alts_tsi_event* event, bool is_start) {
+  GPR_ASSERT(client != nullptr && event != nullptr);
+  alts_grpc_handshaker_client* grpc_client =
+      reinterpret_cast<alts_grpc_handshaker_client*>(client);
+  grpc_op ops[kHandshakerClientOpNum];
+  memset(ops, 0, sizeof(ops));
+  grpc_op* op = ops;
+  if (is_start) {
+    op->op = GRPC_OP_SEND_INITIAL_METADATA;
+    op->data.send_initial_metadata.count = 0;
+    op++;
+    GPR_ASSERT(op - ops <= kHandshakerClientOpNum);
+    op->op = GRPC_OP_RECV_INITIAL_METADATA;
+    op->data.recv_initial_metadata.recv_initial_metadata =
+        &event->initial_metadata;
+    op++;
+    GPR_ASSERT(op - ops <= kHandshakerClientOpNum);
+  }
+  op->op = GRPC_OP_SEND_MESSAGE;
+  op->data.send_message.send_message = event->send_buffer;
+  op++;
+  GPR_ASSERT(op - ops <= kHandshakerClientOpNum);
+  op->op = GRPC_OP_RECV_MESSAGE;
+  op->data.recv_message.recv_message = &event->recv_buffer;
+  op++;
+  GPR_ASSERT(op - ops <= kHandshakerClientOpNum);
+  GPR_ASSERT(grpc_client->grpc_caller != nullptr);
+  if (grpc_client->grpc_caller(grpc_client->call, ops,
+                               static_cast<size_t>(op - ops),
+                               (void*)event) != GRPC_CALL_OK) {
+    gpr_log(GPR_ERROR, "Start batch operation failed");
+    return TSI_INTERNAL_ERROR;
+  }
+  return TSI_OK;
+}
+
+/* Create and populate a client_start handshaker request, then serialize it. */
+static grpc_byte_buffer* get_serialized_start_client(alts_tsi_event* event) {
+  bool ok = true;
+  grpc_gcp_handshaker_req* req =
+      grpc_gcp_handshaker_req_create(CLIENT_START_REQ);
+  ok &= grpc_gcp_handshaker_req_set_handshake_protocol(
+      req, grpc_gcp_HandshakeProtocol_ALTS);
+  ok &= grpc_gcp_handshaker_req_add_application_protocol(
+      req, ALTS_APPLICATION_PROTOCOL);
+  ok &= grpc_gcp_handshaker_req_add_record_protocol(req, ALTS_RECORD_PROTOCOL);
+  grpc_gcp_rpc_protocol_versions* versions = &event->options->rpc_versions;
+  ok &= grpc_gcp_handshaker_req_set_rpc_versions(
+      req, versions->max_rpc_version.major, versions->max_rpc_version.minor,
+      versions->min_rpc_version.major, versions->min_rpc_version.minor);
+  char* target_name = grpc_slice_to_c_string(event->target_name);
+  ok &= grpc_gcp_handshaker_req_set_target_name(req, target_name);
+  target_service_account* ptr =
+      (reinterpret_cast<grpc_alts_credentials_client_options*>(event->options))
+          ->target_account_list_head;
+  while (ptr != nullptr) {
+    grpc_gcp_handshaker_req_add_target_identity_service_account(req, ptr->data);
+    ptr = ptr->next;
+  }
+  grpc_slice slice;
+  ok &= grpc_gcp_handshaker_req_encode(req, &slice);
+  grpc_byte_buffer* buffer = nullptr;
+  if (ok) {
+    buffer = grpc_raw_byte_buffer_create(&slice, 1 /* number of slices */);
+  }
+  grpc_slice_unref(slice);
+  gpr_free(target_name);
+  grpc_gcp_handshaker_req_destroy(req);
+  return buffer;
+}
+
+static tsi_result handshaker_client_start_client(alts_handshaker_client* client,
+                                                 alts_tsi_event* event) {
+  if (client == nullptr || event == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to alts_grpc_handshaker_client_start_client()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  grpc_byte_buffer* buffer = get_serialized_start_client(event);
+  if (buffer == nullptr) {
+    gpr_log(GPR_ERROR, "get_serialized_start_client() failed");
+    return TSI_INTERNAL_ERROR;
+  }
+  event->send_buffer = buffer;
+  tsi_result result = make_grpc_call(client, event, true /* is_start */);
+  if (result != TSI_OK) {
+    gpr_log(GPR_ERROR, "make_grpc_call() failed");
+  }
+  return result;
+}
+
+/* Create and populate a start_server handshaker request, then serialize it. */
+static grpc_byte_buffer* get_serialized_start_server(
+    alts_tsi_event* event, grpc_slice* bytes_received) {
+  GPR_ASSERT(bytes_received != nullptr);
+  grpc_gcp_handshaker_req* req =
+      grpc_gcp_handshaker_req_create(SERVER_START_REQ);
+  bool ok = grpc_gcp_handshaker_req_add_application_protocol(
+      req, ALTS_APPLICATION_PROTOCOL);
+  ok &= grpc_gcp_handshaker_req_param_add_record_protocol(
+      req, grpc_gcp_HandshakeProtocol_ALTS, ALTS_RECORD_PROTOCOL);
+  ok &= grpc_gcp_handshaker_req_set_in_bytes(
+      req, reinterpret_cast<const char*> GRPC_SLICE_START_PTR(*bytes_received),
+      GRPC_SLICE_LENGTH(*bytes_received));
+  grpc_gcp_rpc_protocol_versions* versions = &event->options->rpc_versions;
+  ok &= grpc_gcp_handshaker_req_set_rpc_versions(
+      req, versions->max_rpc_version.major, versions->max_rpc_version.minor,
+      versions->min_rpc_version.major, versions->min_rpc_version.minor);
+  grpc_slice req_slice;
+  ok &= grpc_gcp_handshaker_req_encode(req, &req_slice);
+  grpc_byte_buffer* buffer = nullptr;
+  if (ok) {
+    buffer = grpc_raw_byte_buffer_create(&req_slice, 1 /* number of slices */);
+  }
+  grpc_slice_unref(req_slice);
+  grpc_gcp_handshaker_req_destroy(req);
+  return buffer;
+}
+
+static tsi_result handshaker_client_start_server(alts_handshaker_client* client,
+                                                 alts_tsi_event* event,
+                                                 grpc_slice* bytes_received) {
+  if (client == nullptr || event == nullptr || bytes_received == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to alts_grpc_handshaker_client_start_server()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  grpc_byte_buffer* buffer = get_serialized_start_server(event, bytes_received);
+  if (buffer == nullptr) {
+    gpr_log(GPR_ERROR, "get_serialized_start_server() failed");
+    return TSI_INTERNAL_ERROR;
+  }
+  event->send_buffer = buffer;
+  tsi_result result = make_grpc_call(client, event, true /* is_start */);
+  if (result != TSI_OK) {
+    gpr_log(GPR_ERROR, "make_grpc_call() failed");
+  }
+  return result;
+}
+
+/* Create and populate a next handshaker request, then serialize it. */
+static grpc_byte_buffer* get_serialized_next(grpc_slice* bytes_received) {
+  GPR_ASSERT(bytes_received != nullptr);
+  grpc_gcp_handshaker_req* req = grpc_gcp_handshaker_req_create(NEXT_REQ);
+  bool ok = grpc_gcp_handshaker_req_set_in_bytes(
+      req, reinterpret_cast<const char*> GRPC_SLICE_START_PTR(*bytes_received),
+      GRPC_SLICE_LENGTH(*bytes_received));
+  grpc_slice req_slice;
+  ok &= grpc_gcp_handshaker_req_encode(req, &req_slice);
+  grpc_byte_buffer* buffer = nullptr;
+  if (ok) {
+    buffer = grpc_raw_byte_buffer_create(&req_slice, 1 /* number of slices */);
+  }
+  grpc_slice_unref(req_slice);
+  grpc_gcp_handshaker_req_destroy(req);
+  return buffer;
+}
+
+static tsi_result handshaker_client_next(alts_handshaker_client* client,
+                                         alts_tsi_event* event,
+                                         grpc_slice* bytes_received) {
+  if (client == nullptr || event == nullptr || bytes_received == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to alts_grpc_handshaker_client_next()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  grpc_byte_buffer* buffer = get_serialized_next(bytes_received);
+  if (buffer == nullptr) {
+    gpr_log(GPR_ERROR, "get_serialized_next() failed");
+    return TSI_INTERNAL_ERROR;
+  }
+  event->send_buffer = buffer;
+  tsi_result result = make_grpc_call(client, event, false /* is_start */);
+  if (result != TSI_OK) {
+    gpr_log(GPR_ERROR, "make_grpc_call() failed");
+  }
+  return result;
+}
+
+static void handshaker_client_destruct(alts_handshaker_client* client) {
+  if (client == nullptr) {
+    return;
+  }
+  alts_grpc_handshaker_client* grpc_client =
+      reinterpret_cast<alts_grpc_handshaker_client*>(client);
+  grpc_call_unref(grpc_client->call);
+}
+
+static const alts_handshaker_client_vtable vtable = {
+    handshaker_client_start_client, handshaker_client_start_server,
+    handshaker_client_next, handshaker_client_destruct};
+
+alts_handshaker_client* alts_grpc_handshaker_client_create(
+    grpc_channel* channel, grpc_completion_queue* queue,
+    const char* handshaker_service_url) {
+  if (channel == nullptr || queue == nullptr ||
+      handshaker_service_url == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid arguments to alts_handshaker_client_create()");
+    return nullptr;
+  }
+  alts_grpc_handshaker_client* client =
+      static_cast<alts_grpc_handshaker_client*>(gpr_zalloc(sizeof(*client)));
+  client->grpc_caller = grpc_start_batch;
+  grpc_slice slice = grpc_slice_from_copied_string(handshaker_service_url);
+  client->call = grpc_channel_create_call(
+      channel, nullptr, GRPC_PROPAGATE_DEFAULTS, queue,
+      grpc_slice_from_static_string(ALTS_SERVICE_METHOD), &slice,
+      gpr_inf_future(GPR_CLOCK_REALTIME), nullptr);
+  client->base.vtable = &vtable;
+  grpc_slice_unref(slice);
+  return &client->base;
+}
+
+namespace grpc_core {
+namespace internal {
+
+void alts_handshaker_client_set_grpc_caller_for_testing(
+    alts_handshaker_client* client, alts_grpc_caller caller) {
+  GPR_ASSERT(client != nullptr && caller != nullptr);
+  alts_grpc_handshaker_client* grpc_client =
+      reinterpret_cast<alts_grpc_handshaker_client*>(client);
+  grpc_client->grpc_caller = caller;
+}
+
+}  // namespace internal
+}  // namespace grpc_core
+
+tsi_result alts_handshaker_client_start_client(alts_handshaker_client* client,
+                                               alts_tsi_event* event) {
+  if (client != nullptr && client->vtable != nullptr &&
+      client->vtable->client_start != nullptr) {
+    return client->vtable->client_start(client, event);
+  }
+  gpr_log(GPR_ERROR,
+          "client or client->vtable has not been initialized properly");
+  return TSI_INVALID_ARGUMENT;
+}
+
+tsi_result alts_handshaker_client_start_server(alts_handshaker_client* client,
+                                               alts_tsi_event* event,
+                                               grpc_slice* bytes_received) {
+  if (client != nullptr && client->vtable != nullptr &&
+      client->vtable->server_start != nullptr) {
+    return client->vtable->server_start(client, event, bytes_received);
+  }
+  gpr_log(GPR_ERROR,
+          "client or client->vtable has not been initialized properly");
+  return TSI_INVALID_ARGUMENT;
+}
+
+tsi_result alts_handshaker_client_next(alts_handshaker_client* client,
+                                       alts_tsi_event* event,
+                                       grpc_slice* bytes_received) {
+  if (client != nullptr && client->vtable != nullptr &&
+      client->vtable->next != nullptr) {
+    return client->vtable->next(client, event, bytes_received);
+  }
+  gpr_log(GPR_ERROR,
+          "client or client->vtable has not been initialized properly");
+  return TSI_INVALID_ARGUMENT;
+}
+
+void alts_handshaker_client_destroy(alts_handshaker_client* client) {
+  if (client != nullptr) {
+    if (client->vtable != nullptr && client->vtable->destruct != nullptr) {
+      client->vtable->destruct(client);
+    }
+    gpr_free(client);
+  }
+}
diff --git a/src/core/tsi/alts/handshaker/alts_handshaker_client.h b/src/core/tsi/alts/handshaker/alts_handshaker_client.h
new file mode 100644
index 0000000000..fb2d2cf68e
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_handshaker_client.h
@@ -0,0 +1,137 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_CLIENT_H
+#define GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_CLIENT_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/grpc.h>
+
+#include "src/core/tsi/alts/handshaker/alts_tsi_event.h"
+
+#define ALTS_SERVICE_METHOD "/grpc.gcp.HandshakerService/DoHandshake"
+#define ALTS_APPLICATION_PROTOCOL "grpc"
+#define ALTS_RECORD_PROTOCOL "ALTSRP_GCM_AES128_REKEY"
+
+const size_t kAltsAes128GcmRekeyKeyLength = 44;
+
+/**
+ * A ALTS handshaker client interface. It is used to communicate with
+ * ALTS handshaker service by scheduling a handshaker request that could be one
+ * of client_start, server_start, and next handshaker requests. All APIs in the
+ * header are thread-compatible.
+ */
+typedef struct alts_handshaker_client alts_handshaker_client;
+
+/* A function that makes the grpc call to the handshaker service. */
+typedef grpc_call_error (*alts_grpc_caller)(grpc_call* call, const grpc_op* ops,
+                                            size_t nops, void* tag);
+
+/* V-table for ALTS handshaker client operations. */
+typedef struct alts_handshaker_client_vtable {
+  tsi_result (*client_start)(alts_handshaker_client* client,
+                             alts_tsi_event* event);
+  tsi_result (*server_start)(alts_handshaker_client* client,
+                             alts_tsi_event* event, grpc_slice* bytes_received);
+  tsi_result (*next)(alts_handshaker_client* client, alts_tsi_event* event,
+                     grpc_slice* bytes_received);
+  void (*destruct)(alts_handshaker_client* client);
+} alts_handshaker_client_vtable;
+
+struct alts_handshaker_client {
+  const alts_handshaker_client_vtable* vtable;
+};
+
+/**
+ * This method schedules a client_start handshaker request to ALTS handshaker
+ * service.
+ *
+ * - client: ALTS handshaker client instance.
+ * - event: ALTS TSI event instance.
+ *
+ * It returns TSI_OK on success and an error status code on failure.
+ */
+tsi_result alts_handshaker_client_start_client(alts_handshaker_client* client,
+                                               alts_tsi_event* event);
+
+/**
+ * This method schedules a server_start handshaker request to ALTS handshaker
+ * service.
+ *
+ * - client: ALTS handshaker client instance.
+ * - event: ALTS TSI event instance.
+ * - bytes_received: bytes in out_frames returned from the peer's handshaker
+ *   response.
+ *
+ * It returns TSI_OK on success and an error status code on failure.
+ */
+tsi_result alts_handshaker_client_start_server(alts_handshaker_client* client,
+                                               alts_tsi_event* event,
+                                               grpc_slice* bytes_received);
+
+/**
+ * This method schedules a next handshaker request to ALTS handshaker service.
+ *
+ * - client: ALTS handshaker client instance.
+ * - event: ALTS TSI event instance.
+ * - bytes_received: bytes in out_frames returned from the peer's handshaker
+ *   response.
+ *
+ * It returns TSI_OK on success and an error status code on failure.
+ */
+tsi_result alts_handshaker_client_next(alts_handshaker_client* client,
+                                       alts_tsi_event* event,
+                                       grpc_slice* bytes_received);
+
+/**
+ * This method destroys a ALTS handshaker client.
+ *
+ * - client: a ALTS handshaker client instance.
+ */
+void alts_handshaker_client_destroy(alts_handshaker_client* client);
+
+/**
+ * This method creates a ALTS handshaker client.
+ *
+ * - channel: grpc channel to ALTS handshaker service.
+ * - queue: grpc completion queue.
+ * - handshaker_service_url: address of ALTS handshaker service in the format of
+ *   "host:port".
+ *
+ * It returns the created ALTS handshaker client on success, and NULL on
+ * failure.
+ */
+alts_handshaker_client* alts_grpc_handshaker_client_create(
+    grpc_channel* channel, grpc_completion_queue* queue,
+    const char* handshaker_service_url);
+
+namespace grpc_core {
+namespace internal {
+
+/**
+ * Unsafe, use for testing only. It allows the caller to change the way that
+ * GRPC calls are made to the handshaker service.
+ */
+void alts_handshaker_client_set_grpc_caller_for_testing(
+    alts_handshaker_client* client, alts_grpc_caller caller);
+
+}  // namespace internal
+}  // namespace grpc_core
+
+#endif /* GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_CLIENT_H */
diff --git a/src/core/tsi/alts/handshaker/alts_handshaker_service_api.cc b/src/core/tsi/alts/handshaker/alts_handshaker_service_api.cc
new file mode 100644
index 0000000000..256e414ae4
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_handshaker_service_api.cc
@@ -0,0 +1,520 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/alts_handshaker_service_api.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "src/core/tsi/alts/handshaker/transport_security_common_api.h"
+
+/* HandshakerReq */
+grpc_gcp_handshaker_req* grpc_gcp_handshaker_req_create(
+    grpc_gcp_handshaker_req_type type) {
+  grpc_gcp_handshaker_req* req =
+      static_cast<grpc_gcp_handshaker_req*>(gpr_zalloc(sizeof(*req)));
+  switch (type) {
+    case CLIENT_START_REQ:
+      req->has_client_start = true;
+      break;
+    case SERVER_START_REQ:
+      req->has_server_start = true;
+      break;
+    case NEXT_REQ:
+      req->has_next = true;
+      break;
+  }
+  return req;
+}
+
+void grpc_gcp_handshaker_req_destroy(grpc_gcp_handshaker_req* req) {
+  if (req == nullptr) {
+    return;
+  }
+  if (req->has_client_start) {
+    /* Destroy client_start request. */
+    destroy_repeated_field_list_identity(
+        static_cast<repeated_field*>(req->client_start.target_identities.arg));
+    destroy_repeated_field_list_string(static_cast<repeated_field*>(
+        req->client_start.application_protocols.arg));
+    destroy_repeated_field_list_string(
+        static_cast<repeated_field*>(req->client_start.record_protocols.arg));
+    if (req->client_start.has_local_identity) {
+      destroy_slice(static_cast<grpc_slice*>(
+          req->client_start.local_identity.hostname.arg));
+      destroy_slice(static_cast<grpc_slice*>(
+          req->client_start.local_identity.service_account.arg));
+    }
+    if (req->client_start.has_local_endpoint) {
+      destroy_slice(static_cast<grpc_slice*>(
+          req->client_start.local_endpoint.ip_address.arg));
+    }
+    if (req->client_start.has_remote_endpoint) {
+      destroy_slice(static_cast<grpc_slice*>(
+          req->client_start.remote_endpoint.ip_address.arg));
+    }
+    destroy_slice(static_cast<grpc_slice*>(req->client_start.target_name.arg));
+  } else if (req->has_server_start) {
+    /* Destroy server_start request. */
+    size_t i = 0;
+    for (i = 0; i < req->server_start.handshake_parameters_count; i++) {
+      destroy_repeated_field_list_identity(
+          static_cast<repeated_field*>(req->server_start.handshake_parameters[i]
+                                           .value.local_identities.arg));
+      destroy_repeated_field_list_string(
+          static_cast<repeated_field*>(req->server_start.handshake_parameters[i]
+                                           .value.record_protocols.arg));
+    }
+    destroy_repeated_field_list_string(static_cast<repeated_field*>(
+        req->server_start.application_protocols.arg));
+    if (req->server_start.has_local_endpoint) {
+      destroy_slice(static_cast<grpc_slice*>(
+          req->server_start.local_endpoint.ip_address.arg));
+    }
+    if (req->server_start.has_remote_endpoint) {
+      destroy_slice(static_cast<grpc_slice*>(
+          req->server_start.remote_endpoint.ip_address.arg));
+    }
+    destroy_slice(static_cast<grpc_slice*>(req->server_start.in_bytes.arg));
+  } else {
+    /* Destroy next request. */
+    destroy_slice(static_cast<grpc_slice*>(req->next.in_bytes.arg));
+  }
+  gpr_free(req);
+}
+
+bool grpc_gcp_handshaker_req_set_handshake_protocol(
+    grpc_gcp_handshaker_req* req,
+    grpc_gcp_handshake_protocol handshake_protocol) {
+  if (req == nullptr || !req->has_client_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_set_handshake_protocol().");
+    return false;
+  }
+  req->client_start.has_handshake_security_protocol = true;
+  req->client_start.handshake_security_protocol = handshake_protocol;
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_set_target_name(grpc_gcp_handshaker_req* req,
+                                             const char* target_name) {
+  if (req == nullptr || target_name == nullptr || !req->has_client_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_set_target_name().");
+    return false;
+  }
+  grpc_slice* slice = create_slice(target_name, strlen(target_name));
+  req->client_start.target_name.arg = slice;
+  req->client_start.target_name.funcs.encode = encode_string_or_bytes_cb;
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_add_application_protocol(
+    grpc_gcp_handshaker_req* req, const char* application_protocol) {
+  if (req == nullptr || application_protocol == nullptr || req->has_next) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_add_application_protocol().");
+    return false;
+  }
+  grpc_slice* slice =
+      create_slice(application_protocol, strlen(application_protocol));
+  if (req->has_client_start) {
+    add_repeated_field(reinterpret_cast<repeated_field**>(
+                           &req->client_start.application_protocols.arg),
+                       slice);
+    req->client_start.application_protocols.funcs.encode =
+        encode_repeated_string_cb;
+  } else {
+    add_repeated_field(reinterpret_cast<repeated_field**>(
+                           &req->server_start.application_protocols.arg),
+                       slice);
+    req->server_start.application_protocols.funcs.encode =
+        encode_repeated_string_cb;
+  }
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_add_record_protocol(grpc_gcp_handshaker_req* req,
+                                                 const char* record_protocol) {
+  if (req == nullptr || record_protocol == nullptr || !req->has_client_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_add_record_protocol().");
+    return false;
+  }
+  grpc_slice* slice = create_slice(record_protocol, strlen(record_protocol));
+  add_repeated_field(reinterpret_cast<repeated_field**>(
+                         &req->client_start.record_protocols.arg),
+                     slice);
+  req->client_start.record_protocols.funcs.encode = encode_repeated_string_cb;
+  return true;
+}
+
+static void set_identity_hostname(grpc_gcp_identity* identity,
+                                  const char* hostname) {
+  grpc_slice* slice = create_slice(hostname, strlen(hostname));
+  identity->hostname.arg = slice;
+  identity->hostname.funcs.encode = encode_string_or_bytes_cb;
+}
+
+static void set_identity_service_account(grpc_gcp_identity* identity,
+                                         const char* service_account) {
+  grpc_slice* slice = create_slice(service_account, strlen(service_account));
+  identity->service_account.arg = slice;
+  identity->service_account.funcs.encode = encode_string_or_bytes_cb;
+}
+
+bool grpc_gcp_handshaker_req_add_target_identity_hostname(
+    grpc_gcp_handshaker_req* req, const char* hostname) {
+  if (req == nullptr || hostname == nullptr || !req->has_client_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to "
+            "grpc_gcp_handshaker_req_add_target_identity_hostname().");
+    return false;
+  }
+  grpc_gcp_identity* target_identity =
+      static_cast<grpc_gcp_identity*>(gpr_zalloc(sizeof(*target_identity)));
+  set_identity_hostname(target_identity, hostname);
+  req->client_start.target_identities.funcs.encode =
+      encode_repeated_identity_cb;
+  add_repeated_field(reinterpret_cast<repeated_field**>(
+                         &req->client_start.target_identities.arg),
+                     target_identity);
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_add_target_identity_service_account(
+    grpc_gcp_handshaker_req* req, const char* service_account) {
+  if (req == nullptr || service_account == nullptr || !req->has_client_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to "
+            "grpc_gcp_handshaker_req_add_target_identity_service_account().");
+    return false;
+  }
+  grpc_gcp_identity* target_identity =
+      static_cast<grpc_gcp_identity*>(gpr_zalloc(sizeof(*target_identity)));
+  set_identity_service_account(target_identity, service_account);
+  req->client_start.target_identities.funcs.encode =
+      encode_repeated_identity_cb;
+  add_repeated_field(reinterpret_cast<repeated_field**>(
+                         &req->client_start.target_identities.arg),
+                     target_identity);
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_set_local_identity_hostname(
+    grpc_gcp_handshaker_req* req, const char* hostname) {
+  if (req == nullptr || hostname == nullptr || !req->has_client_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to "
+            "grpc_gcp_handshaker_req_set_local_identity_hostname().");
+    return false;
+  }
+  req->client_start.has_local_identity = true;
+  set_identity_hostname(&req->client_start.local_identity, hostname);
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_set_local_identity_service_account(
+    grpc_gcp_handshaker_req* req, const char* service_account) {
+  if (req == nullptr || service_account == nullptr || !req->has_client_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to "
+            "grpc_gcp_handshaker_req_set_local_identity_service_account().");
+    return false;
+  }
+  req->client_start.has_local_identity = true;
+  set_identity_service_account(&req->client_start.local_identity,
+                               service_account);
+  return true;
+}
+
+static void set_endpoint(grpc_gcp_endpoint* endpoint, const char* ip_address,
+                         size_t port, grpc_gcp_network_protocol protocol) {
+  grpc_slice* slice = create_slice(ip_address, strlen(ip_address));
+  endpoint->ip_address.arg = slice;
+  endpoint->ip_address.funcs.encode = encode_string_or_bytes_cb;
+  endpoint->has_port = true;
+  endpoint->port = static_cast<int32_t>(port);
+  endpoint->has_protocol = true;
+  endpoint->protocol = protocol;
+}
+
+bool grpc_gcp_handshaker_req_set_rpc_versions(grpc_gcp_handshaker_req* req,
+                                              uint32_t max_major,
+                                              uint32_t max_minor,
+                                              uint32_t min_major,
+                                              uint32_t min_minor) {
+  if (req == nullptr || req->has_next) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_set_rpc_versions().");
+    return false;
+  }
+  if (req->has_client_start) {
+    req->client_start.has_rpc_versions = true;
+    grpc_gcp_rpc_protocol_versions_set_max(&req->client_start.rpc_versions,
+                                           max_major, max_minor);
+    grpc_gcp_rpc_protocol_versions_set_min(&req->client_start.rpc_versions,
+                                           min_major, min_minor);
+  } else {
+    req->server_start.has_rpc_versions = true;
+    grpc_gcp_rpc_protocol_versions_set_max(&req->server_start.rpc_versions,
+                                           max_major, max_minor);
+    grpc_gcp_rpc_protocol_versions_set_min(&req->server_start.rpc_versions,
+                                           min_major, min_minor);
+  }
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_set_local_endpoint(
+    grpc_gcp_handshaker_req* req, const char* ip_address, size_t port,
+    grpc_gcp_network_protocol protocol) {
+  if (req == nullptr || ip_address == nullptr || port > 65535 ||
+      req->has_next) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_set_local_endpoint().");
+    return false;
+  }
+  if (req->has_client_start) {
+    req->client_start.has_local_endpoint = true;
+    set_endpoint(&req->client_start.local_endpoint, ip_address, port, protocol);
+  } else {
+    req->server_start.has_local_endpoint = true;
+    set_endpoint(&req->server_start.local_endpoint, ip_address, port, protocol);
+  }
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_set_remote_endpoint(
+    grpc_gcp_handshaker_req* req, const char* ip_address, size_t port,
+    grpc_gcp_network_protocol protocol) {
+  if (req == nullptr || ip_address == nullptr || port > 65535 ||
+      req->has_next) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_set_remote_endpoint().");
+    return false;
+  }
+  if (req->has_client_start) {
+    req->client_start.has_remote_endpoint = true;
+    set_endpoint(&req->client_start.remote_endpoint, ip_address, port,
+                 protocol);
+  } else {
+    req->server_start.has_remote_endpoint = true;
+    set_endpoint(&req->server_start.remote_endpoint, ip_address, port,
+                 protocol);
+  }
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_set_in_bytes(grpc_gcp_handshaker_req* req,
+                                          const char* in_bytes, size_t size) {
+  if (req == nullptr || in_bytes == nullptr || req->has_client_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_set_in_bytes().");
+    return false;
+  }
+  grpc_slice* slice = create_slice(in_bytes, size);
+  if (req->has_next) {
+    req->next.in_bytes.arg = slice;
+    req->next.in_bytes.funcs.encode = &encode_string_or_bytes_cb;
+  } else {
+    req->server_start.in_bytes.arg = slice;
+    req->server_start.in_bytes.funcs.encode = &encode_string_or_bytes_cb;
+  }
+  return true;
+}
+
+static grpc_gcp_server_handshake_parameters* server_start_find_param(
+    grpc_gcp_handshaker_req* req, int32_t key) {
+  size_t i = 0;
+  for (i = 0; i < req->server_start.handshake_parameters_count; i++) {
+    if (req->server_start.handshake_parameters[i].key == key) {
+      return &req->server_start.handshake_parameters[i].value;
+    }
+  }
+  req->server_start
+      .handshake_parameters[req->server_start.handshake_parameters_count]
+      .has_key = true;
+  req->server_start
+      .handshake_parameters[req->server_start.handshake_parameters_count]
+      .has_value = true;
+  req->server_start
+      .handshake_parameters[req->server_start.handshake_parameters_count++]
+      .key = key;
+  return &req->server_start
+              .handshake_parameters
+                  [req->server_start.handshake_parameters_count - 1]
+              .value;
+}
+
+bool grpc_gcp_handshaker_req_param_add_record_protocol(
+    grpc_gcp_handshaker_req* req, grpc_gcp_handshake_protocol key,
+    const char* record_protocol) {
+  if (req == nullptr || record_protocol == nullptr || !req->has_server_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_param_add_record_protocol().");
+    return false;
+  }
+  grpc_gcp_server_handshake_parameters* param =
+      server_start_find_param(req, key);
+  grpc_slice* slice = create_slice(record_protocol, strlen(record_protocol));
+  add_repeated_field(
+      reinterpret_cast<repeated_field**>(&param->record_protocols.arg), slice);
+  param->record_protocols.funcs.encode = &encode_repeated_string_cb;
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_param_add_local_identity_hostname(
+    grpc_gcp_handshaker_req* req, grpc_gcp_handshake_protocol key,
+    const char* hostname) {
+  if (req == nullptr || hostname == nullptr || !req->has_server_start) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_handshaker_req_param_add_local_identity_hostname().");
+    return false;
+  }
+  grpc_gcp_server_handshake_parameters* param =
+      server_start_find_param(req, key);
+  grpc_gcp_identity* local_identity =
+      static_cast<grpc_gcp_identity*>(gpr_zalloc(sizeof(*local_identity)));
+  set_identity_hostname(local_identity, hostname);
+  add_repeated_field(
+      reinterpret_cast<repeated_field**>(&param->local_identities.arg),
+      local_identity);
+  param->local_identities.funcs.encode = &encode_repeated_identity_cb;
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_param_add_local_identity_service_account(
+    grpc_gcp_handshaker_req* req, grpc_gcp_handshake_protocol key,
+    const char* service_account) {
+  if (req == nullptr || service_account == nullptr || !req->has_server_start) {
+    gpr_log(
+        GPR_ERROR,
+        "Invalid arguments to "
+        "grpc_gcp_handshaker_req_param_add_local_identity_service_account().");
+    return false;
+  }
+  grpc_gcp_server_handshake_parameters* param =
+      server_start_find_param(req, key);
+  grpc_gcp_identity* local_identity =
+      static_cast<grpc_gcp_identity*>(gpr_zalloc(sizeof(*local_identity)));
+  set_identity_service_account(local_identity, service_account);
+  add_repeated_field(
+      reinterpret_cast<repeated_field**>(&param->local_identities.arg),
+      local_identity);
+  param->local_identities.funcs.encode = &encode_repeated_identity_cb;
+  return true;
+}
+
+bool grpc_gcp_handshaker_req_encode(grpc_gcp_handshaker_req* req,
+                                    grpc_slice* slice) {
+  if (req == nullptr || slice == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to grpc_gcp_handshaker_req_encode().");
+    return false;
+  }
+  pb_ostream_t size_stream;
+  memset(&size_stream, 0, sizeof(pb_ostream_t));
+  if (!pb_encode(&size_stream, grpc_gcp_HandshakerReq_fields, req)) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&size_stream));
+    return false;
+  }
+  size_t encoded_length = size_stream.bytes_written;
+  *slice = grpc_slice_malloc(encoded_length);
+  pb_ostream_t output_stream =
+      pb_ostream_from_buffer(GRPC_SLICE_START_PTR(*slice), encoded_length);
+  if (!pb_encode(&output_stream, grpc_gcp_HandshakerReq_fields, req) != 0) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&output_stream));
+    return false;
+  }
+  return true;
+}
+
+/* HandshakerResp. */
+grpc_gcp_handshaker_resp* grpc_gcp_handshaker_resp_create(void) {
+  grpc_gcp_handshaker_resp* resp =
+      static_cast<grpc_gcp_handshaker_resp*>(gpr_zalloc(sizeof(*resp)));
+  return resp;
+}
+
+void grpc_gcp_handshaker_resp_destroy(grpc_gcp_handshaker_resp* resp) {
+  if (resp != nullptr) {
+    destroy_slice(static_cast<grpc_slice*>(resp->out_frames.arg));
+    if (resp->has_status) {
+      destroy_slice(static_cast<grpc_slice*>(resp->status.details.arg));
+    }
+    if (resp->has_result) {
+      destroy_slice(
+          static_cast<grpc_slice*>(resp->result.application_protocol.arg));
+      destroy_slice(static_cast<grpc_slice*>(resp->result.record_protocol.arg));
+      destroy_slice(static_cast<grpc_slice*>(resp->result.key_data.arg));
+      if (resp->result.has_local_identity) {
+        destroy_slice(
+            static_cast<grpc_slice*>(resp->result.local_identity.hostname.arg));
+        destroy_slice(static_cast<grpc_slice*>(
+            resp->result.local_identity.service_account.arg));
+      }
+      if (resp->result.has_peer_identity) {
+        destroy_slice(
+            static_cast<grpc_slice*>(resp->result.peer_identity.hostname.arg));
+        destroy_slice(static_cast<grpc_slice*>(
+            resp->result.peer_identity.service_account.arg));
+      }
+    }
+    gpr_free(resp);
+  }
+}
+
+bool grpc_gcp_handshaker_resp_decode(grpc_slice encoded_handshaker_resp,
+                                     grpc_gcp_handshaker_resp* resp) {
+  if (resp == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr argument to grpc_gcp_handshaker_resp_decode().");
+    return false;
+  }
+  pb_istream_t stream =
+      pb_istream_from_buffer(GRPC_SLICE_START_PTR(encoded_handshaker_resp),
+                             GRPC_SLICE_LENGTH(encoded_handshaker_resp));
+  resp->out_frames.funcs.decode = decode_string_or_bytes_cb;
+  resp->status.details.funcs.decode = decode_string_or_bytes_cb;
+  resp->result.application_protocol.funcs.decode = decode_string_or_bytes_cb;
+  resp->result.record_protocol.funcs.decode = decode_string_or_bytes_cb;
+  resp->result.key_data.funcs.decode = decode_string_or_bytes_cb;
+  resp->result.peer_identity.hostname.funcs.decode = decode_string_or_bytes_cb;
+  resp->result.peer_identity.service_account.funcs.decode =
+      decode_string_or_bytes_cb;
+  resp->result.local_identity.hostname.funcs.decode = decode_string_or_bytes_cb;
+  resp->result.local_identity.service_account.funcs.decode =
+      decode_string_or_bytes_cb;
+  if (!pb_decode(&stream, grpc_gcp_HandshakerResp_fields, resp)) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
+    return false;
+  }
+  return true;
+}
diff --git a/src/core/tsi/alts/handshaker/alts_handshaker_service_api.h b/src/core/tsi/alts/handshaker/alts_handshaker_service_api.h
new file mode 100644
index 0000000000..5df56a86fa
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_handshaker_service_api.h
@@ -0,0 +1,323 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_SERVICE_API_H
+#define GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_SERVICE_API_H
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/alts_handshaker_service_api_util.h"
+
+/**
+ * An implementation of nanopb thin wrapper used to set/get and
+ * serialize/de-serialize of ALTS handshake requests and responses.
+ *
+ * All APIs in the header are thread-compatible. A typical usage of this API at
+ * the client side is as follows:
+ *
+ * -----------------------------------------------------------------------------
+ * // Create, populate, and serialize an ALTS client_start handshake request to
+ * // send to the server.
+ * grpc_gcp_handshaker_req* req =
+ *     grpc_gcp_handshaker_req_create(CLIENT_START_REQ);
+ * grpc_gcp_handshaker_req_set_handshake_protocol(
+       req, grpc_gcp_HandshakeProtocol_ALTS);
+ * grpc_gcp_handshaker_req_add_application_protocol(req, "grpc");
+ * grpc_gcp_handshaker_req_add_record_protocol(req, "ALTSRP_GCM_AES128");
+ * grpc_slice client_slice;
+ * if (!grpc_gcp_handshaker_req_encode(req, &client_slice)) {
+ *   fprintf(stderr, "ALTS handshake request encoding failed.";
+ * }
+ *
+ * // De-serialize a data stream received from the server, and store the result
+ * // at ALTS handshake response.
+ * grpc_gcp_handshaker_resp* resp = grpc_gcp_handshaker_resp_create();
+ * if (!grpc_gcp_handshaker_resp_decode(server_slice, resp)) {
+ *    fprintf(stderr, "ALTS handshake response decoding failed.");
+ * }
+ * // To access a variable-length datatype field (i.e., pb_callback_t),
+ * // access its "arg" subfield (if it has been set).
+ * if (resp->out_frames.arg != nullptr) {
+ *   grpc_slice* slice = resp->out_frames.arg;
+ * }
+ * // To access a fixed-length datatype field (i.e., not pb_calback_t),
+ * // access the field directly (if it has been set).
+ * if (resp->has_status && resp->status->has_code) {
+ *   uint32_t code = resp->status->code;
+ * }
+ *------------------------------------------------------------------------------
+ */
+
+/**
+ * This method creates an ALTS handshake request.
+ *
+ * - type: an enum type value that can be either CLIENT_START_REQ,
+ *   SERVER_START_REQ, or NEXT_REQ to indicate the created instance will be
+ *   client_start, server_start, and next handshake request message
+ * respectively.
+ *
+ * The method returns a pointer to the created instance.
+ */
+grpc_gcp_handshaker_req* grpc_gcp_handshaker_req_create(
+    grpc_gcp_handshaker_req_type type);
+
+/**
+ * This method sets the value for handshake_security_protocol field of ALTS
+ * client_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - handshake_protocol: a enum type value representing the handshake security
+ *   protocol.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_set_handshake_protocol(
+    grpc_gcp_handshaker_req* req,
+    grpc_gcp_handshake_protocol handshake_protocol);
+
+/**
+ * This method sets the value for target_name field of ALTS client_start
+ * handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - target_name: a target name to be set.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_set_target_name(grpc_gcp_handshaker_req* req,
+                                             const char* target_name);
+
+/**
+ * This method adds an application protocol supported by the server (or
+ * client) to ALTS server_start (or client_start) handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - application_protocol: an application protocol (e.g., grpc) to be added.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_add_application_protocol(
+    grpc_gcp_handshaker_req* req, const char* application_protocol);
+
+/**
+ * This method adds a record protocol supported by the client to ALTS
+ * client_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - record_protocol: a record protocol (e.g., ALTSRP_GCM_AES128) to be
+ *   added.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_add_record_protocol(grpc_gcp_handshaker_req* req,
+                                                 const char* record_protocol);
+
+/**
+ * This method adds a target server identity represented as hostname and
+ * acceptable by a client to ALTS client_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - hostname: a string representation of hostname at the connection
+ *   endpoint to be added.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_add_target_identity_hostname(
+    grpc_gcp_handshaker_req* req, const char* hostname);
+
+/**
+ * This method adds a target server identity represented as service account and
+ * acceptable by a client to ALTS client_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - service_account: a string representation of service account at the
+ *   connection endpoint to be added.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_add_target_identity_service_account(
+    grpc_gcp_handshaker_req* req, const char* service_account);
+
+/**
+ * This method sets the hostname for local_identity field of ALTS client_start
+ * handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - hostname: a string representation of hostname.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_set_local_identity_hostname(
+    grpc_gcp_handshaker_req* req, const char* hostname);
+
+/**
+ * This method sets the service account for local_identity field of ALTS
+ * client_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - service_account: a string representation of service account.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_set_local_identity_service_account(
+    grpc_gcp_handshaker_req* req, const char* service_account);
+
+/**
+ * This method sets the value for local_endpoint field of either ALTS
+ * client_start or server_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - ip_address: a string representation of ip address associated with the
+ *   local endpoint, that could be either IPv4 or IPv6.
+ * - port: a port number associated with the local endpoint.
+ * - protocol: a network protocol (e.g., TCP or UDP) associated with the
+ *   local endpoint.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_set_local_endpoint(
+    grpc_gcp_handshaker_req* req, const char* ip_address, size_t port,
+    grpc_gcp_network_protocol protocol);
+
+/**
+ * This method sets the value for remote_endpoint field of either ALTS
+ * client_start or server_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - ip_address: a string representation of ip address associated with the
+ *   remote endpoint, that could be either IPv4 or IPv6.
+ * - port: a port number associated with the remote endpoint.
+ * - protocol: a network protocol (e.g., TCP or UDP) associated with the
+ *   remote endpoint.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_set_remote_endpoint(
+    grpc_gcp_handshaker_req* req, const char* ip_address, size_t port,
+    grpc_gcp_network_protocol protocol);
+
+/**
+ * This method sets the value for in_bytes field of either ALTS server_start or
+ * next handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - in_bytes: a buffer containing bytes taken from out_frames of the peer's
+ *   ALTS handshake response. It is possible that the peer's out_frames are
+ * split into multiple handshake request messages.
+ * - size: size of in_bytes buffer.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_set_in_bytes(grpc_gcp_handshaker_req* req,
+                                          const char* in_bytes, size_t size);
+
+/**
+ * This method adds a record protocol to handshake parameters mapped by the
+ * handshake protocol for ALTS server_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - key: an enum type value representing a handshake security protocol.
+ * - record_protocol: a record protocol to be added.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_param_add_record_protocol(
+    grpc_gcp_handshaker_req* req, grpc_gcp_handshake_protocol key,
+    const char* record_protocol);
+
+/**
+ * This method adds a local identity represented as hostname to handshake
+ * parameters mapped by the handshake protocol for ALTS server_start handshake
+ * request.
+ *
+ * - req: an ALTS handshake request.
+ * - key: an enum type value representing a handshake security protocol.
+ * - hostname: a string representation of hostname to be added.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_param_add_local_identity_hostname(
+    grpc_gcp_handshaker_req* req, grpc_gcp_handshake_protocol key,
+    const char* hostname);
+
+/**
+ * This method adds a local identity represented as service account to handshake
+ * parameters mapped by the handshake protocol for ALTS server_start handshake
+ * request.
+ *
+ * - req: an ALTS handshake request.
+ * - key: an enum type value representing a handshake security protocol.
+ * - service_account: a string representation of service account to be added.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_param_add_local_identity_service_account(
+    grpc_gcp_handshaker_req* req, grpc_gcp_handshake_protocol key,
+    const char* service_account);
+
+/**
+ * This method sets the value for rpc_versions field of either ALTS
+ * client_start or server_start handshake request.
+ *
+ * - req: an ALTS handshake request.
+ * - max_major: a major version of maximum supported RPC version.
+ * - max_minor: a minor version of maximum supported RPC version.
+ * - min_major: a major version of minimum supported RPC version.
+ * - min_minor: a minor version of minimum supported RPC version.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_set_rpc_versions(grpc_gcp_handshaker_req* req,
+                                              uint32_t max_major,
+                                              uint32_t max_minor,
+                                              uint32_t min_major,
+                                              uint32_t min_minor);
+
+/**
+ * This method serializes an ALTS handshake request and returns a data stream.
+ *
+ * - req: an ALTS handshake request.
+ * - slice: a data stream where the serialized result will be written.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_req_encode(grpc_gcp_handshaker_req* req,
+                                    grpc_slice* slice);
+
+/* This method destroys an ALTS handshake request. */
+void grpc_gcp_handshaker_req_destroy(grpc_gcp_handshaker_req* req);
+
+/* This method creates an ALTS handshake response. */
+grpc_gcp_handshaker_resp* grpc_gcp_handshaker_resp_create(void);
+
+/**
+ * This method de-serializes a data stream and stores the result
+ * in an ALTS handshake response.
+ *
+ * - slice: a data stream containing a serialized ALTS handshake response.
+ * - resp: an ALTS handshake response used to hold de-serialized result.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_handshaker_resp_decode(grpc_slice slice,
+                                     grpc_gcp_handshaker_resp* resp);
+
+/* This method destroys an ALTS handshake response. */
+void grpc_gcp_handshaker_resp_destroy(grpc_gcp_handshaker_resp* resp);
+
+#endif /* GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_SERVICE_API_H */
diff --git a/src/core/tsi/alts/handshaker/alts_handshaker_service_api_util.cc b/src/core/tsi/alts/handshaker/alts_handshaker_service_api_util.cc
new file mode 100644
index 0000000000..e0e4184686
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_handshaker_service_api_util.cc
@@ -0,0 +1,143 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/alts_handshaker_service_api_util.h"
+
+void add_repeated_field(repeated_field** head, const void* data) {
+  repeated_field* field =
+      static_cast<repeated_field*>(gpr_zalloc(sizeof(*field)));
+  field->data = data;
+  if (*head == nullptr) {
+    *head = field;
+    (*head)->next = nullptr;
+  } else {
+    field->next = *head;
+    *head = field;
+  }
+}
+
+void destroy_repeated_field_list_identity(repeated_field* head) {
+  repeated_field* field = head;
+  while (field != nullptr) {
+    repeated_field* next_field = field->next;
+    const grpc_gcp_identity* identity =
+        static_cast<const grpc_gcp_identity*>(field->data);
+    destroy_slice(static_cast<grpc_slice*>(identity->hostname.arg));
+    destroy_slice(static_cast<grpc_slice*>(identity->service_account.arg));
+    gpr_free((void*)identity);
+    gpr_free(field);
+    field = next_field;
+  }
+}
+
+void destroy_repeated_field_list_string(repeated_field* head) {
+  repeated_field* field = head;
+  while (field != nullptr) {
+    repeated_field* next_field = field->next;
+    destroy_slice((grpc_slice*)field->data);
+    gpr_free(field);
+    field = next_field;
+  }
+}
+
+grpc_slice* create_slice(const char* data, size_t size) {
+  grpc_slice slice = grpc_slice_from_copied_buffer(data, size);
+  grpc_slice* cb_slice =
+      static_cast<grpc_slice*>(gpr_zalloc(sizeof(*cb_slice)));
+  memcpy(cb_slice, &slice, sizeof(*cb_slice));
+  return cb_slice;
+}
+
+void destroy_slice(grpc_slice* slice) {
+  if (slice != nullptr) {
+    grpc_slice_unref(*slice);
+    gpr_free(slice);
+  }
+}
+
+bool encode_string_or_bytes_cb(pb_ostream_t* stream, const pb_field_t* field,
+                               void* const* arg) {
+  grpc_slice* slice = static_cast<grpc_slice*>(*arg);
+  if (!pb_encode_tag_for_field(stream, field)) return false;
+  return pb_encode_string(stream, GRPC_SLICE_START_PTR(*slice),
+                          GRPC_SLICE_LENGTH(*slice));
+}
+
+bool encode_repeated_identity_cb(pb_ostream_t* stream, const pb_field_t* field,
+                                 void* const* arg) {
+  repeated_field* var = static_cast<repeated_field*>(*arg);
+  while (var != nullptr) {
+    if (!pb_encode_tag_for_field(stream, field)) return false;
+    if (!pb_encode_submessage(stream, grpc_gcp_Identity_fields,
+                              (grpc_gcp_identity*)var->data))
+      return false;
+    var = var->next;
+  }
+  return true;
+}
+
+bool encode_repeated_string_cb(pb_ostream_t* stream, const pb_field_t* field,
+                               void* const* arg) {
+  repeated_field* var = static_cast<repeated_field*>(*arg);
+  while (var != nullptr) {
+    if (!pb_encode_tag_for_field(stream, field)) return false;
+    const grpc_slice* slice = static_cast<const grpc_slice*>(var->data);
+    if (!pb_encode_string(stream, GRPC_SLICE_START_PTR(*slice),
+                          GRPC_SLICE_LENGTH(*slice)))
+      return false;
+    var = var->next;
+  }
+  return true;
+}
+
+bool decode_string_or_bytes_cb(pb_istream_t* stream, const pb_field_t* field,
+                               void** arg) {
+  grpc_slice slice = grpc_slice_malloc(stream->bytes_left);
+  grpc_slice* cb_slice =
+      static_cast<grpc_slice*>(gpr_zalloc(sizeof(*cb_slice)));
+  memcpy(cb_slice, &slice, sizeof(*cb_slice));
+  if (!pb_read(stream, GRPC_SLICE_START_PTR(*cb_slice), stream->bytes_left))
+    return false;
+  *arg = cb_slice;
+  return true;
+}
+
+bool decode_repeated_identity_cb(pb_istream_t* stream, const pb_field_t* field,
+                                 void** arg) {
+  grpc_gcp_identity* identity =
+      static_cast<grpc_gcp_identity*>(gpr_zalloc(sizeof(*identity)));
+  identity->hostname.funcs.decode = decode_string_or_bytes_cb;
+  identity->service_account.funcs.decode = decode_string_or_bytes_cb;
+  add_repeated_field(reinterpret_cast<repeated_field**>(arg), identity);
+  if (!pb_decode(stream, grpc_gcp_Identity_fields, identity)) return false;
+  return true;
+}
+
+bool decode_repeated_string_cb(pb_istream_t* stream, const pb_field_t* field,
+                               void** arg) {
+  grpc_slice slice = grpc_slice_malloc(stream->bytes_left);
+  grpc_slice* cb_slice =
+      static_cast<grpc_slice*>(gpr_zalloc(sizeof(*cb_slice)));
+  memcpy(cb_slice, &slice, sizeof(grpc_slice));
+  if (!pb_read(stream, GRPC_SLICE_START_PTR(*cb_slice), stream->bytes_left))
+    return false;
+  add_repeated_field(reinterpret_cast<repeated_field**>(arg), cb_slice);
+  return true;
+}
diff --git a/src/core/tsi/alts/handshaker/alts_handshaker_service_api_util.h b/src/core/tsi/alts/handshaker/alts_handshaker_service_api_util.h
new file mode 100644
index 0000000000..8fe8f73f8b
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_handshaker_service_api_util.h
@@ -0,0 +1,149 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_SERVICE_API_UTIL_H
+#define GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_SERVICE_API_UTIL_H
+
+#include <grpc/support/port_platform.h>
+
+#include "third_party/nanopb/pb_decode.h"
+#include "third_party/nanopb/pb_encode.h"
+
+#include <grpc/slice.h>
+#include <grpc/slice_buffer.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/tsi/alts/handshaker/handshaker.pb.h"
+
+/**
+ * An implementation of utility functions used to serialize/
+ * de-serialize ALTS handshake requests/responses. All APIs in the header
+ * are thread-compatible.
+ */
+
+/* Renaming of message/field structs generated by nanopb compiler. */
+typedef grpc_gcp_HandshakeProtocol grpc_gcp_handshake_protocol;
+typedef grpc_gcp_NetworkProtocol grpc_gcp_network_protocol;
+typedef grpc_gcp_Identity grpc_gcp_identity;
+typedef grpc_gcp_NextHandshakeMessageReq grpc_gcp_next_handshake_message_req;
+typedef grpc_gcp_ServerHandshakeParameters grpc_gcp_server_handshake_parameters;
+typedef grpc_gcp_Endpoint grpc_gcp_endpoint;
+typedef grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry
+    grpc_gcp_handshake_parameters_entry;
+typedef grpc_gcp_StartClientHandshakeReq grpc_gcp_start_client_handshake_req;
+typedef grpc_gcp_StartServerHandshakeReq grpc_gcp_start_server_handshake_req;
+typedef grpc_gcp_HandshakerReq grpc_gcp_handshaker_req;
+typedef grpc_gcp_HandshakerResult grpc_gcp_handshaker_result;
+typedef grpc_gcp_HandshakerStatus grpc_gcp_handshaker_status;
+typedef grpc_gcp_HandshakerResp grpc_gcp_handshaker_resp;
+
+typedef enum {
+  CLIENT_START_REQ = 0, /* StartClientHandshakeReq. */
+  SERVER_START_REQ = 1, /* StartServerHandshakeReq. */
+  NEXT_REQ = 2,         /* NextHandshakeMessageReq. */
+} grpc_gcp_handshaker_req_type;
+
+/**
+ *  A struct representing a repeated field. The struct is used to organize all
+ *  instances of a specific repeated field into a linked list, which then will
+ *  be used at encode/decode phase. For instance at the encode phase, the encode
+ *  function will iterate through the list, encode each field, and then output
+ *  the result to the stream.
+ */
+typedef struct repeated_field_ {
+  struct repeated_field_* next;
+  const void* data;
+} repeated_field;
+
+/**
+ * This method adds a repeated field to the head of repeated field list.
+ *
+ * - head: a head of repeated field list.
+ * - field: a repeated field to be added to the list.
+ */
+void add_repeated_field(repeated_field** head, const void* field);
+
+/**
+ * This method destroys a repeated field list that consists of string type
+ * fields.
+ *
+ * - head: a head of repeated field list.
+ */
+void destroy_repeated_field_list_string(repeated_field* head);
+
+/**
+ * This method destroys a repeated field list that consists of
+ * grpc_gcp_identity type fields.
+ *
+ * - head: a head of repeated field list.
+ */
+void destroy_repeated_field_list_identity(repeated_field* head);
+
+/**
+ * This method creates a grpc_slice instance by copying a data buffer. It is
+ * similar to grpc_slice_from_copied_buffer() except that it returns an instance
+ * allocated from the heap.
+ *
+ * - data: a data buffer to be copied to grpc_slice instance.
+ * - size: size of data buffer.
+ */
+grpc_slice* create_slice(const char* data, size_t size);
+
+/* This method destroys a grpc_slice instance. */
+void destroy_slice(grpc_slice* slice);
+
+/**
+ * The following encode/decode functions will be assigned to encode/decode
+ * function pointers of pb_callback_t struct (defined in
+ * //third_party/nanopb/pb.h), that represent a repeated field with a dynamic
+ * length (e.g., a string type or repeated field).
+ */
+
+/* This method is an encode callback function for a string or byte array. */
+bool encode_string_or_bytes_cb(pb_ostream_t* stream, const pb_field_t* field,
+                               void* const* arg);
+
+/**
+ * This method is an encode callback function for a repeated grpc_gcp_identity
+ * field.
+ */
+bool encode_repeated_identity_cb(pb_ostream_t* stream, const pb_field_t* field,
+                                 void* const* arg);
+
+/* This method is an encode callback function for a repeated string field. */
+bool encode_repeated_string_cb(pb_ostream_t* stream, const pb_field_t* field,
+                               void* const* arg);
+
+/**
+ * This method is a decode callback function for a string or byte array field.
+ */
+bool decode_string_or_bytes_cb(pb_istream_t* stream, const pb_field_t* field,
+                               void** arg);
+/**
+ * This method is a decode callback function for a repeated grpc_gcp_identity
+ * field.
+ */
+bool decode_repeated_identity_cb(pb_istream_t* stream, const pb_field_t* field,
+                                 void** arg);
+
+/* This method is a decode callback function for a repeated string field. */
+bool decode_repeated_string_cb(pb_istream_t* stream, const pb_field_t* field,
+                               void** arg);
+
+#endif /* GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_HANDSHAKER_SERVICE_API_UTIL_H */
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_event.cc b/src/core/tsi/alts/handshaker/alts_tsi_event.cc
new file mode 100644
index 0000000000..ec0bf12b95
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_tsi_event.cc
@@ -0,0 +1,73 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/alts_tsi_event.h"
+
+#include <grpc/grpc.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+tsi_result alts_tsi_event_create(alts_tsi_handshaker* handshaker,
+                                 tsi_handshaker_on_next_done_cb cb,
+                                 void* user_data,
+                                 grpc_alts_credentials_options* options,
+                                 grpc_slice target_name,
+                                 alts_tsi_event** event) {
+  if (event == nullptr || handshaker == nullptr || cb == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid arguments to alts_tsi_event_create()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_tsi_event* e = static_cast<alts_tsi_event*>(gpr_zalloc(sizeof(*e)));
+  e->handshaker = handshaker;
+  e->cb = cb;
+  e->user_data = user_data;
+  e->options = grpc_alts_credentials_options_copy(options);
+  e->target_name = grpc_slice_copy(target_name);
+  grpc_metadata_array_init(&e->initial_metadata);
+  grpc_metadata_array_init(&e->trailing_metadata);
+  *event = e;
+  return TSI_OK;
+}
+
+void alts_tsi_event_dispatch_to_handshaker(alts_tsi_event* event, bool is_ok) {
+  if (event == nullptr) {
+    gpr_log(
+        GPR_ERROR,
+        "ALTS TSI event is nullptr in alts_tsi_event_dispatch_to_handshaker()");
+    return;
+  }
+  alts_tsi_handshaker_handle_response(event->handshaker, event->recv_buffer,
+                                      event->status, &event->details, event->cb,
+                                      event->user_data, is_ok);
+}
+
+void alts_tsi_event_destroy(alts_tsi_event* event) {
+  if (event == nullptr) {
+    return;
+  }
+  grpc_byte_buffer_destroy(event->send_buffer);
+  grpc_byte_buffer_destroy(event->recv_buffer);
+  grpc_metadata_array_destroy(&event->initial_metadata);
+  grpc_metadata_array_destroy(&event->trailing_metadata);
+  grpc_slice_unref(event->details);
+  grpc_slice_unref(event->target_name);
+  grpc_alts_credentials_options_destroy(event->options);
+  gpr_free(event);
+}
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_event.h b/src/core/tsi/alts/handshaker/alts_tsi_event.h
new file mode 100644
index 0000000000..043e75d4a9
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_tsi_event.h
@@ -0,0 +1,93 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_EVENT_H
+#define GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_EVENT_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/byte_buffer.h>
+#include <grpc/byte_buffer_reader.h>
+
+#include "src/core/tsi/alts/handshaker/alts_tsi_handshaker.h"
+#include "src/core/tsi/transport_security_interface.h"
+
+/**
+ * A ALTS TSI event interface. In asynchronous implementation of
+ * tsi_handshaker_next(), the function will exit after scheduling a handshaker
+ * request to ALTS handshaker service without waiting for response to return.
+ * The event is used to link the scheduled handshaker request with the
+ * corresponding response so that enough context information can be inferred
+ * from it to handle the response. All APIs in the header are thread-compatible.
+ */
+
+/**
+ * Main struct for ALTS TSI event. It retains ownership on send_buffer and
+ * recv_buffer, but not on handshaker.
+ */
+typedef struct alts_tsi_event {
+  alts_tsi_handshaker* handshaker;
+  grpc_byte_buffer* send_buffer;
+  grpc_byte_buffer* recv_buffer;
+  grpc_status_code status;
+  grpc_slice details;
+  grpc_metadata_array initial_metadata;
+  grpc_metadata_array trailing_metadata;
+  tsi_handshaker_on_next_done_cb cb;
+  void* user_data;
+  grpc_alts_credentials_options* options;
+  grpc_slice target_name;
+} alts_tsi_event;
+
+/**
+ * This method creates a ALTS TSI event.
+ *
+ * - handshaker: ALTS TSI handshaker instance associated with the event to be
+ *   created. The created event does not own the handshaker instance.
+ * - cb: callback function to be called when handling data received from ALTS
+ *   handshaker service.
+ * - user_data: argument to callback function.
+ * - options: ALTS credentials options.
+ * - target_name: name of endpoint used for secure naming check.
+ * - event: address of ALTS TSI event instance to be returned from the method.
+ *
+ * It returns TSI_OK on success and an error status code on failure.
+ */
+tsi_result alts_tsi_event_create(alts_tsi_handshaker* handshaker,
+                                 tsi_handshaker_on_next_done_cb cb,
+                                 void* user_data,
+                                 grpc_alts_credentials_options* options,
+                                 grpc_slice target_name,
+                                 alts_tsi_event** event);
+
+/**
+ * This method dispatches a ALTS TSI event received from the handshaker service,
+ * and a boolean flag indicating if the event is valid to read to ALTS TSI
+ * handshaker to process. It is called by TSI thread.
+ *
+ * - event: ALTS TSI event instance.
+ * - is_ok: a boolean value indicating if the event is valid to read.
+ */
+void alts_tsi_event_dispatch_to_handshaker(alts_tsi_event* event, bool is_ok);
+
+/**
+ * This method destroys the ALTS TSI event.
+ */
+void alts_tsi_event_destroy(alts_tsi_event* event);
+
+#endif /* GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_EVENT_H */
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_handshaker.cc b/src/core/tsi/alts/handshaker/alts_tsi_handshaker.cc
new file mode 100644
index 0000000000..529f2103c7
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_tsi_handshaker.cc
@@ -0,0 +1,483 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/alts_tsi_handshaker.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/thd_id.h>
+
+#include "src/core/lib/gpr/host_port.h"
+#include "src/core/lib/gprpp/thd.h"
+#include "src/core/tsi/alts/frame_protector/alts_frame_protector.h"
+#include "src/core/tsi/alts/handshaker/alts_handshaker_client.h"
+#include "src/core/tsi/alts/handshaker/alts_tsi_utils.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_zero_copy_grpc_protector.h"
+#include "src/core/tsi/alts_transport_security.h"
+
+#define TSI_ALTS_INITIAL_BUFFER_SIZE 256
+
+static alts_shared_resource* kSharedResource = alts_get_shared_resource();
+
+/* Main struct for ALTS TSI handshaker. */
+typedef struct alts_tsi_handshaker {
+  tsi_handshaker base;
+  alts_handshaker_client* client;
+  grpc_slice recv_bytes;
+  grpc_slice target_name;
+  unsigned char* buffer;
+  size_t buffer_size;
+  bool is_client;
+  bool has_sent_start_message;
+  grpc_alts_credentials_options* options;
+} alts_tsi_handshaker;
+
+/* Main struct for ALTS TSI handshaker result. */
+typedef struct alts_tsi_handshaker_result {
+  tsi_handshaker_result base;
+  char* peer_identity;
+  char* key_data;
+  unsigned char* unused_bytes;
+  size_t unused_bytes_size;
+  grpc_slice rpc_versions;
+  bool is_client;
+} alts_tsi_handshaker_result;
+
+static tsi_result handshaker_result_extract_peer(
+    const tsi_handshaker_result* self, tsi_peer* peer) {
+  if (self == nullptr || peer == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid argument to handshaker_result_extract_peer()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_tsi_handshaker_result* result =
+      reinterpret_cast<alts_tsi_handshaker_result*>(
+          const_cast<tsi_handshaker_result*>(self));
+  GPR_ASSERT(kTsiAltsNumOfPeerProperties == 3);
+  tsi_result ok = tsi_construct_peer(kTsiAltsNumOfPeerProperties, peer);
+  int index = 0;
+  if (ok != TSI_OK) {
+    gpr_log(GPR_ERROR, "Failed to construct tsi peer");
+    return ok;
+  }
+  GPR_ASSERT(&peer->properties[index] != nullptr);
+  ok = tsi_construct_string_peer_property_from_cstring(
+      TSI_CERTIFICATE_TYPE_PEER_PROPERTY, TSI_ALTS_CERTIFICATE_TYPE,
+      &peer->properties[index]);
+  if (ok != TSI_OK) {
+    tsi_peer_destruct(peer);
+    gpr_log(GPR_ERROR, "Failed to set tsi peer property");
+    return ok;
+  }
+  index++;
+  GPR_ASSERT(&peer->properties[index] != nullptr);
+  ok = tsi_construct_string_peer_property_from_cstring(
+      TSI_ALTS_SERVICE_ACCOUNT_PEER_PROPERTY, result->peer_identity,
+      &peer->properties[index]);
+  if (ok != TSI_OK) {
+    tsi_peer_destruct(peer);
+    gpr_log(GPR_ERROR, "Failed to set tsi peer property");
+  }
+  index++;
+  GPR_ASSERT(&peer->properties[index] != nullptr);
+  ok = tsi_construct_string_peer_property(
+      TSI_ALTS_RPC_VERSIONS,
+      reinterpret_cast<char*>(GRPC_SLICE_START_PTR(result->rpc_versions)),
+      GRPC_SLICE_LENGTH(result->rpc_versions), &peer->properties[2]);
+  if (ok != TSI_OK) {
+    tsi_peer_destruct(peer);
+    gpr_log(GPR_ERROR, "Failed to set tsi peer property");
+  }
+  GPR_ASSERT(++index == kTsiAltsNumOfPeerProperties);
+  return ok;
+}
+
+static tsi_result handshaker_result_create_zero_copy_grpc_protector(
+    const tsi_handshaker_result* self, size_t* max_output_protected_frame_size,
+    tsi_zero_copy_grpc_protector** protector) {
+  if (self == nullptr || protector == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to create_zero_copy_grpc_protector()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_tsi_handshaker_result* result =
+      reinterpret_cast<alts_tsi_handshaker_result*>(
+          const_cast<tsi_handshaker_result*>(self));
+  tsi_result ok = alts_zero_copy_grpc_protector_create(
+      reinterpret_cast<const uint8_t*>(result->key_data),
+      kAltsAes128GcmRekeyKeyLength, /*is_rekey=*/true, result->is_client,
+      /*is_integrity_only=*/false, max_output_protected_frame_size, protector);
+  if (ok != TSI_OK) {
+    gpr_log(GPR_ERROR, "Failed to create zero-copy grpc protector");
+  }
+  return ok;
+}
+
+static tsi_result handshaker_result_create_frame_protector(
+    const tsi_handshaker_result* self, size_t* max_output_protected_frame_size,
+    tsi_frame_protector** protector) {
+  if (self == nullptr || protector == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to handshaker_result_create_frame_protector()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_tsi_handshaker_result* result =
+      reinterpret_cast<alts_tsi_handshaker_result*>(
+          const_cast<tsi_handshaker_result*>(self));
+  tsi_result ok = alts_create_frame_protector(
+      reinterpret_cast<const uint8_t*>(result->key_data),
+      kAltsAes128GcmRekeyKeyLength, result->is_client, /*is_rekey=*/true,
+      max_output_protected_frame_size, protector);
+  if (ok != TSI_OK) {
+    gpr_log(GPR_ERROR, "Failed to create frame protector");
+  }
+  return ok;
+}
+
+static tsi_result handshaker_result_get_unused_bytes(
+    const tsi_handshaker_result* self, const unsigned char** bytes,
+    size_t* bytes_size) {
+  if (self == nullptr || bytes == nullptr || bytes_size == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to handshaker_result_get_unused_bytes()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_tsi_handshaker_result* result =
+      reinterpret_cast<alts_tsi_handshaker_result*>(
+          const_cast<tsi_handshaker_result*>(self));
+  *bytes = result->unused_bytes;
+  *bytes_size = result->unused_bytes_size;
+  return TSI_OK;
+}
+
+static void handshaker_result_destroy(tsi_handshaker_result* self) {
+  if (self == nullptr) {
+    return;
+  }
+  alts_tsi_handshaker_result* result =
+      reinterpret_cast<alts_tsi_handshaker_result*>(
+          const_cast<tsi_handshaker_result*>(self));
+  gpr_free(result->peer_identity);
+  gpr_free(result->key_data);
+  gpr_free(result->unused_bytes);
+  grpc_slice_unref(result->rpc_versions);
+  gpr_free(result);
+}
+
+static const tsi_handshaker_result_vtable result_vtable = {
+    handshaker_result_extract_peer,
+    handshaker_result_create_zero_copy_grpc_protector,
+    handshaker_result_create_frame_protector,
+    handshaker_result_get_unused_bytes, handshaker_result_destroy};
+
+static tsi_result create_handshaker_result(grpc_gcp_handshaker_resp* resp,
+                                           bool is_client,
+                                           tsi_handshaker_result** self) {
+  if (self == nullptr || resp == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid arguments to create_handshaker_result()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  grpc_slice* key = static_cast<grpc_slice*>(resp->result.key_data.arg);
+  GPR_ASSERT(key != nullptr);
+  grpc_slice* identity =
+      static_cast<grpc_slice*>(resp->result.peer_identity.service_account.arg);
+  if (identity == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid service account");
+    return TSI_FAILED_PRECONDITION;
+  }
+  if (GRPC_SLICE_LENGTH(*key) < kAltsAes128GcmRekeyKeyLength) {
+    gpr_log(GPR_ERROR, "Bad key length");
+    return TSI_FAILED_PRECONDITION;
+  }
+  alts_tsi_handshaker_result* result =
+      static_cast<alts_tsi_handshaker_result*>(gpr_zalloc(sizeof(*result)));
+  result->key_data =
+      static_cast<char*>(gpr_zalloc(kAltsAes128GcmRekeyKeyLength));
+  memcpy(result->key_data, GRPC_SLICE_START_PTR(*key),
+         kAltsAes128GcmRekeyKeyLength);
+  result->peer_identity = grpc_slice_to_c_string(*identity);
+  if (!resp->result.has_peer_rpc_versions) {
+    gpr_log(GPR_ERROR, "Peer does not set RPC protocol versions.");
+    return TSI_FAILED_PRECONDITION;
+  }
+  if (!grpc_gcp_rpc_protocol_versions_encode(&resp->result.peer_rpc_versions,
+                                             &result->rpc_versions)) {
+    gpr_log(GPR_ERROR, "Failed to serialize peer's RPC protocol versions.");
+    return TSI_FAILED_PRECONDITION;
+  }
+  result->is_client = is_client;
+  result->base.vtable = &result_vtable;
+  *self = &result->base;
+  return TSI_OK;
+}
+
+static tsi_result handshaker_next(
+    tsi_handshaker* self, const unsigned char* received_bytes,
+    size_t received_bytes_size, const unsigned char** bytes_to_send,
+    size_t* bytes_to_send_size, tsi_handshaker_result** result,
+    tsi_handshaker_on_next_done_cb cb, void* user_data) {
+  if (self == nullptr || cb == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid arguments to handshaker_next()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_tsi_handshaker* handshaker =
+      reinterpret_cast<alts_tsi_handshaker*>(self);
+  tsi_result ok = TSI_OK;
+  alts_tsi_event* event = nullptr;
+  ok = alts_tsi_event_create(handshaker, cb, user_data, handshaker->options,
+                             handshaker->target_name, &event);
+  if (ok != TSI_OK) {
+    gpr_log(GPR_ERROR, "Failed to create ALTS TSI event");
+    return ok;
+  }
+  grpc_slice slice = (received_bytes == nullptr || received_bytes_size == 0)
+                         ? grpc_empty_slice()
+                         : grpc_slice_from_copied_buffer(
+                               reinterpret_cast<const char*>(received_bytes),
+                               received_bytes_size);
+  if (!handshaker->has_sent_start_message) {
+    ok = handshaker->is_client
+             ? alts_handshaker_client_start_client(handshaker->client, event)
+             : alts_handshaker_client_start_server(handshaker->client, event,
+                                                   &slice);
+    handshaker->has_sent_start_message = true;
+  } else {
+    if (!GRPC_SLICE_IS_EMPTY(handshaker->recv_bytes)) {
+      grpc_slice_unref(handshaker->recv_bytes);
+    }
+    handshaker->recv_bytes = grpc_slice_ref(slice);
+    ok = alts_handshaker_client_next(handshaker->client, event, &slice);
+  }
+  grpc_slice_unref(slice);
+  if (ok != TSI_OK) {
+    gpr_log(GPR_ERROR, "Failed to schedule ALTS handshaker requests");
+    return ok;
+  }
+  return TSI_ASYNC;
+}
+
+static void handshaker_destroy(tsi_handshaker* self) {
+  if (self == nullptr) {
+    return;
+  }
+  alts_tsi_handshaker* handshaker =
+      reinterpret_cast<alts_tsi_handshaker*>(self);
+  alts_handshaker_client_destroy(handshaker->client);
+  grpc_slice_unref(handshaker->recv_bytes);
+  grpc_slice_unref(handshaker->target_name);
+  grpc_alts_credentials_options_destroy(handshaker->options);
+  gpr_free(handshaker->buffer);
+  gpr_free(handshaker);
+}
+
+static const tsi_handshaker_vtable handshaker_vtable = {
+    nullptr,        nullptr, nullptr, nullptr, nullptr, handshaker_destroy,
+    handshaker_next};
+
+static void thread_worker(void* arg) {
+  while (true) {
+    grpc_event event = grpc_completion_queue_next(
+        kSharedResource->cq, gpr_inf_future(GPR_CLOCK_REALTIME), nullptr);
+    GPR_ASSERT(event.type != GRPC_QUEUE_TIMEOUT);
+    if (event.type == GRPC_QUEUE_SHUTDOWN) {
+      /* signal alts_tsi_shutdown() to destroy completion queue. */
+      grpc_tsi_alts_signal_for_cq_destroy();
+      break;
+    }
+    /* event.type == GRPC_OP_COMPLETE. */
+    alts_tsi_event* alts_event = static_cast<alts_tsi_event*>(event.tag);
+    alts_tsi_event_dispatch_to_handshaker(alts_event, event.success);
+    alts_tsi_event_destroy(alts_event);
+  }
+}
+
+static void init_shared_resources(const char* handshaker_service_url) {
+  GPR_ASSERT(handshaker_service_url != nullptr);
+  gpr_mu_lock(&kSharedResource->mu);
+  if (kSharedResource->channel == nullptr) {
+    gpr_cv_init(&kSharedResource->cv);
+    kSharedResource->channel =
+        grpc_insecure_channel_create(handshaker_service_url, nullptr, nullptr);
+    kSharedResource->cq = grpc_completion_queue_create_for_next(nullptr);
+    kSharedResource->thread =
+        grpc_core::Thread("alts_tsi_handshaker", &thread_worker, nullptr);
+    kSharedResource->thread.Start();
+  }
+  gpr_mu_unlock(&kSharedResource->mu);
+}
+
+tsi_result alts_tsi_handshaker_create(
+    const grpc_alts_credentials_options* options, const char* target_name,
+    const char* handshaker_service_url, bool is_client, tsi_handshaker** self) {
+  if (handshaker_service_url == nullptr || self == nullptr ||
+      options == nullptr || (is_client && target_name == nullptr)) {
+    gpr_log(GPR_ERROR, "Invalid arguments to alts_tsi_handshaker_create()");
+    return TSI_INVALID_ARGUMENT;
+  }
+  init_shared_resources(handshaker_service_url);
+  alts_handshaker_client* client = alts_grpc_handshaker_client_create(
+      kSharedResource->channel, kSharedResource->cq, handshaker_service_url);
+  if (client == nullptr) {
+    gpr_log(GPR_ERROR, "Failed to create ALTS handshaker client");
+    return TSI_FAILED_PRECONDITION;
+  }
+  alts_tsi_handshaker* handshaker =
+      static_cast<alts_tsi_handshaker*>(gpr_zalloc(sizeof(*handshaker)));
+  handshaker->client = client;
+  handshaker->buffer_size = TSI_ALTS_INITIAL_BUFFER_SIZE;
+  handshaker->buffer =
+      static_cast<unsigned char*>(gpr_zalloc(handshaker->buffer_size));
+  handshaker->is_client = is_client;
+  handshaker->has_sent_start_message = false;
+  handshaker->target_name = target_name == nullptr
+                                ? grpc_empty_slice()
+                                : grpc_slice_from_static_string(target_name);
+  handshaker->options = grpc_alts_credentials_options_copy(options);
+  handshaker->base.vtable = &handshaker_vtable;
+  *self = &handshaker->base;
+  return TSI_OK;
+}
+
+static bool is_handshake_finished_properly(grpc_gcp_handshaker_resp* resp) {
+  GPR_ASSERT(resp != nullptr);
+  if (resp->has_result) {
+    return true;
+  }
+  return false;
+}
+
+static void set_unused_bytes(tsi_handshaker_result* self,
+                             grpc_slice* recv_bytes, size_t bytes_consumed) {
+  GPR_ASSERT(recv_bytes != nullptr && self != nullptr);
+  if (GRPC_SLICE_LENGTH(*recv_bytes) == bytes_consumed) {
+    return;
+  }
+  alts_tsi_handshaker_result* result =
+      reinterpret_cast<alts_tsi_handshaker_result*>(self);
+  result->unused_bytes_size = GRPC_SLICE_LENGTH(*recv_bytes) - bytes_consumed;
+  result->unused_bytes =
+      static_cast<unsigned char*>(gpr_zalloc(result->unused_bytes_size));
+  memcpy(result->unused_bytes,
+         GRPC_SLICE_START_PTR(*recv_bytes) + bytes_consumed,
+         result->unused_bytes_size);
+}
+
+void alts_tsi_handshaker_handle_response(alts_tsi_handshaker* handshaker,
+                                         grpc_byte_buffer* recv_buffer,
+                                         grpc_status_code status,
+                                         grpc_slice* details,
+                                         tsi_handshaker_on_next_done_cb cb,
+                                         void* user_data, bool is_ok) {
+  /* Invalid input check. */
+  if (cb == nullptr) {
+    gpr_log(GPR_ERROR,
+            "cb is nullptr in alts_tsi_handshaker_handle_response()");
+    return;
+  }
+  if (handshaker == nullptr || recv_buffer == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to alts_tsi_handshaker_handle_response()");
+    cb(TSI_INTERNAL_ERROR, user_data, nullptr, 0, nullptr);
+    return;
+  }
+  /* Failed grpc call check. */
+  if (!is_ok || status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "grpc call made to handshaker service failed");
+    if (details != nullptr) {
+      char* error_details = grpc_slice_to_c_string(*details);
+      gpr_log(GPR_ERROR, "error details:%s", error_details);
+      gpr_free(error_details);
+    }
+    cb(TSI_INTERNAL_ERROR, user_data, nullptr, 0, nullptr);
+    return;
+  }
+  grpc_gcp_handshaker_resp* resp =
+      alts_tsi_utils_deserialize_response(recv_buffer);
+  /* Invalid handshaker response check. */
+  if (resp == nullptr) {
+    gpr_log(GPR_ERROR, "alts_tsi_utils_deserialize_response() failed");
+    cb(TSI_DATA_CORRUPTED, user_data, nullptr, 0, nullptr);
+    return;
+  }
+  grpc_slice* slice = static_cast<grpc_slice*>(resp->out_frames.arg);
+  unsigned char* bytes_to_send = nullptr;
+  size_t bytes_to_send_size = 0;
+  if (slice != nullptr) {
+    bytes_to_send_size = GRPC_SLICE_LENGTH(*slice);
+    while (bytes_to_send_size > handshaker->buffer_size) {
+      handshaker->buffer_size *= 2;
+      handshaker->buffer = static_cast<unsigned char*>(
+          gpr_realloc(handshaker->buffer, handshaker->buffer_size));
+    }
+    memcpy(handshaker->buffer, GRPC_SLICE_START_PTR(*slice),
+           bytes_to_send_size);
+    bytes_to_send = handshaker->buffer;
+  }
+  tsi_handshaker_result* result = nullptr;
+  if (is_handshake_finished_properly(resp)) {
+    create_handshaker_result(resp, handshaker->is_client, &result);
+    set_unused_bytes(result, &handshaker->recv_bytes, resp->bytes_consumed);
+  }
+  grpc_status_code code = static_cast<grpc_status_code>(resp->status.code);
+  grpc_gcp_handshaker_resp_destroy(resp);
+  cb(alts_tsi_utils_convert_to_tsi_result(code), user_data, bytes_to_send,
+     bytes_to_send_size, result);
+}
+
+namespace grpc_core {
+namespace internal {
+
+bool alts_tsi_handshaker_get_has_sent_start_message_for_testing(
+    alts_tsi_handshaker* handshaker) {
+  GPR_ASSERT(handshaker != nullptr);
+  return handshaker->has_sent_start_message;
+}
+
+bool alts_tsi_handshaker_get_is_client_for_testing(
+    alts_tsi_handshaker* handshaker) {
+  GPR_ASSERT(handshaker != nullptr);
+  return handshaker->is_client;
+}
+
+void alts_tsi_handshaker_set_recv_bytes_for_testing(
+    alts_tsi_handshaker* handshaker, grpc_slice* slice) {
+  GPR_ASSERT(handshaker != nullptr && slice != nullptr);
+  handshaker->recv_bytes = grpc_slice_ref(*slice);
+}
+
+grpc_slice alts_tsi_handshaker_get_recv_bytes_for_testing(
+    alts_tsi_handshaker* handshaker) {
+  GPR_ASSERT(handshaker != nullptr);
+  return handshaker->recv_bytes;
+}
+
+void alts_tsi_handshaker_set_client_for_testing(
+    alts_tsi_handshaker* handshaker, alts_handshaker_client* client) {
+  GPR_ASSERT(handshaker != nullptr && client != nullptr);
+  alts_handshaker_client_destroy(handshaker->client);
+  handshaker->client = client;
+}
+
+}  // namespace internal
+}  // namespace grpc_core
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_handshaker.h b/src/core/tsi/alts/handshaker/alts_tsi_handshaker.h
new file mode 100644
index 0000000000..227b30ce53
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_tsi_handshaker.h
@@ -0,0 +1,83 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_HANDSHAKER_H
+#define GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_HANDSHAKER_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/grpc.h>
+
+#include "src/core/lib/security/credentials/alts/grpc_alts_credentials_options.h"
+#include "src/core/tsi/alts_transport_security.h"
+#include "src/core/tsi/transport_security.h"
+#include "src/core/tsi/transport_security_interface.h"
+
+#define TSI_ALTS_SERVICE_ACCOUNT_PEER_PROPERTY "service_accont"
+#define TSI_ALTS_CERTIFICATE_TYPE "ALTS"
+#define TSI_ALTS_RPC_VERSIONS "rpc_versions"
+
+const size_t kTsiAltsNumOfPeerProperties = 3;
+
+/**
+ * Main struct for ALTS TSI handshaker. All APIs in the header are
+ * thread-comptabile.
+ */
+typedef struct alts_tsi_handshaker alts_tsi_handshaker;
+
+/**
+ * This method creates a ALTS TSI handshaker instance.
+ *
+ * - options: ALTS credentials options containing information passed from TSI
+ *   caller (e.g., rpc protocol versions).
+ * - target_name: the name of the endpoint that the channel is connecting to,
+ *   and will be used for secure naming check.
+ * - handshaker_service_url: address of ALTS handshaker service in the format of
+ *   "host:port".
+ * - is_client: boolean value indicating if the handshaker is used at the client
+ *   (is_client = true) or server (is_client = false) side.
+ * - self: address of ALTS TSI handshaker instance to be returned from the
+ *   method.
+ *
+ * It returns TSI_OK on success and an error status code on failure.
+ */
+tsi_result alts_tsi_handshaker_create(
+    const grpc_alts_credentials_options* options, const char* target_name,
+    const char* handshaker_service_url, bool is_client, tsi_handshaker** self);
+
+/**
+ * This method handles handshaker response returned from ALTS handshaker
+ * service.
+ *
+ * - handshaker: ALTS TSI handshaker instance.
+ * - recv_buffer: buffer holding data received from the handshaker service.
+ * - status: status of the grpc call made to the handshaker service.
+ * - details: error details of the grpc call made to the handshaker service.
+ * - cb: callback function of ALTS TSI event.
+ * - user_data: argument of callback function.
+ * - is_ok: a boolean value indicating if the handshaker response is ok to read.
+ *
+ */
+void alts_tsi_handshaker_handle_response(alts_tsi_handshaker* handshaker,
+                                         grpc_byte_buffer* recv_buffer,
+                                         grpc_status_code status,
+                                         grpc_slice* details,
+                                         tsi_handshaker_on_next_done_cb cb,
+                                         void* user_data, bool is_ok);
+
+#endif /* GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_HANDSHAKER_H */
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_handshaker_private.h b/src/core/tsi/alts/handshaker/alts_tsi_handshaker_private.h
new file mode 100644
index 0000000000..9b7b9bb6b1
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_tsi_handshaker_private.h
@@ -0,0 +1,52 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_HANDSHAKER_PRIVATE_H
+#define GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_HANDSHAKER_PRIVATE_H
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/alts_handshaker_client.h"
+
+namespace grpc_core {
+namespace internal {
+
+/**
+ * Unsafe, use for testing only. It allows the caller to change the way the
+ * ALTS TSI handshaker schedules handshaker requests.
+ */
+void alts_tsi_handshaker_set_client_for_testing(alts_tsi_handshaker* handshaker,
+                                                alts_handshaker_client* client);
+
+/* For testing only. */
+bool alts_tsi_handshaker_get_has_sent_start_message_for_testing(
+    alts_tsi_handshaker* handshaker);
+
+bool alts_tsi_handshaker_get_is_client_for_testing(
+    alts_tsi_handshaker* handshaker);
+
+void alts_tsi_handshaker_set_recv_bytes_for_testing(
+    alts_tsi_handshaker* handshaker, grpc_slice* slice);
+
+grpc_slice alts_tsi_handshaker_get_recv_bytes_for_testing(
+    alts_tsi_handshaker* handshaker);
+
+}  // namespace internal
+}  // namespace grpc_core
+
+#endif /* GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_HANDSHAKER_PRIVATE_H */
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_utils.cc b/src/core/tsi/alts/handshaker/alts_tsi_utils.cc
new file mode 100644
index 0000000000..d9b5e6c945
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_tsi_utils.cc
@@ -0,0 +1,58 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/alts_tsi_utils.h"
+
+#include <grpc/byte_buffer_reader.h>
+
+tsi_result alts_tsi_utils_convert_to_tsi_result(grpc_status_code code) {
+  switch (code) {
+    case GRPC_STATUS_OK:
+      return TSI_OK;
+    case GRPC_STATUS_UNKNOWN:
+      return TSI_UNKNOWN_ERROR;
+    case GRPC_STATUS_INVALID_ARGUMENT:
+      return TSI_INVALID_ARGUMENT;
+    case GRPC_STATUS_NOT_FOUND:
+      return TSI_NOT_FOUND;
+    case GRPC_STATUS_INTERNAL:
+      return TSI_INTERNAL_ERROR;
+    default:
+      return TSI_UNKNOWN_ERROR;
+  }
+}
+
+grpc_gcp_handshaker_resp* alts_tsi_utils_deserialize_response(
+    grpc_byte_buffer* resp_buffer) {
+  GPR_ASSERT(resp_buffer != nullptr);
+  grpc_byte_buffer_reader bbr;
+  grpc_byte_buffer_reader_init(&bbr, resp_buffer);
+  grpc_slice slice = grpc_byte_buffer_reader_readall(&bbr);
+  grpc_gcp_handshaker_resp* resp = grpc_gcp_handshaker_resp_create();
+  bool ok = grpc_gcp_handshaker_resp_decode(slice, resp);
+  grpc_slice_unref(slice);
+  grpc_byte_buffer_reader_destroy(&bbr);
+  if (!ok) {
+    grpc_gcp_handshaker_resp_destroy(resp);
+    gpr_log(GPR_ERROR, "grpc_gcp_handshaker_resp_decode() failed");
+    return nullptr;
+  }
+  return resp;
+}
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_utils.h b/src/core/tsi/alts/handshaker/alts_tsi_utils.h
new file mode 100644
index 0000000000..9ef649de2b
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/alts_tsi_utils.h
@@ -0,0 +1,52 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_UTILS_H
+#define GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_UTILS_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/byte_buffer.h>
+#include <grpc/grpc.h>
+
+#include "src/core/tsi/alts/handshaker/alts_handshaker_service_api.h"
+#include "src/core/tsi/transport_security_interface.h"
+
+/**
+ * This method converts grpc_status_code code to the corresponding tsi_result
+ * code.
+ *
+ * - code: grpc_status_code code.
+ *
+ * It returns the converted tsi_result code.
+ */
+tsi_result alts_tsi_utils_convert_to_tsi_result(grpc_status_code code);
+
+/**
+ * This method deserializes a handshaker response returned from ALTS handshaker
+ * service.
+ *
+ * - bytes_received: data returned from ALTS handshaker service.
+ *
+ * It returns a deserialized handshaker response on success and nullptr on
+ * failure.
+ */
+grpc_gcp_handshaker_resp* alts_tsi_utils_deserialize_response(
+    grpc_byte_buffer* resp_buffer);
+
+#endif /* GRPC_CORE_TSI_ALTS_HANDSHAKER_ALTS_TSI_UTILS_H */
diff --git a/src/core/tsi/alts/handshaker/altscontext.pb.c b/src/core/tsi/alts/handshaker/altscontext.pb.c
new file mode 100644
index 0000000000..81a82f5992
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/altscontext.pb.c
@@ -0,0 +1,48 @@
+/* Automatically generated nanopb constant definitions */
+/* Generated by nanopb-0.3.7-dev */
+
+#include "src/core/tsi/alts/handshaker/altscontext.pb.h"
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+
+
+const pb_field_t grpc_gcp_AltsContext_fields[7] = {
+    PB_FIELD(  1, STRING  , OPTIONAL, CALLBACK, FIRST, grpc_gcp_AltsContext, application_protocol, application_protocol, 0),
+    PB_FIELD(  2, STRING  , OPTIONAL, CALLBACK, OTHER, grpc_gcp_AltsContext, record_protocol, application_protocol, 0),
+    PB_FIELD(  3, UENUM   , OPTIONAL, STATIC  , OTHER, grpc_gcp_AltsContext, security_level, record_protocol, 0),
+    PB_FIELD(  4, STRING  , OPTIONAL, CALLBACK, OTHER, grpc_gcp_AltsContext, peer_service_account, security_level, 0),
+    PB_FIELD(  5, STRING  , OPTIONAL, CALLBACK, OTHER, grpc_gcp_AltsContext, local_service_account, peer_service_account, 0),
+    PB_FIELD(  6, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_AltsContext, peer_rpc_versions, local_service_account, &grpc_gcp_RpcProtocolVersions_fields),
+    PB_LAST_FIELD
+};
+
+
+/* Check that field information fits in pb_field_t */
+#if !defined(PB_FIELD_32BIT)
+/* If you get an error here, it means that you need to define PB_FIELD_32BIT
+ * compile-time option. You can do that in pb.h or on compiler command line.
+ * 
+ * The reason you need to do this is that some of your messages contain tag
+ * numbers or field sizes that are larger than what can fit in 8 or 16 bit
+ * field descriptors.
+ */
+PB_STATIC_ASSERT((pb_membersize(grpc_gcp_AltsContext, peer_rpc_versions) < 65536), YOU_MUST_DEFINE_PB_FIELD_32BIT_FOR_MESSAGES_grpc_gcp_AltsContext)
+#endif
+
+#if !defined(PB_FIELD_16BIT) && !defined(PB_FIELD_32BIT)
+/* If you get an error here, it means that you need to define PB_FIELD_16BIT
+ * compile-time option. You can do that in pb.h or on compiler command line.
+ * 
+ * The reason you need to do this is that some of your messages contain tag
+ * numbers or field sizes that are larger than what can fit in the default
+ * 8 bit descriptors.
+ */
+PB_STATIC_ASSERT((pb_membersize(grpc_gcp_AltsContext, peer_rpc_versions) < 256), YOU_MUST_DEFINE_PB_FIELD_16BIT_FOR_MESSAGES_grpc_gcp_AltsContext)
+#endif
+
+
+/* @@protoc_insertion_point(eof) */
diff --git a/src/core/tsi/alts/handshaker/altscontext.pb.h b/src/core/tsi/alts/handshaker/altscontext.pb.h
new file mode 100644
index 0000000000..3e72d7f678
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/altscontext.pb.h
@@ -0,0 +1,64 @@
+/* Automatically generated nanopb header */
+/* Generated by nanopb-0.3.7-dev */
+
+#ifndef PB_GRPC_GCP_ALTSCONTEXT_PB_H_INCLUDED
+#define PB_GRPC_GCP_ALTSCONTEXT_PB_H_INCLUDED
+#include "third_party/nanopb/pb.h"
+#include "src/core/tsi/alts/handshaker/transport_security_common.pb.h"
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Struct definitions */
+typedef struct _grpc_gcp_AltsContext {
+    pb_callback_t application_protocol;
+    pb_callback_t record_protocol;
+    bool has_security_level;
+    grpc_gcp_SecurityLevel security_level;
+    pb_callback_t peer_service_account;
+    pb_callback_t local_service_account;
+    bool has_peer_rpc_versions;
+    grpc_gcp_RpcProtocolVersions peer_rpc_versions;
+/* @@protoc_insertion_point(struct:grpc_gcp_AltsContext) */
+} grpc_gcp_AltsContext;
+
+/* Default values for struct fields */
+
+/* Initializer values for message structs */
+#define grpc_gcp_AltsContext_init_default        {{{NULL}, NULL}, {{NULL}, NULL}, false, (grpc_gcp_SecurityLevel)0, {{NULL}, NULL}, {{NULL}, NULL}, false, grpc_gcp_RpcProtocolVersions_init_default}
+#define grpc_gcp_AltsContext_init_zero           {{{NULL}, NULL}, {{NULL}, NULL}, false, (grpc_gcp_SecurityLevel)0, {{NULL}, NULL}, {{NULL}, NULL}, false, grpc_gcp_RpcProtocolVersions_init_zero}
+
+/* Field tags (for use in manual encoding/decoding) */
+#define grpc_gcp_AltsContext_application_protocol_tag 1
+#define grpc_gcp_AltsContext_record_protocol_tag 2
+#define grpc_gcp_AltsContext_security_level_tag  3
+#define grpc_gcp_AltsContext_peer_service_account_tag 4
+#define grpc_gcp_AltsContext_local_service_account_tag 5
+#define grpc_gcp_AltsContext_peer_rpc_versions_tag 6
+
+/* Struct field encoding specification for nanopb */
+extern const pb_field_t grpc_gcp_AltsContext_fields[7];
+
+/* Maximum encoded size of messages (where known) */
+/* grpc_gcp_AltsContext_size depends on runtime parameters */
+
+/* Message IDs (where set with "msgid" option) */
+#ifdef PB_MSGID
+
+#define ALTSCONTEXT_MESSAGES \
+
+
+#endif
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+/* @@protoc_insertion_point(eof) */
+
+#endif
diff --git a/src/core/tsi/alts/handshaker/handshaker.pb.c b/src/core/tsi/alts/handshaker/handshaker.pb.c
new file mode 100644
index 0000000000..bd992dfa4a
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/handshaker.pb.c
@@ -0,0 +1,123 @@
+/* Automatically generated nanopb constant definitions */
+/* Generated by nanopb-0.3.7-dev */
+
+#include "src/core/tsi/alts/handshaker/handshaker.pb.h"
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+
+
+const pb_field_t grpc_gcp_Endpoint_fields[4] = {
+    PB_FIELD(  1, STRING  , OPTIONAL, CALLBACK, FIRST, grpc_gcp_Endpoint, ip_address, ip_address, 0),
+    PB_FIELD(  2, INT32   , OPTIONAL, STATIC  , OTHER, grpc_gcp_Endpoint, port, ip_address, 0),
+    PB_FIELD(  3, UENUM   , OPTIONAL, STATIC  , OTHER, grpc_gcp_Endpoint, protocol, port, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_Identity_fields[3] = {
+    PB_FIELD(  1, STRING  , OPTIONAL, CALLBACK, FIRST, grpc_gcp_Identity, service_account, service_account, 0),
+    PB_FIELD(  2, STRING  , OPTIONAL, CALLBACK, OTHER, grpc_gcp_Identity, hostname, service_account, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_StartClientHandshakeReq_fields[10] = {
+    PB_FIELD(  1, UENUM   , OPTIONAL, STATIC  , FIRST, grpc_gcp_StartClientHandshakeReq, handshake_security_protocol, handshake_security_protocol, 0),
+    PB_FIELD(  2, STRING  , REPEATED, CALLBACK, OTHER, grpc_gcp_StartClientHandshakeReq, application_protocols, handshake_security_protocol, 0),
+    PB_FIELD(  3, STRING  , REPEATED, CALLBACK, OTHER, grpc_gcp_StartClientHandshakeReq, record_protocols, application_protocols, 0),
+    PB_FIELD(  4, MESSAGE , REPEATED, CALLBACK, OTHER, grpc_gcp_StartClientHandshakeReq, target_identities, record_protocols, &grpc_gcp_Identity_fields),
+    PB_FIELD(  5, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_StartClientHandshakeReq, local_identity, target_identities, &grpc_gcp_Identity_fields),
+    PB_FIELD(  6, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_StartClientHandshakeReq, local_endpoint, local_identity, &grpc_gcp_Endpoint_fields),
+    PB_FIELD(  7, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_StartClientHandshakeReq, remote_endpoint, local_endpoint, &grpc_gcp_Endpoint_fields),
+    PB_FIELD(  8, STRING  , OPTIONAL, CALLBACK, OTHER, grpc_gcp_StartClientHandshakeReq, target_name, remote_endpoint, 0),
+    PB_FIELD(  9, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_StartClientHandshakeReq, rpc_versions, target_name, &grpc_gcp_RpcProtocolVersions_fields),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_ServerHandshakeParameters_fields[3] = {
+    PB_FIELD(  1, STRING  , REPEATED, CALLBACK, FIRST, grpc_gcp_ServerHandshakeParameters, record_protocols, record_protocols, 0),
+    PB_FIELD(  2, MESSAGE , REPEATED, CALLBACK, OTHER, grpc_gcp_ServerHandshakeParameters, local_identities, record_protocols, &grpc_gcp_Identity_fields),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_StartServerHandshakeReq_fields[7] = {
+    PB_FIELD(  1, STRING  , REPEATED, CALLBACK, FIRST, grpc_gcp_StartServerHandshakeReq, application_protocols, application_protocols, 0),
+    PB_FIELD(  2, MESSAGE , REPEATED, STATIC  , OTHER, grpc_gcp_StartServerHandshakeReq, handshake_parameters, application_protocols, &grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_fields),
+    PB_FIELD(  3, BYTES   , OPTIONAL, CALLBACK, OTHER, grpc_gcp_StartServerHandshakeReq, in_bytes, handshake_parameters, 0),
+    PB_FIELD(  4, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_StartServerHandshakeReq, local_endpoint, in_bytes, &grpc_gcp_Endpoint_fields),
+    PB_FIELD(  5, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_StartServerHandshakeReq, remote_endpoint, local_endpoint, &grpc_gcp_Endpoint_fields),
+    PB_FIELD(  6, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_StartServerHandshakeReq, rpc_versions, remote_endpoint, &grpc_gcp_RpcProtocolVersions_fields),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_fields[3] = {
+    PB_FIELD(  1, INT32   , OPTIONAL, STATIC  , FIRST, grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry, key, key, 0),
+    PB_FIELD(  2, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry, value, key, &grpc_gcp_ServerHandshakeParameters_fields),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_NextHandshakeMessageReq_fields[2] = {
+    PB_FIELD(  1, BYTES   , OPTIONAL, CALLBACK, FIRST, grpc_gcp_NextHandshakeMessageReq, in_bytes, in_bytes, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_HandshakerReq_fields[4] = {
+    PB_FIELD(  1, MESSAGE , OPTIONAL, STATIC  , FIRST, grpc_gcp_HandshakerReq, client_start, client_start, &grpc_gcp_StartClientHandshakeReq_fields),
+    PB_FIELD(  2, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerReq, server_start, client_start, &grpc_gcp_StartServerHandshakeReq_fields),
+    PB_FIELD(  3, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerReq, next, server_start, &grpc_gcp_NextHandshakeMessageReq_fields),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_HandshakerResult_fields[8] = {
+    PB_FIELD(  1, STRING  , OPTIONAL, CALLBACK, FIRST, grpc_gcp_HandshakerResult, application_protocol, application_protocol, 0),
+    PB_FIELD(  2, STRING  , OPTIONAL, CALLBACK, OTHER, grpc_gcp_HandshakerResult, record_protocol, application_protocol, 0),
+    PB_FIELD(  3, BYTES   , OPTIONAL, CALLBACK, OTHER, grpc_gcp_HandshakerResult, key_data, record_protocol, 0),
+    PB_FIELD(  4, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerResult, peer_identity, key_data, &grpc_gcp_Identity_fields),
+    PB_FIELD(  5, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerResult, local_identity, peer_identity, &grpc_gcp_Identity_fields),
+    PB_FIELD(  6, BOOL    , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerResult, keep_channel_open, local_identity, 0),
+    PB_FIELD(  7, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerResult, peer_rpc_versions, keep_channel_open, &grpc_gcp_RpcProtocolVersions_fields),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_HandshakerStatus_fields[3] = {
+    PB_FIELD(  1, UINT32  , OPTIONAL, STATIC  , FIRST, grpc_gcp_HandshakerStatus, code, code, 0),
+    PB_FIELD(  2, STRING  , OPTIONAL, CALLBACK, OTHER, grpc_gcp_HandshakerStatus, details, code, 0),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_HandshakerResp_fields[5] = {
+    PB_FIELD(  1, BYTES   , OPTIONAL, CALLBACK, FIRST, grpc_gcp_HandshakerResp, out_frames, out_frames, 0),
+    PB_FIELD(  2, UINT32  , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerResp, bytes_consumed, out_frames, 0),
+    PB_FIELD(  3, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerResp, result, bytes_consumed, &grpc_gcp_HandshakerResult_fields),
+    PB_FIELD(  4, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_HandshakerResp, status, result, &grpc_gcp_HandshakerStatus_fields),
+    PB_LAST_FIELD
+};
+
+
+/* Check that field information fits in pb_field_t */
+#if !defined(PB_FIELD_32BIT)
+/* If you get an error here, it means that you need to define PB_FIELD_32BIT
+ * compile-time option. You can do that in pb.h or on compiler command line.
+ * 
+ * The reason you need to do this is that some of your messages contain tag
+ * numbers or field sizes that are larger than what can fit in 8 or 16 bit
+ * field descriptors.
+ */
+PB_STATIC_ASSERT((pb_membersize(grpc_gcp_StartClientHandshakeReq, target_identities) < 65536 && pb_membersize(grpc_gcp_StartClientHandshakeReq, local_identity) < 65536 && pb_membersize(grpc_gcp_StartClientHandshakeReq, local_endpoint) < 65536 && pb_membersize(grpc_gcp_StartClientHandshakeReq, remote_endpoint) < 65536 && pb_membersize(grpc_gcp_StartClientHandshakeReq, rpc_versions) < 65536 && pb_membersize(grpc_gcp_ServerHandshakeParameters, local_identities) < 65536 && pb_membersize(grpc_gcp_StartServerHandshakeReq, handshake_parameters[0]) < 65536 && pb_membersize(grpc_gcp_StartServerHandshakeReq, local_endpoint) < 65536 && pb_membersize(grpc_gcp_StartServerHandshakeReq, remote_endpoint) < 65536 && pb_membersize(grpc_gcp_StartServerHandshakeReq, rpc_versions) < 65536 && pb_membersize(grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry, value) < 65536 && pb_membersize(grpc_gcp_HandshakerReq, client_start) < 65536 && pb_membersize(grpc_gcp_HandshakerReq, server_start) < 65536 && pb_membersize(grpc_gcp_HandshakerReq, next) < 65536 && pb_membersize(grpc_gcp_HandshakerResult, peer_identity) < 65536 && pb_membersize(grpc_gcp_HandshakerResult, local_identity) < 65536 && pb_membersize(grpc_gcp_HandshakerResult, peer_rpc_versions) < 65536 && pb_membersize(grpc_gcp_HandshakerResp, result) < 65536 && pb_membersize(grpc_gcp_HandshakerResp, status) < 65536), YOU_MUST_DEFINE_PB_FIELD_32BIT_FOR_MESSAGES_grpc_gcp_Endpoint_grpc_gcp_Identity_grpc_gcp_StartClientHandshakeReq_grpc_gcp_ServerHandshakeParameters_grpc_gcp_StartServerHandshakeReq_grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_grpc_gcp_NextHandshakeMessageReq_grpc_gcp_HandshakerReq_grpc_gcp_HandshakerResult_grpc_gcp_HandshakerStatus_grpc_gcp_HandshakerResp)
+#endif
+
+#if !defined(PB_FIELD_16BIT) && !defined(PB_FIELD_32BIT)
+/* If you get an error here, it means that you need to define PB_FIELD_16BIT
+ * compile-time option. You can do that in pb.h or on compiler command line.
+ * 
+ * The reason you need to do this is that some of your messages contain tag
+ * numbers or field sizes that are larger than what can fit in the default
+ * 8 bit descriptors.
+ */
+PB_STATIC_ASSERT((pb_membersize(grpc_gcp_StartClientHandshakeReq, target_identities) < 256 && pb_membersize(grpc_gcp_StartClientHandshakeReq, local_identity) < 256 && pb_membersize(grpc_gcp_StartClientHandshakeReq, local_endpoint) < 256 && pb_membersize(grpc_gcp_StartClientHandshakeReq, remote_endpoint) < 256 && pb_membersize(grpc_gcp_StartClientHandshakeReq, rpc_versions) < 256 && pb_membersize(grpc_gcp_ServerHandshakeParameters, local_identities) < 256 && pb_membersize(grpc_gcp_StartServerHandshakeReq, handshake_parameters[0]) < 256 && pb_membersize(grpc_gcp_StartServerHandshakeReq, local_endpoint) < 256 && pb_membersize(grpc_gcp_StartServerHandshakeReq, remote_endpoint) < 256 && pb_membersize(grpc_gcp_StartServerHandshakeReq, rpc_versions) < 256 && pb_membersize(grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry, value) < 256 && pb_membersize(grpc_gcp_HandshakerReq, client_start) < 256 && pb_membersize(grpc_gcp_HandshakerReq, server_start) < 256 && pb_membersize(grpc_gcp_HandshakerReq, next) < 256 && pb_membersize(grpc_gcp_HandshakerResult, peer_identity) < 256 && pb_membersize(grpc_gcp_HandshakerResult, local_identity) < 256 && pb_membersize(grpc_gcp_HandshakerResult, peer_rpc_versions) < 256 && pb_membersize(grpc_gcp_HandshakerResp, result) < 256 && pb_membersize(grpc_gcp_HandshakerResp, status) < 256), YOU_MUST_DEFINE_PB_FIELD_16BIT_FOR_MESSAGES_grpc_gcp_Endpoint_grpc_gcp_Identity_grpc_gcp_StartClientHandshakeReq_grpc_gcp_ServerHandshakeParameters_grpc_gcp_StartServerHandshakeReq_grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_grpc_gcp_NextHandshakeMessageReq_grpc_gcp_HandshakerReq_grpc_gcp_HandshakerResult_grpc_gcp_HandshakerStatus_grpc_gcp_HandshakerResp)
+#endif
+
+
+/* @@protoc_insertion_point(eof) */
diff --git a/src/core/tsi/alts/handshaker/handshaker.pb.h b/src/core/tsi/alts/handshaker/handshaker.pb.h
new file mode 100644
index 0000000000..0805a144de
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/handshaker.pb.h
@@ -0,0 +1,255 @@
+/* Automatically generated nanopb header */
+/* Generated by nanopb-0.3.7-dev */
+
+#ifndef PB_GRPC_GCP_HANDSHAKER_PB_H_INCLUDED
+#define PB_GRPC_GCP_HANDSHAKER_PB_H_INCLUDED
+#include "third_party/nanopb/pb.h"
+#include "src/core/tsi/alts/handshaker/transport_security_common.pb.h"
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Enum definitions */
+typedef enum _grpc_gcp_HandshakeProtocol {
+    grpc_gcp_HandshakeProtocol_HANDSHAKE_PROTOCOL_UNSPECIFIED = 0,
+    grpc_gcp_HandshakeProtocol_TLS = 1,
+    grpc_gcp_HandshakeProtocol_ALTS = 2
+} grpc_gcp_HandshakeProtocol;
+#define _grpc_gcp_HandshakeProtocol_MIN grpc_gcp_HandshakeProtocol_HANDSHAKE_PROTOCOL_UNSPECIFIED
+#define _grpc_gcp_HandshakeProtocol_MAX grpc_gcp_HandshakeProtocol_ALTS
+#define _grpc_gcp_HandshakeProtocol_ARRAYSIZE ((grpc_gcp_HandshakeProtocol)(grpc_gcp_HandshakeProtocol_ALTS+1))
+
+typedef enum _grpc_gcp_NetworkProtocol {
+    grpc_gcp_NetworkProtocol_NETWORK_PROTOCOL_UNSPECIFIED = 0,
+    grpc_gcp_NetworkProtocol_TCP = 1,
+    grpc_gcp_NetworkProtocol_UDP = 2
+} grpc_gcp_NetworkProtocol;
+#define _grpc_gcp_NetworkProtocol_MIN grpc_gcp_NetworkProtocol_NETWORK_PROTOCOL_UNSPECIFIED
+#define _grpc_gcp_NetworkProtocol_MAX grpc_gcp_NetworkProtocol_UDP
+#define _grpc_gcp_NetworkProtocol_ARRAYSIZE ((grpc_gcp_NetworkProtocol)(grpc_gcp_NetworkProtocol_UDP+1))
+
+/* Struct definitions */
+typedef struct _grpc_gcp_Identity {
+    pb_callback_t service_account;
+    pb_callback_t hostname;
+/* @@protoc_insertion_point(struct:grpc_gcp_Identity) */
+} grpc_gcp_Identity;
+
+typedef struct _grpc_gcp_NextHandshakeMessageReq {
+    pb_callback_t in_bytes;
+/* @@protoc_insertion_point(struct:grpc_gcp_NextHandshakeMessageReq) */
+} grpc_gcp_NextHandshakeMessageReq;
+
+typedef struct _grpc_gcp_ServerHandshakeParameters {
+    pb_callback_t record_protocols;
+    pb_callback_t local_identities;
+/* @@protoc_insertion_point(struct:grpc_gcp_ServerHandshakeParameters) */
+} grpc_gcp_ServerHandshakeParameters;
+
+typedef struct _grpc_gcp_Endpoint {
+    pb_callback_t ip_address;
+    bool has_port;
+    int32_t port;
+    bool has_protocol;
+    grpc_gcp_NetworkProtocol protocol;
+/* @@protoc_insertion_point(struct:grpc_gcp_Endpoint) */
+} grpc_gcp_Endpoint;
+
+typedef struct _grpc_gcp_HandshakerResult {
+    pb_callback_t application_protocol;
+    pb_callback_t record_protocol;
+    pb_callback_t key_data;
+    bool has_peer_identity;
+    grpc_gcp_Identity peer_identity;
+    bool has_local_identity;
+    grpc_gcp_Identity local_identity;
+    bool has_keep_channel_open;
+    bool keep_channel_open;
+    bool has_peer_rpc_versions;
+    grpc_gcp_RpcProtocolVersions peer_rpc_versions;
+/* @@protoc_insertion_point(struct:grpc_gcp_HandshakerResult) */
+} grpc_gcp_HandshakerResult;
+
+typedef struct _grpc_gcp_HandshakerStatus {
+    bool has_code;
+    uint32_t code;
+    pb_callback_t details;
+/* @@protoc_insertion_point(struct:grpc_gcp_HandshakerStatus) */
+} grpc_gcp_HandshakerStatus;
+
+typedef struct _grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry {
+    bool has_key;
+    int32_t key;
+    bool has_value;
+    grpc_gcp_ServerHandshakeParameters value;
+/* @@protoc_insertion_point(struct:grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry) */
+} grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry;
+
+typedef struct _grpc_gcp_HandshakerResp {
+    pb_callback_t out_frames;
+    bool has_bytes_consumed;
+    uint32_t bytes_consumed;
+    bool has_result;
+    grpc_gcp_HandshakerResult result;
+    bool has_status;
+    grpc_gcp_HandshakerStatus status;
+/* @@protoc_insertion_point(struct:grpc_gcp_HandshakerResp) */
+} grpc_gcp_HandshakerResp;
+
+typedef struct _grpc_gcp_StartClientHandshakeReq {
+    bool has_handshake_security_protocol;
+    grpc_gcp_HandshakeProtocol handshake_security_protocol;
+    pb_callback_t application_protocols;
+    pb_callback_t record_protocols;
+    pb_callback_t target_identities;
+    bool has_local_identity;
+    grpc_gcp_Identity local_identity;
+    bool has_local_endpoint;
+    grpc_gcp_Endpoint local_endpoint;
+    bool has_remote_endpoint;
+    grpc_gcp_Endpoint remote_endpoint;
+    pb_callback_t target_name;
+    bool has_rpc_versions;
+    grpc_gcp_RpcProtocolVersions rpc_versions;
+/* @@protoc_insertion_point(struct:grpc_gcp_StartClientHandshakeReq) */
+} grpc_gcp_StartClientHandshakeReq;
+
+typedef struct _grpc_gcp_StartServerHandshakeReq {
+    pb_callback_t application_protocols;
+    pb_size_t handshake_parameters_count;
+    grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry handshake_parameters[3];
+    pb_callback_t in_bytes;
+    bool has_local_endpoint;
+    grpc_gcp_Endpoint local_endpoint;
+    bool has_remote_endpoint;
+    grpc_gcp_Endpoint remote_endpoint;
+    bool has_rpc_versions;
+    grpc_gcp_RpcProtocolVersions rpc_versions;
+/* @@protoc_insertion_point(struct:grpc_gcp_StartServerHandshakeReq) */
+} grpc_gcp_StartServerHandshakeReq;
+
+typedef struct _grpc_gcp_HandshakerReq {
+    bool has_client_start;
+    grpc_gcp_StartClientHandshakeReq client_start;
+    bool has_server_start;
+    grpc_gcp_StartServerHandshakeReq server_start;
+    bool has_next;
+    grpc_gcp_NextHandshakeMessageReq next;
+/* @@protoc_insertion_point(struct:grpc_gcp_HandshakerReq) */
+} grpc_gcp_HandshakerReq;
+
+/* Default values for struct fields */
+
+/* Initializer values for message structs */
+#define grpc_gcp_Endpoint_init_default           {{{NULL}, NULL}, false, 0, false, (grpc_gcp_NetworkProtocol)0}
+#define grpc_gcp_Identity_init_default           {{{NULL}, NULL}, {{NULL}, NULL}}
+#define grpc_gcp_StartClientHandshakeReq_init_default {false, (grpc_gcp_HandshakeProtocol)0, {{NULL}, NULL}, {{NULL}, NULL}, {{NULL}, NULL}, false, grpc_gcp_Identity_init_default, false, grpc_gcp_Endpoint_init_default, false, grpc_gcp_Endpoint_init_default, {{NULL}, NULL}, false, grpc_gcp_RpcProtocolVersions_init_default}
+#define grpc_gcp_ServerHandshakeParameters_init_default {{{NULL}, NULL}, {{NULL}, NULL}}
+#define grpc_gcp_StartServerHandshakeReq_init_default {{{NULL}, NULL}, 0, {grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_init_default, grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_init_default, grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_init_default}, {{NULL}, NULL}, false, grpc_gcp_Endpoint_init_default, false, grpc_gcp_Endpoint_init_default, false, grpc_gcp_RpcProtocolVersions_init_default}
+#define grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_init_default {false, 0, false, grpc_gcp_ServerHandshakeParameters_init_default}
+#define grpc_gcp_NextHandshakeMessageReq_init_default {{{NULL}, NULL}}
+#define grpc_gcp_HandshakerReq_init_default      {false, grpc_gcp_StartClientHandshakeReq_init_default, false, grpc_gcp_StartServerHandshakeReq_init_default, false, grpc_gcp_NextHandshakeMessageReq_init_default}
+#define grpc_gcp_HandshakerResult_init_default   {{{NULL}, NULL}, {{NULL}, NULL}, {{NULL}, NULL}, false, grpc_gcp_Identity_init_default, false, grpc_gcp_Identity_init_default, false, 0, false, grpc_gcp_RpcProtocolVersions_init_default}
+#define grpc_gcp_HandshakerStatus_init_default   {false, 0, {{NULL}, NULL}}
+#define grpc_gcp_HandshakerResp_init_default     {{{NULL}, NULL}, false, 0, false, grpc_gcp_HandshakerResult_init_default, false, grpc_gcp_HandshakerStatus_init_default}
+#define grpc_gcp_Endpoint_init_zero              {{{NULL}, NULL}, false, 0, false, (grpc_gcp_NetworkProtocol)0}
+#define grpc_gcp_Identity_init_zero              {{{NULL}, NULL}, {{NULL}, NULL}}
+#define grpc_gcp_StartClientHandshakeReq_init_zero {false, (grpc_gcp_HandshakeProtocol)0, {{NULL}, NULL}, {{NULL}, NULL}, {{NULL}, NULL}, false, grpc_gcp_Identity_init_zero, false, grpc_gcp_Endpoint_init_zero, false, grpc_gcp_Endpoint_init_zero, {{NULL}, NULL}, false, grpc_gcp_RpcProtocolVersions_init_zero}
+#define grpc_gcp_ServerHandshakeParameters_init_zero {{{NULL}, NULL}, {{NULL}, NULL}}
+#define grpc_gcp_StartServerHandshakeReq_init_zero {{{NULL}, NULL}, 0, {grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_init_zero, grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_init_zero, grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_init_zero}, {{NULL}, NULL}, false, grpc_gcp_Endpoint_init_zero, false, grpc_gcp_Endpoint_init_zero, false, grpc_gcp_RpcProtocolVersions_init_zero}
+#define grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_init_zero {false, 0, false, grpc_gcp_ServerHandshakeParameters_init_zero}
+#define grpc_gcp_NextHandshakeMessageReq_init_zero {{{NULL}, NULL}}
+#define grpc_gcp_HandshakerReq_init_zero         {false, grpc_gcp_StartClientHandshakeReq_init_zero, false, grpc_gcp_StartServerHandshakeReq_init_zero, false, grpc_gcp_NextHandshakeMessageReq_init_zero}
+#define grpc_gcp_HandshakerResult_init_zero      {{{NULL}, NULL}, {{NULL}, NULL}, {{NULL}, NULL}, false, grpc_gcp_Identity_init_zero, false, grpc_gcp_Identity_init_zero, false, 0, false, grpc_gcp_RpcProtocolVersions_init_zero}
+#define grpc_gcp_HandshakerStatus_init_zero      {false, 0, {{NULL}, NULL}}
+#define grpc_gcp_HandshakerResp_init_zero        {{{NULL}, NULL}, false, 0, false, grpc_gcp_HandshakerResult_init_zero, false, grpc_gcp_HandshakerStatus_init_zero}
+
+/* Field tags (for use in manual encoding/decoding) */
+#define grpc_gcp_Identity_service_account_tag    1
+#define grpc_gcp_Identity_hostname_tag           2
+#define grpc_gcp_NextHandshakeMessageReq_in_bytes_tag 1
+#define grpc_gcp_ServerHandshakeParameters_record_protocols_tag 1
+#define grpc_gcp_ServerHandshakeParameters_local_identities_tag 2
+#define grpc_gcp_Endpoint_ip_address_tag         1
+#define grpc_gcp_Endpoint_port_tag               2
+#define grpc_gcp_Endpoint_protocol_tag           3
+#define grpc_gcp_HandshakerResult_application_protocol_tag 1
+#define grpc_gcp_HandshakerResult_record_protocol_tag 2
+#define grpc_gcp_HandshakerResult_key_data_tag   3
+#define grpc_gcp_HandshakerResult_peer_identity_tag 4
+#define grpc_gcp_HandshakerResult_local_identity_tag 5
+#define grpc_gcp_HandshakerResult_keep_channel_open_tag 6
+#define grpc_gcp_HandshakerResult_peer_rpc_versions_tag 7
+#define grpc_gcp_HandshakerStatus_code_tag       1
+#define grpc_gcp_HandshakerStatus_details_tag    2
+#define grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_key_tag 1
+#define grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_value_tag 2
+#define grpc_gcp_HandshakerResp_out_frames_tag   1
+#define grpc_gcp_HandshakerResp_bytes_consumed_tag 2
+#define grpc_gcp_HandshakerResp_result_tag       3
+#define grpc_gcp_HandshakerResp_status_tag       4
+#define grpc_gcp_StartClientHandshakeReq_handshake_security_protocol_tag 1
+#define grpc_gcp_StartClientHandshakeReq_application_protocols_tag 2
+#define grpc_gcp_StartClientHandshakeReq_record_protocols_tag 3
+#define grpc_gcp_StartClientHandshakeReq_target_identities_tag 4
+#define grpc_gcp_StartClientHandshakeReq_local_identity_tag 5
+#define grpc_gcp_StartClientHandshakeReq_local_endpoint_tag 6
+#define grpc_gcp_StartClientHandshakeReq_remote_endpoint_tag 7
+#define grpc_gcp_StartClientHandshakeReq_target_name_tag 8
+#define grpc_gcp_StartClientHandshakeReq_rpc_versions_tag 9
+#define grpc_gcp_StartServerHandshakeReq_application_protocols_tag 1
+#define grpc_gcp_StartServerHandshakeReq_handshake_parameters_tag 2
+#define grpc_gcp_StartServerHandshakeReq_in_bytes_tag 3
+#define grpc_gcp_StartServerHandshakeReq_local_endpoint_tag 4
+#define grpc_gcp_StartServerHandshakeReq_remote_endpoint_tag 5
+#define grpc_gcp_StartServerHandshakeReq_rpc_versions_tag 6
+#define grpc_gcp_HandshakerReq_client_start_tag  1
+#define grpc_gcp_HandshakerReq_server_start_tag  2
+#define grpc_gcp_HandshakerReq_next_tag          3
+
+/* Struct field encoding specification for nanopb */
+extern const pb_field_t grpc_gcp_Endpoint_fields[4];
+extern const pb_field_t grpc_gcp_Identity_fields[3];
+extern const pb_field_t grpc_gcp_StartClientHandshakeReq_fields[10];
+extern const pb_field_t grpc_gcp_ServerHandshakeParameters_fields[3];
+extern const pb_field_t grpc_gcp_StartServerHandshakeReq_fields[7];
+extern const pb_field_t grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_fields[3];
+extern const pb_field_t grpc_gcp_NextHandshakeMessageReq_fields[2];
+extern const pb_field_t grpc_gcp_HandshakerReq_fields[4];
+extern const pb_field_t grpc_gcp_HandshakerResult_fields[8];
+extern const pb_field_t grpc_gcp_HandshakerStatus_fields[3];
+extern const pb_field_t grpc_gcp_HandshakerResp_fields[5];
+
+/* Maximum encoded size of messages (where known) */
+/* grpc_gcp_Endpoint_size depends on runtime parameters */
+/* grpc_gcp_Identity_size depends on runtime parameters */
+/* grpc_gcp_StartClientHandshakeReq_size depends on runtime parameters */
+/* grpc_gcp_ServerHandshakeParameters_size depends on runtime parameters */
+/* grpc_gcp_StartServerHandshakeReq_size depends on runtime parameters */
+#define grpc_gcp_StartServerHandshakeReq_HandshakeParametersEntry_size (17 + grpc_gcp_ServerHandshakeParameters_size)
+/* grpc_gcp_NextHandshakeMessageReq_size depends on runtime parameters */
+#define grpc_gcp_HandshakerReq_size              (18 + grpc_gcp_StartClientHandshakeReq_size + grpc_gcp_StartServerHandshakeReq_size + grpc_gcp_NextHandshakeMessageReq_size)
+/* grpc_gcp_HandshakerResult_size depends on runtime parameters */
+/* grpc_gcp_HandshakerStatus_size depends on runtime parameters */
+/* grpc_gcp_HandshakerResp_size depends on runtime parameters */
+
+/* Message IDs (where set with "msgid" option) */
+#ifdef PB_MSGID
+
+#define HANDSHAKER_MESSAGES \
+
+
+#endif
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+/* @@protoc_insertion_point(eof) */
+
+#endif
diff --git a/src/core/tsi/alts/handshaker/proto/altscontext.proto b/src/core/tsi/alts/handshaker/proto/altscontext.proto
new file mode 100644
index 0000000000..d195b37e08
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/proto/altscontext.proto
@@ -0,0 +1,41 @@
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+import "transport_security_common.proto";
+
+package grpc.gcp;
+
+option java_package = "io.grpc.alts";
+
+message AltsContext {
+  // The application protocol negotiated for this connection.
+  string application_protocol = 1;
+
+  // The record protocol negotiated for this connection.
+  string record_protocol = 2;
+
+  // The security level of the created secure channel.
+  SecurityLevel security_level = 3;
+
+  // The peer service account.
+  string peer_service_account = 4;
+
+  // The local service account.
+  string local_service_account = 5;
+
+  // The RPC protocol versions supported by the peer.
+  RpcProtocolVersions peer_rpc_versions = 6;
+}
diff --git a/src/core/tsi/alts/handshaker/proto/handshaker.options b/src/core/tsi/alts/handshaker/proto/handshaker.options
new file mode 100644
index 0000000000..702ba3802a
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/proto/handshaker.options
@@ -0,0 +1,2 @@
+handshaker.proto no_unions:true
+grpc.gcp.StartServerHandshakeReq.handshake_parameters max_count:3
diff --git a/src/core/tsi/alts/handshaker/proto/handshaker.proto b/src/core/tsi/alts/handshaker/proto/handshaker.proto
new file mode 100644
index 0000000000..46b8b09eb0
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/proto/handshaker.proto
@@ -0,0 +1,220 @@
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+import "transport_security_common.proto";
+
+package grpc.gcp;
+
+option java_package = "io.grpc.alts";
+
+enum HandshakeProtocol {
+  // Default value.
+  HANDSHAKE_PROTOCOL_UNSPECIFIED = 0;
+
+  // TLS handshake protocol.
+  TLS = 1;
+
+  // Application Layer Transport Security handshake protocol.
+  ALTS = 2;
+}
+
+enum NetworkProtocol {
+  NETWORK_PROTOCOL_UNSPECIFIED = 0;
+  TCP = 1;
+  UDP = 2;
+}
+
+message Endpoint {
+  // IP address. It should contain an IPv4 or IPv6 string literal, e.g.
+  // "192.168.0.1" or "2001:db8::1".
+  string ip_address = 1;
+
+  // Port number.
+  int32 port = 2;
+
+  // Network protocol (e.g., TCP, UDP) associated with this endpoint.
+  NetworkProtocol protocol = 3;
+}
+
+message Identity {
+  oneof identity_oneof {
+    // Service account of a connection endpoint.
+    string service_account = 1;
+
+    // Hostname of a connection endpoint.
+    string hostname = 2;
+  }
+}
+
+message StartClientHandshakeReq {
+  // Handshake security protocol requested by the client.
+  HandshakeProtocol handshake_security_protocol = 1;
+
+  // The application protocols supported by the client, e.g., "h2" (for http2),
+  // "grpc".
+  repeated string application_protocols = 2;
+
+  // The record protocols supported by the client, e.g.,
+  // "ALTSRP_GCM_AES128".
+  repeated string record_protocols = 3;
+
+  // (Optional) Describes which server identities are acceptable by the client.
+  // If target identities are provided and none of them matches the peer
+  // identity of the server, handshake will fail.
+  repeated Identity target_identities = 4;
+
+  // (Optional) Application may specify a local identity. Otherwise, the
+  // handshaker chooses a default local identity.
+  Identity local_identity = 5;
+
+  // (Optional) Local endpoint information of the connection to the server,
+  // such as local IP address, port number, and network protocol.
+  Endpoint local_endpoint = 6;
+
+  // (Optional) Endpoint information of the remote server, such as IP address,
+  // port number, and network protocool.
+  Endpoint remote_endpoint = 7;
+
+  // (Optional) If target name is provided, a secure naming check is performed
+  // to verify that the peer authenticated identity is indeed authorized to run
+  // the target name.
+  string target_name = 8;
+
+  // (Optional) RPC protocol versions supported by the client.
+  RpcProtocolVersions rpc_versions = 9;
+}
+
+message ServerHandshakeParameters {
+  // The record protocols supported by the server, e.g.,
+  // "ALTSRP_GCM_AES128".
+  repeated string record_protocols = 1;
+
+  // (Optional) A list of local identities supported by the server, if
+  // specified. Otherwise, the handshaker chooses a default local identity.
+  repeated Identity local_identities = 2;
+}
+
+message StartServerHandshakeReq {
+  // The application protocols supported by the server, e.g., "h2" (for http2),
+  // "grpc".
+  repeated string application_protocols = 1;
+
+  // Handshake parameters (record protocols and local identities supported by
+  // the server) mapped by the handshake protocol. Each handshake security
+  // protocol (e.g., TLS or ALTS) has its own set of record protocols and local
+  // identities. Since protobuf does not support enum as key to the map, the key
+  // to handshake_parameters is the integer value of HandshakeProtocol enum.
+  map<int32, ServerHandshakeParameters> handshake_parameters = 2;
+
+  // Bytes in out_frames returned from the peer's HandshakerResp. It is possible
+  // that the peer's out_frames are split into multiple HandshakReq messages.
+  bytes in_bytes = 3;
+
+  // (Optional) Local endpoint information of the connection to the client,
+  // such as local IP address, port number, and network protocol.
+  Endpoint local_endpoint = 4;
+
+  // (Optional) Endpoint information of the remote client, such as IP address,
+  // port number, and network protocool.
+  Endpoint remote_endpoint = 5;
+
+  // (Optional) RPC protocol versions supported by the server.
+  RpcProtocolVersions rpc_versions = 6;
+}
+
+message NextHandshakeMessageReq {
+  // Bytes in out_frames returned from the peer's HandshakerResp. It is possible
+  // that the peer's out_frames are split into multiple NextHandshakerMessageReq
+  // messages.
+  bytes in_bytes = 1;
+}
+
+message HandshakerReq {
+  oneof req_oneof {
+    // The start client handshake request message.
+    StartClientHandshakeReq client_start = 1;
+
+    // The start server handshake request message.
+    StartServerHandshakeReq server_start = 2;
+
+    // The next handshake request message.
+    NextHandshakeMessageReq next = 3;
+  }
+}
+
+message HandshakerResult {
+  // The application protocol negotiated for this connection.
+  string application_protocol = 1;
+
+  // The record protocol negotiated for this connection.
+  string record_protocol = 2;
+
+  // Cryptographic key data. The key data may be more than the key length
+  // required for the record protocol, thus the client of the handshaker
+  // service needs to truncate the key data into the right key length.
+  bytes key_data = 3;
+
+  // The authenticated identity of the peer.
+  Identity peer_identity = 4;
+
+  // The local identity used in the handshake.
+  Identity local_identity = 5;
+
+  // Indicate whether the handshaker service client should keep the channel
+  // between the handshaker service open, e.g., in order to handle
+  // post-handshake messages in the future.
+  bool keep_channel_open = 6;
+
+  // The RPC protocol versions supported by the peer.
+  RpcProtocolVersions peer_rpc_versions = 7;
+}
+
+message HandshakerStatus {
+  // The status code. This could be the gRPC status code.
+  uint32 code = 1;
+
+  // The status details.
+  string details = 2;
+}
+
+message HandshakerResp {
+  // Frames to be given to the peer for the NextHandshakeMessageReq. May be
+  // empty if no out_frames have to be sent to the peer or if in_bytes in the
+  // HandshakerReq are incomplete. All the non-empty out frames must be sent to
+  // the peer even if the handshaker status is not OK as these frames may
+  // contain the alert frames.
+  bytes out_frames = 1;
+
+  // Number of bytes in the in_bytes consumed by the handshaker. It is possible
+  // that part of in_bytes in HandshakerReq was unrelated to the handshake
+  // process.
+  uint32 bytes_consumed = 2;
+
+  // This is set iff the handshake was successful. out_frames may still be set
+  // to frames that needs to be forwarded to the peer.
+  HandshakerResult result = 3;
+
+  // Status of the handshaker.
+  HandshakerStatus status = 4;
+}
+
+service HandshakerService {
+  // Accepts a stream of handshaker request, returning a stream of handshaker
+  // response.
+  rpc DoHandshake(stream HandshakerReq)
+      returns (stream HandshakerResp) {
+  }
+}
diff --git a/src/core/tsi/alts/handshaker/proto/transport_security_common.proto b/src/core/tsi/alts/handshaker/proto/transport_security_common.proto
new file mode 100644
index 0000000000..41983ab9f9
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/proto/transport_security_common.proto
@@ -0,0 +1,40 @@
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package grpc.gcp;
+
+option java_package = "io.grpc.alts";
+
+// The security level of the created channel. The list is sorted in increasing
+// level of security. This order must always be maintained.
+enum SecurityLevel {
+  SECURITY_NONE = 0;
+  INTEGRITY_ONLY = 1;
+  INTEGRITY_AND_PRIVACY = 2;
+}
+
+// Max and min supported RPC protocol versions.
+message RpcProtocolVersions {
+  // RPC version contains a major version and a minor version.
+  message Version {
+    uint32 major = 1;
+    uint32 minor = 2;
+  }
+  // Maximum supported RPC version.
+  Version max_rpc_version = 1;
+  // Minimum supported RPC version.
+  Version min_rpc_version = 2;
+}
diff --git a/src/core/tsi/alts/handshaker/transport_security_common.pb.c b/src/core/tsi/alts/handshaker/transport_security_common.pb.c
new file mode 100644
index 0000000000..6063c7625e
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/transport_security_common.pb.c
@@ -0,0 +1,50 @@
+/* Automatically generated nanopb constant definitions */
+/* Generated by nanopb-0.3.7-dev */
+
+#include "src/core/tsi/alts/handshaker/transport_security_common.pb.h"
+
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+
+
+const pb_field_t grpc_gcp_RpcProtocolVersions_fields[3] = {
+    PB_FIELD(  1, MESSAGE , OPTIONAL, STATIC  , FIRST, grpc_gcp_RpcProtocolVersions, max_rpc_version, max_rpc_version, &grpc_gcp_RpcProtocolVersions_Version_fields),
+    PB_FIELD(  2, MESSAGE , OPTIONAL, STATIC  , OTHER, grpc_gcp_RpcProtocolVersions, min_rpc_version, max_rpc_version, &grpc_gcp_RpcProtocolVersions_Version_fields),
+    PB_LAST_FIELD
+};
+
+const pb_field_t grpc_gcp_RpcProtocolVersions_Version_fields[3] = {
+    PB_FIELD(  1, UINT32  , OPTIONAL, STATIC  , FIRST, grpc_gcp_RpcProtocolVersions_Version, major, major, 0),
+    PB_FIELD(  2, UINT32  , OPTIONAL, STATIC  , OTHER, grpc_gcp_RpcProtocolVersions_Version, minor, major, 0),
+    PB_LAST_FIELD
+};
+
+
+/* Check that field information fits in pb_field_t */
+#if !defined(PB_FIELD_32BIT)
+/* If you get an error here, it means that you need to define PB_FIELD_32BIT
+ * compile-time option. You can do that in pb.h or on compiler command line.
+ * 
+ * The reason you need to do this is that some of your messages contain tag
+ * numbers or field sizes that are larger than what can fit in 8 or 16 bit
+ * field descriptors.
+ */
+PB_STATIC_ASSERT((pb_membersize(grpc_gcp_RpcProtocolVersions, max_rpc_version) < 65536 && pb_membersize(grpc_gcp_RpcProtocolVersions, min_rpc_version) < 65536), YOU_MUST_DEFINE_PB_FIELD_32BIT_FOR_MESSAGES_grpc_gcp_RpcProtocolVersions_grpc_gcp_RpcProtocolVersions_Version)
+#endif
+
+#if !defined(PB_FIELD_16BIT) && !defined(PB_FIELD_32BIT)
+/* If you get an error here, it means that you need to define PB_FIELD_16BIT
+ * compile-time option. You can do that in pb.h or on compiler command line.
+ * 
+ * The reason you need to do this is that some of your messages contain tag
+ * numbers or field sizes that are larger than what can fit in the default
+ * 8 bit descriptors.
+ */
+PB_STATIC_ASSERT((pb_membersize(grpc_gcp_RpcProtocolVersions, max_rpc_version) < 256 && pb_membersize(grpc_gcp_RpcProtocolVersions, min_rpc_version) < 256), YOU_MUST_DEFINE_PB_FIELD_16BIT_FOR_MESSAGES_grpc_gcp_RpcProtocolVersions_grpc_gcp_RpcProtocolVersions_Version)
+#endif
+
+
+/* @@protoc_insertion_point(eof) */
diff --git a/src/core/tsi/alts/handshaker/transport_security_common.pb.h b/src/core/tsi/alts/handshaker/transport_security_common.pb.h
new file mode 100644
index 0000000000..49096dffa3
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/transport_security_common.pb.h
@@ -0,0 +1,78 @@
+/* Automatically generated nanopb header */
+/* Generated by nanopb-0.3.7-dev */
+
+#ifndef PB_GRPC_GCP_TRANSPORT_SECURITY_COMMON_PB_H_INCLUDED
+#define PB_GRPC_GCP_TRANSPORT_SECURITY_COMMON_PB_H_INCLUDED
+#include "third_party/nanopb/pb.h"
+/* @@protoc_insertion_point(includes) */
+#if PB_PROTO_HEADER_VERSION != 30
+#error Regenerate this file with the current version of nanopb generator.
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Enum definitions */
+typedef enum _grpc_gcp_SecurityLevel {
+    grpc_gcp_SecurityLevel_SECURITY_NONE = 0,
+    grpc_gcp_SecurityLevel_INTEGRITY_ONLY = 1,
+    grpc_gcp_SecurityLevel_INTEGRITY_AND_PRIVACY = 2
+} grpc_gcp_SecurityLevel;
+#define _grpc_gcp_SecurityLevel_MIN grpc_gcp_SecurityLevel_SECURITY_NONE
+#define _grpc_gcp_SecurityLevel_MAX grpc_gcp_SecurityLevel_INTEGRITY_AND_PRIVACY
+#define _grpc_gcp_SecurityLevel_ARRAYSIZE ((grpc_gcp_SecurityLevel)(grpc_gcp_SecurityLevel_INTEGRITY_AND_PRIVACY+1))
+
+/* Struct definitions */
+typedef struct _grpc_gcp_RpcProtocolVersions_Version {
+    bool has_major;
+    uint32_t major;
+    bool has_minor;
+    uint32_t minor;
+/* @@protoc_insertion_point(struct:grpc_gcp_RpcProtocolVersions_Version) */
+} grpc_gcp_RpcProtocolVersions_Version;
+
+typedef struct _grpc_gcp_RpcProtocolVersions {
+    bool has_max_rpc_version;
+    grpc_gcp_RpcProtocolVersions_Version max_rpc_version;
+    bool has_min_rpc_version;
+    grpc_gcp_RpcProtocolVersions_Version min_rpc_version;
+/* @@protoc_insertion_point(struct:grpc_gcp_RpcProtocolVersions) */
+} grpc_gcp_RpcProtocolVersions;
+
+/* Default values for struct fields */
+
+/* Initializer values for message structs */
+#define grpc_gcp_RpcProtocolVersions_init_default {false, grpc_gcp_RpcProtocolVersions_Version_init_default, false, grpc_gcp_RpcProtocolVersions_Version_init_default}
+#define grpc_gcp_RpcProtocolVersions_Version_init_default {false, 0, false, 0}
+#define grpc_gcp_RpcProtocolVersions_init_zero   {false, grpc_gcp_RpcProtocolVersions_Version_init_zero, false, grpc_gcp_RpcProtocolVersions_Version_init_zero}
+#define grpc_gcp_RpcProtocolVersions_Version_init_zero {false, 0, false, 0}
+
+/* Field tags (for use in manual encoding/decoding) */
+#define grpc_gcp_RpcProtocolVersions_Version_major_tag 1
+#define grpc_gcp_RpcProtocolVersions_Version_minor_tag 2
+#define grpc_gcp_RpcProtocolVersions_max_rpc_version_tag 1
+#define grpc_gcp_RpcProtocolVersions_min_rpc_version_tag 2
+
+/* Struct field encoding specification for nanopb */
+extern const pb_field_t grpc_gcp_RpcProtocolVersions_fields[3];
+extern const pb_field_t grpc_gcp_RpcProtocolVersions_Version_fields[3];
+
+/* Maximum encoded size of messages (where known) */
+#define grpc_gcp_RpcProtocolVersions_size        28
+#define grpc_gcp_RpcProtocolVersions_Version_size 12
+
+/* Message IDs (where set with "msgid" option) */
+#ifdef PB_MSGID
+
+#define TRANSPORT_SECURITY_COMMON_MESSAGES \
+
+
+#endif
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+/* @@protoc_insertion_point(eof) */
+
+#endif
diff --git a/src/core/tsi/alts/handshaker/transport_security_common_api.cc b/src/core/tsi/alts/handshaker/transport_security_common_api.cc
new file mode 100644
index 0000000000..8a7edb53d4
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/transport_security_common_api.cc
@@ -0,0 +1,196 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/handshaker/transport_security_common_api.h"
+
+bool grpc_gcp_rpc_protocol_versions_set_max(
+    grpc_gcp_rpc_protocol_versions* versions, uint32_t max_major,
+    uint32_t max_minor) {
+  if (versions == nullptr) {
+    gpr_log(GPR_ERROR,
+            "versions is nullptr in "
+            "grpc_gcp_rpc_protocol_versions_set_max().");
+    return false;
+  }
+  versions->has_max_rpc_version = true;
+  versions->max_rpc_version.has_major = true;
+  versions->max_rpc_version.has_minor = true;
+  versions->max_rpc_version.major = max_major;
+  versions->max_rpc_version.minor = max_minor;
+  return true;
+}
+
+bool grpc_gcp_rpc_protocol_versions_set_min(
+    grpc_gcp_rpc_protocol_versions* versions, uint32_t min_major,
+    uint32_t min_minor) {
+  if (versions == nullptr) {
+    gpr_log(GPR_ERROR,
+            "versions is nullptr in "
+            "grpc_gcp_rpc_protocol_versions_set_min().");
+    return false;
+  }
+  versions->has_min_rpc_version = true;
+  versions->min_rpc_version.has_major = true;
+  versions->min_rpc_version.has_minor = true;
+  versions->min_rpc_version.major = min_major;
+  versions->min_rpc_version.minor = min_minor;
+  return true;
+}
+
+size_t grpc_gcp_rpc_protocol_versions_encode_length(
+    const grpc_gcp_rpc_protocol_versions* versions) {
+  if (versions == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to "
+            "grpc_gcp_rpc_protocol_versions_encode_length().");
+    return 0;
+  }
+  pb_ostream_t size_stream;
+  memset(&size_stream, 0, sizeof(pb_ostream_t));
+  if (!pb_encode(&size_stream, grpc_gcp_RpcProtocolVersions_fields, versions)) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&size_stream));
+    return 0;
+  }
+  return size_stream.bytes_written;
+}
+
+bool grpc_gcp_rpc_protocol_versions_encode_to_raw_bytes(
+    const grpc_gcp_rpc_protocol_versions* versions, uint8_t* bytes,
+    size_t bytes_length) {
+  if (versions == nullptr || bytes == nullptr || bytes_length == 0) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to "
+            "grpc_gcp_rpc_protocol_versions_encode_to_raw_bytes().");
+    return false;
+  }
+  pb_ostream_t output_stream = pb_ostream_from_buffer(bytes, bytes_length);
+  if (!pb_encode(&output_stream, grpc_gcp_RpcProtocolVersions_fields,
+                 versions)) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&output_stream));
+    return false;
+  }
+  return true;
+}
+
+bool grpc_gcp_rpc_protocol_versions_encode(
+    const grpc_gcp_rpc_protocol_versions* versions, grpc_slice* slice) {
+  if (versions == nullptr || slice == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to "
+            "grpc_gcp_rpc_protocol_versions_encode().");
+    return false;
+  }
+  size_t encoded_length =
+      grpc_gcp_rpc_protocol_versions_encode_length(versions);
+  if (encoded_length == 0) return false;
+  *slice = grpc_slice_malloc(encoded_length);
+  return grpc_gcp_rpc_protocol_versions_encode_to_raw_bytes(
+      versions, GRPC_SLICE_START_PTR(*slice), encoded_length);
+}
+
+bool grpc_gcp_rpc_protocol_versions_decode(
+    grpc_slice slice, grpc_gcp_rpc_protocol_versions* versions) {
+  if (versions == nullptr) {
+    gpr_log(GPR_ERROR,
+            "version is nullptr in "
+            "grpc_gcp_rpc_protocol_versions_decode().");
+    return false;
+  }
+  pb_istream_t stream = pb_istream_from_buffer(GRPC_SLICE_START_PTR(slice),
+                                               GRPC_SLICE_LENGTH(slice));
+  if (!pb_decode(&stream, grpc_gcp_RpcProtocolVersions_fields, versions)) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
+    return false;
+  }
+  return true;
+}
+
+bool grpc_gcp_rpc_protocol_versions_copy(
+    const grpc_gcp_rpc_protocol_versions* src,
+    grpc_gcp_rpc_protocol_versions* dst) {
+  if ((src == nullptr && dst != nullptr) ||
+      (src != nullptr && dst == nullptr)) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_rpc_protocol_versions_copy().");
+    return false;
+  }
+  if (src == nullptr) {
+    return true;
+  }
+  grpc_gcp_rpc_protocol_versions_set_max(dst, src->max_rpc_version.major,
+                                         src->max_rpc_version.minor);
+  grpc_gcp_rpc_protocol_versions_set_min(dst, src->min_rpc_version.major,
+                                         src->min_rpc_version.minor);
+  return true;
+}
+
+namespace grpc_core {
+namespace internal {
+
+int grpc_gcp_rpc_protocol_version_compare(
+    const grpc_gcp_rpc_protocol_versions_version* v1,
+    const grpc_gcp_rpc_protocol_versions_version* v2) {
+  if ((v1->major > v2->major) ||
+      (v1->major == v2->major && v1->minor > v2->minor)) {
+    return 1;
+  }
+  if ((v1->major < v2->major) ||
+      (v1->major == v2->major && v1->minor < v2->minor)) {
+    return -1;
+  }
+  return 0;
+}
+
+}  // namespace internal
+}  // namespace grpc_core
+
+bool grpc_gcp_rpc_protocol_versions_check(
+    const grpc_gcp_rpc_protocol_versions* local_versions,
+    const grpc_gcp_rpc_protocol_versions* peer_versions,
+    grpc_gcp_rpc_protocol_versions_version* highest_common_version) {
+  if (local_versions == nullptr || peer_versions == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid arguments to "
+            "grpc_gcp_rpc_protocol_versions_check().");
+    return false;
+  }
+  /* max_common_version is MIN(local.max, peer.max) */
+  const grpc_gcp_rpc_protocol_versions_version* max_common_version =
+      grpc_core::internal::grpc_gcp_rpc_protocol_version_compare(
+          &local_versions->max_rpc_version, &peer_versions->max_rpc_version) > 0
+          ? &peer_versions->max_rpc_version
+          : &local_versions->max_rpc_version;
+  /* min_common_version is MAX(local.min, peer.min) */
+  const grpc_gcp_rpc_protocol_versions_version* min_common_version =
+      grpc_core::internal::grpc_gcp_rpc_protocol_version_compare(
+          &local_versions->min_rpc_version, &peer_versions->min_rpc_version) > 0
+          ? &local_versions->min_rpc_version
+          : &peer_versions->min_rpc_version;
+  bool result = grpc_core::internal::grpc_gcp_rpc_protocol_version_compare(
+                    max_common_version, min_common_version) >= 0
+                    ? true
+                    : false;
+  if (result && highest_common_version != nullptr) {
+    memcpy(highest_common_version, max_common_version,
+           sizeof(grpc_gcp_rpc_protocol_versions_version));
+  }
+  return result;
+}
diff --git a/src/core/tsi/alts/handshaker/transport_security_common_api.h b/src/core/tsi/alts/handshaker/transport_security_common_api.h
new file mode 100644
index 0000000000..68228cb3b5
--- /dev/null
+++ b/src/core/tsi/alts/handshaker/transport_security_common_api.h
@@ -0,0 +1,163 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_HANDSHAKER_TRANSPORT_SECURITY_COMMON_API_H
+#define GRPC_CORE_TSI_ALTS_HANDSHAKER_TRANSPORT_SECURITY_COMMON_API_H
+
+#include <grpc/support/port_platform.h>
+
+#include "third_party/nanopb/pb_decode.h"
+#include "third_party/nanopb/pb_encode.h"
+
+#include <grpc/slice.h>
+#include <grpc/slice_buffer.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/tsi/alts/handshaker/transport_security_common.pb.h"
+
+typedef grpc_gcp_RpcProtocolVersions grpc_gcp_rpc_protocol_versions;
+
+typedef grpc_gcp_RpcProtocolVersions_Version
+    grpc_gcp_rpc_protocol_versions_version;
+
+/**
+ * This method sets the value for max_rpc_versions field of rpc protocol
+ * versions.
+ *
+ * - versions: an rpc protocol version instance.
+ * - max_major: a major version of maximum supported RPC version.
+ * - max_minor: a minor version of maximum supported RPC version.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_rpc_protocol_versions_set_max(
+    grpc_gcp_rpc_protocol_versions* versions, uint32_t max_major,
+    uint32_t max_minor);
+
+/**
+ * This method sets the value for min_rpc_versions field of rpc protocol
+ * versions.
+ *
+ * - versions: an rpc protocol version instance.
+ * - min_major: a major version of minimum supported RPC version.
+ * - min_minor: a minor version of minimum supported RPC version.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_rpc_protocol_versions_set_min(
+    grpc_gcp_rpc_protocol_versions* versions, uint32_t min_major,
+    uint32_t min_minor);
+
+/**
+ * This method computes serialized byte length of rpc protocol versions.
+ *
+ * - versions: an rpc protocol versions instance.
+ *
+ * The method returns serialized byte length. It returns 0 on failure.
+ */
+size_t grpc_gcp_rpc_protocol_versions_encode_length(
+    const grpc_gcp_rpc_protocol_versions* versions);
+
+/**
+ * This method serializes rpc protocol versions and writes the result to
+ * the memory buffer provided by the caller. Caller is responsible for
+ * allocating sufficient memory to store the serialized data.
+ *
+ * - versions: an rpc protocol versions instance.
+ * - bytes: bytes buffer where the result will be written to.
+ * - bytes_length: length of the bytes buffer.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_rpc_protocol_versions_encode_to_raw_bytes(
+    const grpc_gcp_rpc_protocol_versions* versions, uint8_t* bytes,
+    size_t bytes_length);
+
+/**
+ * This method serializes an rpc protocol version and returns serialized rpc
+ * versions in grpc slice.
+ *
+ * - versions: an rpc protocol versions instance.
+ * - slice: grpc slice where the serialized result will be written.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_rpc_protocol_versions_encode(
+    const grpc_gcp_rpc_protocol_versions* versions, grpc_slice* slice);
+
+/**
+ * This method de-serializes input in grpc slice form and stores the result
+ * in rpc protocol versions.
+ *
+ * - slice: a data stream containing a serialized rpc protocol version.
+ * - versions: an rpc protocol version instance used to hold de-serialized
+ *   result.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_rpc_protocol_versions_decode(
+    grpc_slice slice, grpc_gcp_rpc_protocol_versions* versions);
+
+/**
+ * This method performs a deep copy operation on rpc protocol versions
+ * instance.
+ *
+ * - src: rpc protocol versions instance that needs to be copied.
+ * - dst: rpc protocol versions instance that stores the copied result.
+ *
+ * The method returns true on success and false otherwise.
+ */
+bool grpc_gcp_rpc_protocol_versions_copy(
+    const grpc_gcp_rpc_protocol_versions* src,
+    grpc_gcp_rpc_protocol_versions* dst);
+
+/**
+ * This method performs a version check between local and peer rpc protocol
+ * versions.
+ *
+ * - local_versions: local rpc protocol versions instance.
+ * - peer_versions: peer rpc protocol versions instance.
+ * - highest_common_version: an output parameter that will store the highest
+ *   common rpc protocol version both parties agreed on.
+ *
+ * The method returns true if the check passes which means both parties agreed
+ * on a common rpc protocol to use, and false otherwise.
+ */
+bool grpc_gcp_rpc_protocol_versions_check(
+    const grpc_gcp_rpc_protocol_versions* local_versions,
+    const grpc_gcp_rpc_protocol_versions* peer_versions,
+    grpc_gcp_rpc_protocol_versions_version* highest_common_version);
+
+namespace grpc_core {
+namespace internal {
+
+/**
+ * Exposed for testing only.
+ * The method returns 0 if v1 = v2,
+ *            returns 1 if v1 > v2,
+ *            returns -1 if v1 < v2.
+ */
+int grpc_gcp_rpc_protocol_version_compare(
+    const grpc_gcp_rpc_protocol_versions_version* v1,
+    const grpc_gcp_rpc_protocol_versions_version* v2);
+
+}  // namespace internal
+}  // namespace grpc_core
+
+#endif /* GRPC_CORE_TSI_ALTS_HANDSHAKER_TRANSPORT_SECURITY_COMMON_API_H */
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.cc b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.cc
new file mode 100644
index 0000000000..7ba03eb7f0
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.cc
@@ -0,0 +1,180 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.h"
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/lib/slice/slice_internal.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.h"
+
+/* Main struct for alts_grpc_integrity_only_record_protocol.  */
+typedef struct alts_grpc_integrity_only_record_protocol {
+  alts_grpc_record_protocol base;
+  grpc_slice_buffer data_sb;
+  unsigned char* tag_buf;
+} alts_grpc_integrity_only_record_protocol;
+
+/* --- alts_grpc_record_protocol methods implementation. --- */
+
+static tsi_result alts_grpc_integrity_only_protect(
+    alts_grpc_record_protocol* rp, grpc_slice_buffer* unprotected_slices,
+    grpc_slice_buffer* protected_slices) {
+  /* Input sanity check.  */
+  if (rp == nullptr || unprotected_slices == nullptr ||
+      protected_slices == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to alts_grpc_record_protocol protect.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  /* Allocates memory for header and tag slices.  */
+  grpc_slice header_slice = GRPC_SLICE_MALLOC(rp->header_length);
+  grpc_slice tag_slice = GRPC_SLICE_MALLOC(rp->tag_length);
+  /* Calls alts_iovec_record_protocol protect.  */
+  char* error_details = nullptr;
+  iovec_t header_iovec = {GRPC_SLICE_START_PTR(header_slice),
+                          GRPC_SLICE_LENGTH(header_slice)};
+  iovec_t tag_iovec = {GRPC_SLICE_START_PTR(tag_slice),
+                       GRPC_SLICE_LENGTH(tag_slice)};
+  alts_grpc_record_protocol_convert_slice_buffer_to_iovec(rp,
+                                                          unprotected_slices);
+  grpc_status_code status = alts_iovec_record_protocol_integrity_only_protect(
+      rp->iovec_rp, rp->iovec_buf, unprotected_slices->count, header_iovec,
+      tag_iovec, &error_details);
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "Failed to protect, %s", error_details);
+    gpr_free(error_details);
+    return TSI_INTERNAL_ERROR;
+  }
+  /* Appends result to protected_slices.  */
+  grpc_slice_buffer_add(protected_slices, header_slice);
+  grpc_slice_buffer_move_into(unprotected_slices, protected_slices);
+  grpc_slice_buffer_add(protected_slices, tag_slice);
+  return TSI_OK;
+}
+
+static tsi_result alts_grpc_integrity_only_unprotect(
+    alts_grpc_record_protocol* rp, grpc_slice_buffer* protected_slices,
+    grpc_slice_buffer* unprotected_slices) {
+  /* Input sanity check.  */
+  if (rp == nullptr || protected_slices == nullptr ||
+      unprotected_slices == nullptr) {
+    gpr_log(
+        GPR_ERROR,
+        "Invalid nullptr arguments to alts_grpc_record_protocol unprotect.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  if (protected_slices->length < rp->header_length + rp->tag_length) {
+    gpr_log(GPR_ERROR, "Protected slices do not have sufficient data.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  /* In this method, rp points to alts_grpc_record_protocol struct
+   * and integrity_only_record_protocol points to
+   * alts_grpc_integrity_only_record_protocol struct.  */
+  alts_grpc_integrity_only_record_protocol* integrity_only_record_protocol =
+      reinterpret_cast<alts_grpc_integrity_only_record_protocol*>(rp);
+  /* Strips frame header from protected slices.  */
+  grpc_slice_buffer_reset_and_unref_internal(&rp->header_sb);
+  grpc_slice_buffer_move_first(protected_slices, rp->header_length,
+                               &rp->header_sb);
+  GPR_ASSERT(rp->header_sb.length == rp->header_length);
+  iovec_t header_iovec = alts_grpc_record_protocol_get_header_iovec(rp);
+  /* Moves protected slices data to data_sb and leaves the remaining tag.  */
+  grpc_slice_buffer_reset_and_unref_internal(
+      &integrity_only_record_protocol->data_sb);
+  grpc_slice_buffer_move_first(protected_slices,
+                               protected_slices->length - rp->tag_length,
+                               &integrity_only_record_protocol->data_sb);
+  GPR_ASSERT(protected_slices->length == rp->tag_length);
+  iovec_t tag_iovec = {nullptr, rp->tag_length};
+  if (protected_slices->count == 1) {
+    tag_iovec.iov_base = GRPC_SLICE_START_PTR(protected_slices->slices[0]);
+  } else {
+    /* Frame tag is in multiple slices, copies the tag bytes from slice
+     * buffer to a single flat buffer.  */
+    alts_grpc_record_protocol_copy_slice_buffer(
+        protected_slices, integrity_only_record_protocol->tag_buf);
+    tag_iovec.iov_base = integrity_only_record_protocol->tag_buf;
+  }
+  /* Calls alts_iovec_record_protocol unprotect.  */
+  char* error_details = nullptr;
+  alts_grpc_record_protocol_convert_slice_buffer_to_iovec(
+      rp, &integrity_only_record_protocol->data_sb);
+  grpc_status_code status = alts_iovec_record_protocol_integrity_only_unprotect(
+      rp->iovec_rp, rp->iovec_buf,
+      integrity_only_record_protocol->data_sb.count, header_iovec, tag_iovec,
+      &error_details);
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "Failed to unprotect, %s", error_details);
+    gpr_free(error_details);
+    return TSI_INTERNAL_ERROR;
+  }
+  grpc_slice_buffer_reset_and_unref_internal(&rp->header_sb);
+  grpc_slice_buffer_reset_and_unref_internal(protected_slices);
+  grpc_slice_buffer_move_into(&integrity_only_record_protocol->data_sb,
+                              unprotected_slices);
+  return TSI_OK;
+}
+
+static void alts_grpc_integrity_only_destruct(alts_grpc_record_protocol* rp) {
+  if (rp == nullptr) {
+    return;
+  }
+  alts_grpc_integrity_only_record_protocol* integrity_only_rp =
+      reinterpret_cast<alts_grpc_integrity_only_record_protocol*>(rp);
+  grpc_slice_buffer_destroy_internal(&integrity_only_rp->data_sb);
+  gpr_free(integrity_only_rp->tag_buf);
+}
+
+static const alts_grpc_record_protocol_vtable
+    alts_grpc_integrity_only_record_protocol_vtable = {
+        alts_grpc_integrity_only_protect, alts_grpc_integrity_only_unprotect,
+        alts_grpc_integrity_only_destruct};
+
+tsi_result alts_grpc_integrity_only_record_protocol_create(
+    gsec_aead_crypter* crypter, size_t overflow_size, bool is_client,
+    bool is_protect, alts_grpc_record_protocol** rp) {
+  if (crypter == nullptr || rp == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to alts_grpc_record_protocol create.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_grpc_integrity_only_record_protocol* impl =
+      static_cast<alts_grpc_integrity_only_record_protocol*>(
+          gpr_zalloc(sizeof(alts_grpc_integrity_only_record_protocol)));
+  /* Calls alts_grpc_record_protocol init.  */
+  tsi_result result = alts_grpc_record_protocol_init(
+      &impl->base, crypter, overflow_size, is_client,
+      /*is_integrity_only=*/true, is_protect);
+  if (result != TSI_OK) {
+    gpr_free(impl);
+    return result;
+  }
+  /* Initializes slice buffer for data_sb.  */
+  grpc_slice_buffer_init(&impl->data_sb);
+  /* Allocates tag buffer.  */
+  impl->tag_buf =
+      static_cast<unsigned char*>(gpr_malloc(impl->base.tag_length));
+  impl->base.vtable = &alts_grpc_integrity_only_record_protocol_vtable;
+  *rp = &impl->base;
+  return TSI_OK;
+}
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.h b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.h
new file mode 100644
index 0000000000..8d68b27e07
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.h
@@ -0,0 +1,52 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_INTEGRITY_ONLY_RECORD_PROTOCOL_H
+#define GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_INTEGRITY_ONLY_RECORD_PROTOCOL_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stdbool.h>
+
+#include "src/core/tsi/alts/crypt/gsec.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol.h"
+
+/**
+ * This method creates an integrity-only alts_grpc_record_protocol instance,
+ * given a gsec_aead_crypter instance and a flag indicating if the created
+ * instance will be used at the client or server side. The ownership of
+ * gsec_aead_crypter instance is transferred to this new object.
+ *
+ * - crypter: a gsec_aead_crypter instance used to perform AEAD decryption.
+ * - overflow_size: overflow size of counter in bytes.
+ * - is_client: a flag indicating if the alts_grpc_record_protocol instance will
+ *   be used at the client or server side.
+ * - is_protect: a flag indicating if the alts_grpc_record_protocol instance
+ *   will be used for protect or unprotect.
+ * - rp: an alts_grpc_record_protocol instance to be returned from
+ *   the method.
+ *
+ * This method returns TSI_OK in case of success or a specific error code in
+ * case of failure.
+ */
+tsi_result alts_grpc_integrity_only_record_protocol_create(
+    gsec_aead_crypter* crypter, size_t overflow_size, bool is_client,
+    bool is_protect, alts_grpc_record_protocol** rp);
+
+#endif /* GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_INTEGRITY_ONLY_RECORD_PROTOCOL_H \
+        */
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_privacy_integrity_record_protocol.cc b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_privacy_integrity_record_protocol.cc
new file mode 100644
index 0000000000..d4fd88d1e2
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_privacy_integrity_record_protocol.cc
@@ -0,0 +1,144 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_privacy_integrity_record_protocol.h"
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/lib/slice/slice_internal.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.h"
+
+/* Privacy-integrity alts_grpc_record_protocol object uses the same struct
+ * defined in alts_grpc_record_protocol_common.h.  */
+
+/* --- alts_grpc_record_protocol methods implementation. --- */
+
+static tsi_result alts_grpc_privacy_integrity_protect(
+    alts_grpc_record_protocol* rp, grpc_slice_buffer* unprotected_slices,
+    grpc_slice_buffer* protected_slices) {
+  /* Input sanity check.  */
+  if (rp == nullptr || unprotected_slices == nullptr ||
+      protected_slices == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to alts_grpc_record_protocol protect.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  /* Allocates memory for output frame. In privacy-integrity protect, the
+   * protected frame is stored in a newly allocated buffer.  */
+  size_t protected_frame_size =
+      unprotected_slices->length + rp->header_length +
+      alts_iovec_record_protocol_get_tag_length(rp->iovec_rp);
+  grpc_slice protected_slice = GRPC_SLICE_MALLOC(protected_frame_size);
+  iovec_t protected_iovec = {GRPC_SLICE_START_PTR(protected_slice),
+                             GRPC_SLICE_LENGTH(protected_slice)};
+  /* Calls alts_iovec_record_protocol protect.  */
+  char* error_details = nullptr;
+  alts_grpc_record_protocol_convert_slice_buffer_to_iovec(rp,
+                                                          unprotected_slices);
+  grpc_status_code status =
+      alts_iovec_record_protocol_privacy_integrity_protect(
+          rp->iovec_rp, rp->iovec_buf, unprotected_slices->count,
+          protected_iovec, &error_details);
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "Failed to protect, %s", error_details);
+    gpr_free(error_details);
+    grpc_slice_unref(protected_slice);
+    return TSI_INTERNAL_ERROR;
+  }
+  grpc_slice_buffer_add(protected_slices, protected_slice);
+  grpc_slice_buffer_reset_and_unref_internal(unprotected_slices);
+  return TSI_OK;
+}
+
+static tsi_result alts_grpc_privacy_integrity_unprotect(
+    alts_grpc_record_protocol* rp, grpc_slice_buffer* protected_slices,
+    grpc_slice_buffer* unprotected_slices) {
+  /* Input sanity check.  */
+  if (rp == nullptr || protected_slices == nullptr ||
+      unprotected_slices == nullptr) {
+    gpr_log(
+        GPR_ERROR,
+        "Invalid nullptr arguments to alts_grpc_record_protocol unprotect.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  /* Allocates memory for output frame. In privacy-integrity unprotect, the
+   * unprotected data are stored in a newly allocated buffer.  */
+  if (protected_slices->length < rp->header_length + rp->tag_length) {
+    gpr_log(GPR_ERROR, "Protected slices do not have sufficient data.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  size_t unprotected_frame_size =
+      protected_slices->length - rp->header_length - rp->tag_length;
+  grpc_slice unprotected_slice = GRPC_SLICE_MALLOC(unprotected_frame_size);
+  iovec_t unprotected_iovec = {GRPC_SLICE_START_PTR(unprotected_slice),
+                               GRPC_SLICE_LENGTH(unprotected_slice)};
+  /* Strips frame header from protected slices.  */
+  grpc_slice_buffer_reset_and_unref_internal(&rp->header_sb);
+  grpc_slice_buffer_move_first(protected_slices, rp->header_length,
+                               &rp->header_sb);
+  iovec_t header_iovec = alts_grpc_record_protocol_get_header_iovec(rp);
+  /* Calls alts_iovec_record_protocol unprotect.  */
+  char* error_details = nullptr;
+  alts_grpc_record_protocol_convert_slice_buffer_to_iovec(rp, protected_slices);
+  grpc_status_code status =
+      alts_iovec_record_protocol_privacy_integrity_unprotect(
+          rp->iovec_rp, header_iovec, rp->iovec_buf, protected_slices->count,
+          unprotected_iovec, &error_details);
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "Failed to unprotect, %s", error_details);
+    gpr_free(error_details);
+    grpc_slice_unref(unprotected_slice);
+    return TSI_INTERNAL_ERROR;
+  }
+  grpc_slice_buffer_reset_and_unref_internal(&rp->header_sb);
+  grpc_slice_buffer_reset_and_unref_internal(protected_slices);
+  grpc_slice_buffer_add(unprotected_slices, unprotected_slice);
+  return TSI_OK;
+}
+
+static const alts_grpc_record_protocol_vtable
+    alts_grpc_privacy_integrity_record_protocol_vtable = {
+        alts_grpc_privacy_integrity_protect,
+        alts_grpc_privacy_integrity_unprotect, nullptr};
+
+tsi_result alts_grpc_privacy_integrity_record_protocol_create(
+    gsec_aead_crypter* crypter, size_t overflow_size, bool is_client,
+    bool is_protect, alts_grpc_record_protocol** rp) {
+  if (crypter == nullptr || rp == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to alts_grpc_record_protocol create.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  auto* impl = static_cast<alts_grpc_record_protocol*>(
+      gpr_zalloc(sizeof(alts_grpc_record_protocol)));
+  /* Calls alts_grpc_record_protocol init.  */
+  tsi_result result =
+      alts_grpc_record_protocol_init(impl, crypter, overflow_size, is_client,
+                                     /*is_integrity_only=*/false, is_protect);
+  if (result != TSI_OK) {
+    gpr_free(impl);
+    return result;
+  }
+  impl->vtable = &alts_grpc_privacy_integrity_record_protocol_vtable;
+  *rp = impl;
+  return TSI_OK;
+}
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_privacy_integrity_record_protocol.h b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_privacy_integrity_record_protocol.h
new file mode 100644
index 0000000000..1e34aef2d8
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_privacy_integrity_record_protocol.h
@@ -0,0 +1,49 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_PRIVACY_INTEGRITY_RECORD_PROTOCOL_H
+#define GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_PRIVACY_INTEGRITY_RECORD_PROTOCOL_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stdbool.h>
+
+#include "src/core/tsi/alts/crypt/gsec.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol.h"
+
+/**
+ * This method creates a privacy-integrity alts_grpc_record_protocol instance,
+ * given a gsec_aead_crypter instance and a flag indicating if the created
+ * instance will be used at the client or server side. The ownership of
+ * gsec_aead_crypter instance is transferred to this new object.
+ *
+ * - crypter: a gsec_aead_crypter instance used to perform AEAD decryption.
+ * - is_client: a flag indicating if the alts_grpc_record_protocol instance will
+ *   be used at the client or server side.
+ * - rp: an alts_grpc_record_protocol instance to be returned from
+ *   the method.
+ *
+ * This method returns TSI_OK in case of success or a specific error code in
+ * case of failure.
+ */
+tsi_result alts_grpc_privacy_integrity_record_protocol_create(
+    gsec_aead_crypter* crypter, size_t overflow_size, bool is_client,
+    bool is_protect, alts_grpc_record_protocol** rp);
+
+#endif /* GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_PRIVACY_INTEGRITY_RECORD_PROTOCOL_H \
+        */
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol.h b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol.h
new file mode 100644
index 0000000000..d1e433dac4
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol.h
@@ -0,0 +1,91 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_RECORD_PROTOCOL_H
+#define GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_RECORD_PROTOCOL_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/slice_buffer.h>
+
+#include "src/core/tsi/transport_security_interface.h"
+
+/**
+ * This alts_grpc_record_protocol object protects and unprotects a single frame
+ * stored in grpc slice buffer with zero or minimized memory copy.
+ * Implementations of this object must be thread compatible.
+ */
+typedef struct alts_grpc_record_protocol alts_grpc_record_protocol;
+
+/**
+ * This methods performs protect operation on unprotected data and appends the
+ * protected frame to protected_slices. The caller needs to ensure the length
+ * of unprotected data plus the frame overhead is less than or equal to the
+ * maximum frame length. The input unprotected data slice buffer will be
+ * cleared, although the actual unprotected data bytes are not modified.
+ *
+ * - self: an alts_grpc_record_protocol instance.
+ * - unprotected_slices: the unprotected data to be protected.
+ * - protected_slices: slice buffer where the protected frame is appended.
+ *
+ * This method returns TSI_OK in case of success or a specific error code in
+ * case of failure.
+ */
+tsi_result alts_grpc_record_protocol_protect(
+    alts_grpc_record_protocol* self, grpc_slice_buffer* unprotected_slices,
+    grpc_slice_buffer* protected_slices);
+
+/**
+ * This methods performs unprotect operation on a full frame of protected data
+ * and appends unprotected data to unprotected_slices. It is the caller's
+ * responsibility to prepare a full frame of data before calling this method.
+ * The input protected frame slice buffer will be cleared, although the actual
+ * protected data bytes are not modified.
+ *
+ * - self: an alts_grpc_record_protocol instance.
+ * - protected_slices: a full frame of protected data in grpc slices.
+ * - unprotected_slices: slice buffer where unprotected data is appended.
+ *
+ * This method returns TSI_OK in case of success or a specific error code in
+ * case of failure.
+ */
+tsi_result alts_grpc_record_protocol_unprotect(
+    alts_grpc_record_protocol* self, grpc_slice_buffer* protected_slices,
+    grpc_slice_buffer* unprotected_slices);
+
+/**
+ * This method returns maximum allowed unprotected data size, given maximum
+ * protected frame size.
+ *
+ * - self: an alts_grpc_record_protocol instance.
+ * - max_protected_frame_size: maximum protected frame size.
+ *
+ * On success, the method returns the maximum allowed unprotected data size.
+ * Otherwise, it returns zero.
+ */
+size_t alts_grpc_record_protocol_max_unprotected_data_size(
+    const alts_grpc_record_protocol* self, size_t max_protected_frame_size);
+
+/**
+ * This method destroys an alts_grpc_record_protocol instance by de-allocating
+ * all of its occupied memory.
+ */
+void alts_grpc_record_protocol_destroy(alts_grpc_record_protocol* self);
+
+#endif /* GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_RECORD_PROTOCOL_H \
+        */
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.cc b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.cc
new file mode 100644
index 0000000000..ff91aea350
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.cc
@@ -0,0 +1,173 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/lib/gpr/useful.h"
+#include "src/core/lib/slice/slice_internal.h"
+
+const size_t kInitialIovecBufferSize = 8;
+
+/* Makes sure iovec_buf in alts_grpc_record_protocol is large enough.  */
+static void ensure_iovec_buf_size(alts_grpc_record_protocol* rp,
+                                  const grpc_slice_buffer* sb) {
+  GPR_ASSERT(rp != nullptr && sb != nullptr);
+  if (sb->count <= rp->iovec_buf_length) {
+    return;
+  }
+  /* At least double the iovec buffer size.  */
+  rp->iovec_buf_length = GPR_MAX(sb->count, 2 * rp->iovec_buf_length);
+  rp->iovec_buf = static_cast<iovec_t*>(
+      gpr_realloc(rp->iovec_buf, rp->iovec_buf_length * sizeof(iovec_t)));
+}
+
+/* --- Implementation of methods defined in tsi_grpc_record_protocol_common.h.
+ * --- */
+
+void alts_grpc_record_protocol_convert_slice_buffer_to_iovec(
+    alts_grpc_record_protocol* rp, const grpc_slice_buffer* sb) {
+  GPR_ASSERT(rp != nullptr && sb != nullptr);
+  ensure_iovec_buf_size(rp, sb);
+  for (size_t i = 0; i < sb->count; i++) {
+    rp->iovec_buf[i].iov_base = GRPC_SLICE_START_PTR(sb->slices[i]);
+    rp->iovec_buf[i].iov_len = GRPC_SLICE_LENGTH(sb->slices[i]);
+  }
+}
+
+void alts_grpc_record_protocol_copy_slice_buffer(const grpc_slice_buffer* src,
+                                                 unsigned char* dst) {
+  GPR_ASSERT(src != nullptr && dst != nullptr);
+  for (size_t i = 0; i < src->count; i++) {
+    size_t slice_length = GRPC_SLICE_LENGTH(src->slices[i]);
+    memcpy(dst, GRPC_SLICE_START_PTR(src->slices[i]), slice_length);
+    dst += slice_length;
+  }
+}
+
+iovec_t alts_grpc_record_protocol_get_header_iovec(
+    alts_grpc_record_protocol* rp) {
+  iovec_t header_iovec = {nullptr, 0};
+  if (rp == nullptr) {
+    return header_iovec;
+  }
+  header_iovec.iov_len = rp->header_length;
+  if (rp->header_sb.count == 1) {
+    header_iovec.iov_base = GRPC_SLICE_START_PTR(rp->header_sb.slices[0]);
+  } else {
+    /* Frame header is in multiple slices, copies the header bytes from slice
+     * buffer to a single flat buffer.  */
+    alts_grpc_record_protocol_copy_slice_buffer(&rp->header_sb, rp->header_buf);
+    header_iovec.iov_base = rp->header_buf;
+  }
+  return header_iovec;
+}
+
+tsi_result alts_grpc_record_protocol_init(alts_grpc_record_protocol* rp,
+                                          gsec_aead_crypter* crypter,
+                                          size_t overflow_size, bool is_client,
+                                          bool is_integrity_only,
+                                          bool is_protect) {
+  if (rp == nullptr || crypter == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to alts_grpc_record_protocol init.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  /* Creates alts_iovec_record_protocol.  */
+  char* error_details = nullptr;
+  grpc_status_code status = alts_iovec_record_protocol_create(
+      crypter, overflow_size, is_client, is_integrity_only, is_protect,
+      &rp->iovec_rp, &error_details);
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "Failed to create alts_iovec_record_protocol, %s.",
+            error_details);
+    gpr_free(error_details);
+    return TSI_INTERNAL_ERROR;
+  }
+  /* Allocates header slice buffer.  */
+  grpc_slice_buffer_init(&rp->header_sb);
+  /* Allocates header buffer.  */
+  rp->header_length = alts_iovec_record_protocol_get_header_length();
+  rp->header_buf = static_cast<unsigned char*>(gpr_malloc(rp->header_length));
+  rp->tag_length = alts_iovec_record_protocol_get_tag_length(rp->iovec_rp);
+  /* Allocates iovec buffer.  */
+  rp->iovec_buf_length = kInitialIovecBufferSize;
+  rp->iovec_buf =
+      static_cast<iovec_t*>(gpr_malloc(rp->iovec_buf_length * sizeof(iovec_t)));
+  return TSI_OK;
+}
+
+/* --- Implementation of methods defined in tsi_grpc_record_protocol.h. --- */
+tsi_result alts_grpc_record_protocol_protect(
+    alts_grpc_record_protocol* self, grpc_slice_buffer* unprotected_slices,
+    grpc_slice_buffer* protected_slices) {
+  if (grpc_core::ExecCtx::Get() == nullptr || self == nullptr ||
+      self->vtable == nullptr || unprotected_slices == nullptr ||
+      protected_slices == nullptr) {
+    return TSI_INVALID_ARGUMENT;
+  }
+  if (self->vtable->protect == nullptr) {
+    return TSI_UNIMPLEMENTED;
+  }
+  return self->vtable->protect(self, unprotected_slices, protected_slices);
+}
+
+tsi_result alts_grpc_record_protocol_unprotect(
+    alts_grpc_record_protocol* self, grpc_slice_buffer* protected_slices,
+    grpc_slice_buffer* unprotected_slices) {
+  if (grpc_core::ExecCtx::Get() == nullptr || self == nullptr ||
+      self->vtable == nullptr || protected_slices == nullptr ||
+      unprotected_slices == nullptr) {
+    return TSI_INVALID_ARGUMENT;
+  }
+  if (self->vtable->unprotect == nullptr) {
+    return TSI_UNIMPLEMENTED;
+  }
+  return self->vtable->unprotect(self, protected_slices, unprotected_slices);
+}
+
+void alts_grpc_record_protocol_destroy(alts_grpc_record_protocol* self) {
+  if (self == nullptr) {
+    return;
+  }
+  if (self->vtable->destruct != nullptr) {
+    self->vtable->destruct(self);
+  }
+  alts_iovec_record_protocol_destroy(self->iovec_rp);
+  grpc_slice_buffer_destroy_internal(&self->header_sb);
+  gpr_free(self->header_buf);
+  gpr_free(self->iovec_buf);
+  gpr_free(self);
+}
+
+/* Integrity-only and privacy-integrity share the same implementation. No need
+ * to call vtable.  */
+size_t alts_grpc_record_protocol_max_unprotected_data_size(
+    const alts_grpc_record_protocol* self, size_t max_protected_frame_size) {
+  if (self == nullptr) {
+    return 0;
+  }
+  return alts_iovec_record_protocol_max_unprotected_data_size(
+      self->iovec_rp, max_protected_frame_size);
+}
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.h b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.h
new file mode 100644
index 0000000000..43b8a4a2b8
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol_common.h
@@ -0,0 +1,100 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_RECORD_PROTOCOL_COMMON_H
+#define GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_RECORD_PROTOCOL_COMMON_H
+
+/**
+ * this file contains alts_grpc_record_protocol internals and internal-only
+ * helper functions. The public functions of alts_grpc_record_protocol are
+ * defined in the alts_grpc_record_protocol.h.
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.h"
+
+/* V-table for alts_grpc_record_protocol implementations.  */
+typedef struct {
+  tsi_result (*protect)(alts_grpc_record_protocol* self,
+                        grpc_slice_buffer* unprotected_slices,
+                        grpc_slice_buffer* protected_slices);
+  tsi_result (*unprotect)(alts_grpc_record_protocol* self,
+                          grpc_slice_buffer* protected_slices,
+                          grpc_slice_buffer* unprotected_slices);
+  void (*destruct)(alts_grpc_record_protocol* self);
+} alts_grpc_record_protocol_vtable;
+
+/* Main struct for alts_grpc_record_protocol implementation, shared by both
+ * integrity-only record protocol and privacy-integrity record protocol.
+ * Integrity-only record protocol has additional data elements.
+ * Privacy-integrity record protocol uses this struct directly.  */
+struct alts_grpc_record_protocol {
+  const alts_grpc_record_protocol_vtable* vtable;
+  alts_iovec_record_protocol* iovec_rp;
+  grpc_slice_buffer header_sb;
+  unsigned char* header_buf;
+  size_t header_length;
+  size_t tag_length;
+  iovec_t* iovec_buf;
+  size_t iovec_buf_length;
+};
+
+/**
+ * Converts the slices of input sb into iovec_t's and puts the result into
+ * rp->iovec_buf. Note that the actual data are not copied, only
+ * pointers and lengths are copied.
+ */
+void alts_grpc_record_protocol_convert_slice_buffer_to_iovec(
+    alts_grpc_record_protocol* rp, const grpc_slice_buffer* sb);
+
+/**
+ * Copies bytes from slice buffer to destination buffer. Caller is responsible
+ * for allocating enough memory of destination buffer. This method is used for
+ * copying frame header and tag in case they are stored in multiple slices.
+ */
+void alts_grpc_record_protocol_copy_slice_buffer(const grpc_slice_buffer* src,
+                                                 unsigned char* dst);
+
+/**
+ * This method returns an iovec object pointing to the frame header stored in
+ * rp->header_sb. If the frame header is stored in multiple slices,
+ * this method will copy the bytes in rp->header_sb to
+ * rp->header_buf, and return an iovec object pointing to
+ * rp->header_buf.
+ */
+iovec_t alts_grpc_record_protocol_get_header_iovec(
+    alts_grpc_record_protocol* rp);
+
+/**
+ * Initializes an alts_grpc_record_protocol object, given a gsec_aead_crypter
+ * instance, the overflow size of the counter in bytes, a flag indicating if the
+ * object is used for client or server side, a flag indicating if it is used for
+ * integrity-only or privacy-integrity mode, and a flag indicating if it is for
+ * protect or unprotect. The ownership of gsec_aead_crypter object is
+ * transferred to the alts_grpc_record_protocol object.
+ */
+tsi_result alts_grpc_record_protocol_init(alts_grpc_record_protocol* rp,
+                                          gsec_aead_crypter* crypter,
+                                          size_t overflow_size, bool is_client,
+                                          bool is_integrity_only,
+                                          bool is_protect);
+
+#endif /* GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_GRPC_RECORD_PROTOCOL_COMMON_H \
+        */
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.cc b/src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.cc
new file mode 100644
index 0000000000..6a548e50dd
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.cc
@@ -0,0 +1,476 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/tsi/alts/frame_protector/alts_counter.h"
+
+struct alts_iovec_record_protocol {
+  alts_counter* ctr;
+  gsec_aead_crypter* crypter;
+  size_t tag_length;
+  bool is_integrity_only;
+  bool is_protect;
+};
+
+/* Copies error message to destination.  */
+static void maybe_copy_error_msg(const char* src, char** dst) {
+  if (dst != nullptr && src != nullptr) {
+    *dst = static_cast<char*>(gpr_malloc(strlen(src) + 1));
+    memcpy(*dst, src, strlen(src) + 1);
+  }
+}
+
+/* Appends error message to destination.  */
+static void maybe_append_error_msg(const char* appendix, char** dst) {
+  if (dst != nullptr && appendix != nullptr) {
+    int dst_len = static_cast<int>(strlen(*dst));
+    *dst = static_cast<char*>(realloc(*dst, dst_len + strlen(appendix) + 1));
+    assert(*dst != nullptr);
+    memcpy(*dst + dst_len, appendix, strlen(appendix) + 1);
+  }
+}
+
+/* Use little endian to interpret a string of bytes as uint32_t.  */
+static uint32_t load_32_le(const unsigned char* buffer) {
+  return (((uint32_t)buffer[3]) << 24) | (((uint32_t)buffer[2]) << 16) |
+         (((uint32_t)buffer[1]) << 8) | ((uint32_t)buffer[0]);
+}
+
+/* Store uint32_t as a string of little endian bytes.  */
+static void store_32_le(uint32_t value, unsigned char* buffer) {
+  buffer[3] = (unsigned char)(value >> 24) & 0xFF;
+  buffer[2] = (unsigned char)(value >> 16) & 0xFF;
+  buffer[1] = (unsigned char)(value >> 8) & 0xFF;
+  buffer[0] = (unsigned char)(value)&0xFF;
+}
+
+/* Ensures header and tag iovec have sufficient length.  */
+static grpc_status_code ensure_header_and_tag_length(
+    const alts_iovec_record_protocol* rp, iovec_t header, iovec_t tag,
+    char** error_details) {
+  if (rp == nullptr) {
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  if (header.iov_base == nullptr) {
+    maybe_copy_error_msg("Header is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (header.iov_len != alts_iovec_record_protocol_get_header_length()) {
+    maybe_copy_error_msg("Header length is incorrect.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (tag.iov_base == nullptr) {
+    maybe_copy_error_msg("Tag is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (tag.iov_len != rp->tag_length) {
+    maybe_copy_error_msg("Tag length is incorrect.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  return GRPC_STATUS_OK;
+}
+
+/* Increments crypter counter and checks overflow.  */
+static grpc_status_code increment_counter(alts_counter* counter,
+                                          char** error_details) {
+  if (counter == nullptr) {
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  bool is_overflow = false;
+  grpc_status_code status =
+      alts_counter_increment(counter, &is_overflow, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  if (is_overflow) {
+    maybe_copy_error_msg("Crypter counter is overflowed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  return GRPC_STATUS_OK;
+}
+
+/* Given an array of iovec, computes the total length of buffer.  */
+static size_t get_total_length(const iovec_t* vec, size_t vec_length) {
+  size_t total_length = 0;
+  for (size_t i = 0; i < vec_length; ++i) {
+    total_length += vec[i].iov_len;
+  }
+  return total_length;
+}
+
+/* Writes frame header given data and tag length.  */
+static grpc_status_code write_frame_header(size_t data_length,
+                                           unsigned char* header,
+                                           char** error_details) {
+  if (header == nullptr) {
+    maybe_copy_error_msg("Header is nullptr.", error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  size_t frame_length = kZeroCopyFrameMessageTypeFieldSize + data_length;
+  store_32_le(static_cast<uint32_t>(frame_length), header);
+  store_32_le(kZeroCopyFrameMessageType,
+              header + kZeroCopyFrameLengthFieldSize);
+  return GRPC_STATUS_OK;
+}
+
+/* Verifies frame header given protected data length.  */
+static grpc_status_code verify_frame_header(size_t data_length,
+                                            unsigned char* header,
+                                            char** error_details) {
+  if (header == nullptr) {
+    maybe_copy_error_msg("Header is nullptr.", error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  size_t frame_length = load_32_le(header);
+  if (frame_length != kZeroCopyFrameMessageTypeFieldSize + data_length) {
+    maybe_copy_error_msg("Bad frame length.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  size_t message_type = load_32_le(header + kZeroCopyFrameLengthFieldSize);
+  if (message_type != kZeroCopyFrameMessageType) {
+    maybe_copy_error_msg("Unsupported message type.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  return GRPC_STATUS_OK;
+}
+
+/* --- alts_iovec_record_protocol methods implementation. --- */
+
+size_t alts_iovec_record_protocol_get_header_length() {
+  return kZeroCopyFrameHeaderSize;
+}
+
+size_t alts_iovec_record_protocol_get_tag_length(
+    const alts_iovec_record_protocol* rp) {
+  if (rp != nullptr) {
+    return rp->tag_length;
+  }
+  return 0;
+}
+
+size_t alts_iovec_record_protocol_max_unprotected_data_size(
+    const alts_iovec_record_protocol* rp, size_t max_protected_frame_size) {
+  if (rp == nullptr) {
+    return 0;
+  }
+  size_t overhead_bytes_size =
+      kZeroCopyFrameMessageTypeFieldSize + rp->tag_length;
+  if (max_protected_frame_size <= overhead_bytes_size) return 0;
+  return max_protected_frame_size - overhead_bytes_size;
+}
+
+grpc_status_code alts_iovec_record_protocol_integrity_only_protect(
+    alts_iovec_record_protocol* rp, const iovec_t* unprotected_vec,
+    size_t unprotected_vec_length, iovec_t header, iovec_t tag,
+    char** error_details) {
+  /* Input sanity checks.  */
+  if (rp == nullptr) {
+    maybe_copy_error_msg("Input iovec_record_protocol is nullptr.",
+                         error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (!rp->is_integrity_only) {
+    maybe_copy_error_msg(
+        "Integrity-only operations are not allowed for this object.",
+        error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  if (!rp->is_protect) {
+    maybe_copy_error_msg("Protect operations are not allowed for this object.",
+                         error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  grpc_status_code status =
+      ensure_header_and_tag_length(rp, header, tag, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Unprotected data should not be zero length.  */
+  size_t data_length =
+      get_total_length(unprotected_vec, unprotected_vec_length);
+  /* Sets frame header.  */
+  status = write_frame_header(data_length + rp->tag_length,
+                              static_cast<unsigned char*>(header.iov_base),
+                              error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Computes frame tag by calling AEAD crypter.  */
+  size_t bytes_written = 0;
+  status = gsec_aead_crypter_encrypt_iovec(
+      rp->crypter, alts_counter_get_counter(rp->ctr),
+      alts_counter_get_size(rp->ctr), unprotected_vec, unprotected_vec_length,
+      /* plaintext_vec = */ nullptr, /* plaintext_vec_length = */ 0, tag,
+      &bytes_written, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  if (bytes_written != rp->tag_length) {
+    maybe_copy_error_msg("Bytes written expects to be the same as tag length.",
+                         error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  /* Increments the crypter counter.  */
+  return increment_counter(rp->ctr, error_details);
+}
+
+grpc_status_code alts_iovec_record_protocol_integrity_only_unprotect(
+    alts_iovec_record_protocol* rp, const iovec_t* protected_vec,
+    size_t protected_vec_length, iovec_t header, iovec_t tag,
+    char** error_details) {
+  /* Input sanity checks.  */
+  if (rp == nullptr) {
+    maybe_copy_error_msg("Input iovec_record_protocol is nullptr.",
+                         error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (!rp->is_integrity_only) {
+    maybe_copy_error_msg(
+        "Integrity-only operations are not allowed for this object.",
+        error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  if (rp->is_protect) {
+    maybe_copy_error_msg(
+        "Unprotect operations are not allowed for this object.", error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  grpc_status_code status =
+      ensure_header_and_tag_length(rp, header, tag, error_details);
+  if (status != GRPC_STATUS_OK) return status;
+  /* Protected data should not be zero length.  */
+  size_t data_length = get_total_length(protected_vec, protected_vec_length);
+  /* Verifies frame header.  */
+  status = verify_frame_header(data_length + rp->tag_length,
+                               static_cast<unsigned char*>(header.iov_base),
+                               error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Verifies frame tag by calling AEAD crypter.  */
+  iovec_t plaintext = {nullptr, 0};
+  size_t bytes_written = 0;
+  status = gsec_aead_crypter_decrypt_iovec(
+      rp->crypter, alts_counter_get_counter(rp->ctr),
+      alts_counter_get_size(rp->ctr), protected_vec, protected_vec_length, &tag,
+      1, plaintext, &bytes_written, error_details);
+  if (status != GRPC_STATUS_OK || bytes_written != 0) {
+    maybe_append_error_msg(" Frame tag verification failed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  /* Increments the crypter counter.  */
+  return increment_counter(rp->ctr, error_details);
+}
+
+grpc_status_code alts_iovec_record_protocol_privacy_integrity_protect(
+    alts_iovec_record_protocol* rp, const iovec_t* unprotected_vec,
+    size_t unprotected_vec_length, iovec_t protected_frame,
+    char** error_details) {
+  /* Input sanity checks.  */
+  if (rp == nullptr) {
+    maybe_copy_error_msg("Input iovec_record_protocol is nullptr.",
+                         error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (rp->is_integrity_only) {
+    maybe_copy_error_msg(
+        "Privacy-integrity operations are not allowed for this object.",
+        error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  if (!rp->is_protect) {
+    maybe_copy_error_msg("Protect operations are not allowed for this object.",
+                         error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  /* Unprotected data should not be zero length.  */
+  size_t data_length =
+      get_total_length(unprotected_vec, unprotected_vec_length);
+  /* Ensures protected frame iovec has sufficient size.  */
+  if (protected_frame.iov_base == nullptr) {
+    maybe_copy_error_msg("Protected frame is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (protected_frame.iov_len !=
+      alts_iovec_record_protocol_get_header_length() + data_length +
+          rp->tag_length) {
+    maybe_copy_error_msg("Protected frame size is incorrect.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  /* Writer frame header.  */
+  grpc_status_code status = write_frame_header(
+      data_length + rp->tag_length,
+      static_cast<unsigned char*>(protected_frame.iov_base), error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Encrypt unprotected data by calling AEAD crypter.  */
+  unsigned char* ciphertext_buffer =
+      static_cast<unsigned char*>(protected_frame.iov_base) +
+      alts_iovec_record_protocol_get_header_length();
+  iovec_t ciphertext = {ciphertext_buffer, data_length + rp->tag_length};
+  size_t bytes_written = 0;
+  status = gsec_aead_crypter_encrypt_iovec(
+      rp->crypter, alts_counter_get_counter(rp->ctr),
+      alts_counter_get_size(rp->ctr), /* aad_vec = */ nullptr,
+      /* aad_vec_length = */ 0, unprotected_vec, unprotected_vec_length,
+      ciphertext, &bytes_written, error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  if (bytes_written != data_length + rp->tag_length) {
+    maybe_copy_error_msg(
+        "Bytes written expects to be data length plus tag length.",
+        error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  /* Increments the crypter counter. */
+  return increment_counter(rp->ctr, error_details);
+}
+
+grpc_status_code alts_iovec_record_protocol_privacy_integrity_unprotect(
+    alts_iovec_record_protocol* rp, iovec_t header,
+    const iovec_t* protected_vec, size_t protected_vec_length,
+    iovec_t unprotected_data, char** error_details) {
+  /* Input sanity checks.  */
+  if (rp == nullptr) {
+    maybe_copy_error_msg("Input iovec_record_protocol is nullptr.",
+                         error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (rp->is_integrity_only) {
+    maybe_copy_error_msg(
+        "Privacy-integrity operations are not allowed for this object.",
+        error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  if (rp->is_protect) {
+    maybe_copy_error_msg(
+        "Unprotect operations are not allowed for this object.", error_details);
+    return GRPC_STATUS_FAILED_PRECONDITION;
+  }
+  /* Protected data size should be no less than tag size.  */
+  size_t protected_data_length =
+      get_total_length(protected_vec, protected_vec_length);
+  if (protected_data_length < rp->tag_length) {
+    maybe_copy_error_msg(
+        "Protected data length should be more than the tag length.",
+        error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  /* Ensures header has sufficient size.  */
+  if (header.iov_base == nullptr) {
+    maybe_copy_error_msg("Header is nullptr.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  if (header.iov_len != alts_iovec_record_protocol_get_header_length()) {
+    maybe_copy_error_msg("Header length is incorrect.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  /* Ensures unprotected data iovec has sufficient size.  */
+  if (unprotected_data.iov_len != protected_data_length - rp->tag_length) {
+    maybe_copy_error_msg("Unprotected data size is incorrect.", error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  /* Verify frame header.  */
+  grpc_status_code status = verify_frame_header(
+      protected_data_length, static_cast<unsigned char*>(header.iov_base),
+      error_details);
+  if (status != GRPC_STATUS_OK) {
+    return status;
+  }
+  /* Decrypt protected data by calling AEAD crypter.  */
+  size_t bytes_written = 0;
+  status = gsec_aead_crypter_decrypt_iovec(
+      rp->crypter, alts_counter_get_counter(rp->ctr),
+      alts_counter_get_size(rp->ctr), /* aad_vec = */ nullptr,
+      /* aad_vec_length = */ 0, protected_vec, protected_vec_length,
+      unprotected_data, &bytes_written, error_details);
+  if (status != GRPC_STATUS_OK) {
+    maybe_append_error_msg(" Frame decryption failed.", error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  if (bytes_written != protected_data_length - rp->tag_length) {
+    maybe_copy_error_msg(
+        "Bytes written expects to be protected data length minus tag length.",
+        error_details);
+    return GRPC_STATUS_INTERNAL;
+  }
+  /* Increments the crypter counter. */
+  return increment_counter(rp->ctr, error_details);
+}
+
+grpc_status_code alts_iovec_record_protocol_create(
+    gsec_aead_crypter* crypter, size_t overflow_size, bool is_client,
+    bool is_integrity_only, bool is_protect, alts_iovec_record_protocol** rp,
+    char** error_details) {
+  if (crypter == nullptr || rp == nullptr) {
+    maybe_copy_error_msg(
+        "Invalid nullptr arguments to alts_iovec_record_protocol create.",
+        error_details);
+    return GRPC_STATUS_INVALID_ARGUMENT;
+  }
+  alts_iovec_record_protocol* impl = static_cast<alts_iovec_record_protocol*>(
+      gpr_zalloc(sizeof(alts_iovec_record_protocol)));
+  /* Gets counter length.  */
+  size_t counter_length = 0;
+  grpc_status_code status =
+      gsec_aead_crypter_nonce_length(crypter, &counter_length, error_details);
+  if (status != GRPC_STATUS_OK) {
+    goto cleanup;
+  }
+  /* Creates counters.  */
+  status =
+      alts_counter_create(is_protect ? !is_client : is_client, counter_length,
+                          overflow_size, &impl->ctr, error_details);
+  if (status != GRPC_STATUS_OK) {
+    goto cleanup;
+  }
+  /* Gets tag length.  */
+  status =
+      gsec_aead_crypter_tag_length(crypter, &impl->tag_length, error_details);
+  if (status != GRPC_STATUS_OK) {
+    goto cleanup;
+  }
+  impl->crypter = crypter;
+  impl->is_integrity_only = is_integrity_only;
+  impl->is_protect = is_protect;
+  *rp = impl;
+  return GRPC_STATUS_OK;
+cleanup:
+  alts_counter_destroy(impl->ctr);
+  gpr_free(impl);
+  return GRPC_STATUS_FAILED_PRECONDITION;
+}
+
+void alts_iovec_record_protocol_destroy(alts_iovec_record_protocol* rp) {
+  if (rp != nullptr) {
+    alts_counter_destroy(rp->ctr);
+    gsec_aead_crypter_destroy(rp->crypter);
+    gpr_free(rp);
+  }
+}
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.h b/src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.h
new file mode 100644
index 0000000000..0b7d1bf5bf
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.h
@@ -0,0 +1,199 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_IOVEC_RECORD_PROTOCOL_H
+#define GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_IOVEC_RECORD_PROTOCOL_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stdbool.h>
+
+#include "src/core/tsi/alts/crypt/gsec.h"
+
+constexpr size_t kZeroCopyFrameMessageType = 0x06;
+constexpr size_t kZeroCopyFrameLengthFieldSize = 4;
+constexpr size_t kZeroCopyFrameMessageTypeFieldSize = 4;
+constexpr size_t kZeroCopyFrameHeaderSize =
+    kZeroCopyFrameLengthFieldSize + kZeroCopyFrameMessageTypeFieldSize;
+
+// Limit k on number of frames such that at most 2^(8 * k) frames can be sent.
+constexpr size_t kAltsRecordProtocolRekeyFrameLimit = 8;
+constexpr size_t kAltsRecordProtocolFrameLimit = 5;
+
+/* An implementation of alts record protocol. The API is thread-compatible. */
+
+typedef struct iovec iovec_t;
+
+typedef struct alts_iovec_record_protocol alts_iovec_record_protocol;
+
+/**
+ * This method gets the length of record protocol frame header.
+ */
+size_t alts_iovec_record_protocol_get_header_length();
+
+/**
+ * This method gets the length of record protocol frame tag.
+ *
+ * - rp: an alts_iovec_record_protocol instance.
+ *
+ * On success, the method returns the length of record protocol frame tag.
+ * Otherwise, it returns zero.
+ */
+size_t alts_iovec_record_protocol_get_tag_length(
+    const alts_iovec_record_protocol* rp);
+
+/**
+ * This method returns maximum allowed unprotected data size, given maximum
+ * protected frame size.
+ *
+ * - rp: an alts_iovec_record_protocol instance.
+ * - max_protected_frame_size: maximum protected frame size.
+ *
+ * On success, the method returns the maximum allowed unprotected data size.
+ * Otherwise, it returns zero.
+ */
+size_t alts_iovec_record_protocol_max_unprotected_data_size(
+    const alts_iovec_record_protocol* rp, size_t max_protected_frame_size);
+
+/**
+ * This method performs integrity-only protect operation on a
+ * alts_iovec_record_protocol instance, i.e., compute frame header and tag. The
+ * caller needs to allocate the memory for header and tag prior to calling this
+ * method.
+ *
+ * - rp: an alts_iovec_record_protocol instance.
+ * - unprotected_vec: an iovec array containing unprotected data.
+ * - unprotected_vec_length: the array length of unprotected_vec.
+ * - header: an iovec containing the output frame header.
+ * - tag: an iovec containing the output frame tag.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is OK to pass nullptr into error_details.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise, it returns an
+ * error status code along with its details specified in error_details (if
+ * error_details is not nullptr).
+ */
+grpc_status_code alts_iovec_record_protocol_integrity_only_protect(
+    alts_iovec_record_protocol* rp, const iovec_t* unprotected_vec,
+    size_t unprotected_vec_length, iovec_t header, iovec_t tag,
+    char** error_details);
+
+/**
+ * This method performs integrity-only unprotect operation on a
+ * alts_iovec_record_protocol instance, i.e., verify frame header and tag.
+ *
+ * - rp: an alts_iovec_record_protocol instance.
+ * - protected_vec: an iovec array containing protected data.
+ * - protected_vec_length: the array length of protected_vec.
+ * - header: an iovec containing the frame header.
+ * - tag: an iovec containing the frame tag.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is OK to pass nullptr into error_details.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise, it returns an
+ * error status code along with its details specified in error_details (if
+ * error_details is not nullptr).
+ */
+grpc_status_code alts_iovec_record_protocol_integrity_only_unprotect(
+    alts_iovec_record_protocol* rp, const iovec_t* protected_vec,
+    size_t protected_vec_length, iovec_t header, iovec_t tag,
+    char** error_details);
+
+/**
+ * This method performs privacy-integrity protect operation on a
+ * alts_iovec_record_protocol instance, i.e., compute a protected frame. The
+ * caller needs to allocate the memory for the protected frame prior to calling
+ * this method.
+ *
+ * - rp: an alts_iovec_record_protocol instance.
+ * - unprotected_vec: an iovec array containing unprotected data.
+ * - unprotected_vec_length: the array length of unprotected_vec.
+ * - protected_frame: an iovec containing the output protected frame.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is OK to pass nullptr into error_details.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise, it returns an
+ * error status code along with its details specified in error_details (if
+ * error_details is not nullptr).
+ */
+grpc_status_code alts_iovec_record_protocol_privacy_integrity_protect(
+    alts_iovec_record_protocol* rp, const iovec_t* unprotected_vec,
+    size_t unprotected_vec_length, iovec_t protected_frame,
+    char** error_details);
+
+/**
+ * This method performs privacy-integrity unprotect operation on a
+ * alts_iovec_record_protocol instance given a full protected frame, i.e.,
+ * compute the unprotected data. The caller needs to allocated the memory for
+ * the unprotected data prior to calling this method.
+ *
+ * - rp: an alts_iovec_record_protocol instance.
+ * - header: an iovec containing the frame header.
+ * - protected_vec: an iovec array containing protected data including the tag.
+ * - protected_vec_length: the array length of protected_vec.
+ * - unprotected_data: an iovec containing the output unprotected data.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is OK to pass nullptr into error_details.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise, it returns an
+ * error status code along with its details specified in error_details (if
+ * error_details is not nullptr).
+ */
+grpc_status_code alts_iovec_record_protocol_privacy_integrity_unprotect(
+    alts_iovec_record_protocol* rp, iovec_t header,
+    const iovec_t* protected_vec, size_t protected_vec_length,
+    iovec_t unprotected_data, char** error_details);
+
+/**
+ * This method creates an alts_iovec_record_protocol instance, given a
+ * gsec_aead_crypter instance, a flag indicating if the created instance will be
+ * used at the client or server side, and a flag indicating if the created
+ * instance will be used for integrity-only mode or privacy-integrity mode. The
+ * ownership of gsec_aead_crypter instance is transferred to this new object.
+ *
+ * - crypter: a gsec_aead_crypter instance used to perform AEAD decryption.
+ * - overflow_size: overflow size of counter in bytes.
+ * - is_client: a flag indicating if the alts_iovec_record_protocol instance
+ *   will be used at the client or server side.
+ * - is_integrity_only: a flag indicating if the alts_iovec_record_protocol
+ *   instance will be used for integrity-only or privacy-integrity mode.
+ * - is_protect: a flag indicating if the alts_grpc_record_protocol instance
+ *   will be used for protect or unprotect.
+ * - rp: an alts_iovec_record_protocol instance to be returned from
+ *   the method.
+ * - error_details: a buffer containing an error message if the method does not
+ *   function correctly. It is OK to pass nullptr into error_details.
+ *
+ * On success, the method returns GRPC_STATUS_OK. Otherwise, it returns an
+ * error status code along with its details specified in error_details (if
+ * error_details is not nullptr).
+ */
+grpc_status_code alts_iovec_record_protocol_create(
+    gsec_aead_crypter* crypter, size_t overflow_size, bool is_client,
+    bool is_integrity_only, bool is_protect, alts_iovec_record_protocol** rp,
+    char** error_details);
+
+/**
+ * This method destroys an alts_iovec_record_protocol instance by de-allocating
+ * all of its occupied memory. A gsec_aead_crypter instance passed in at
+ * gsec_alts_crypter instance creation time will be destroyed in this method.
+ */
+void alts_iovec_record_protocol_destroy(alts_iovec_record_protocol* rp);
+
+#endif /* GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_IOVEC_RECORD_PROTOCOL_H \
+        */
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_zero_copy_grpc_protector.cc b/src/core/tsi/alts/zero_copy_frame_protector/alts_zero_copy_grpc_protector.cc
new file mode 100644
index 0000000000..8c764961b3
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_zero_copy_grpc_protector.cc
@@ -0,0 +1,295 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_zero_copy_grpc_protector.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/lib/gpr/useful.h"
+#include "src/core/lib/slice/slice_internal.h"
+#include "src/core/tsi/alts/crypt/gsec.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_integrity_only_record_protocol.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_privacy_integrity_record_protocol.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_grpc_record_protocol.h"
+#include "src/core/tsi/alts/zero_copy_frame_protector/alts_iovec_record_protocol.h"
+#include "src/core/tsi/transport_security_grpc.h"
+
+constexpr size_t kMinFrameLength = 1024;
+constexpr size_t kDefaultFrameLength = 16 * 1024;
+constexpr size_t kMaxFrameLength = 1024 * 1024;
+
+/**
+ * Main struct for alts_zero_copy_grpc_protector.
+ * We choose to have two alts_grpc_record_protocol objects and two sets of slice
+ * buffers: one for protect and the other for unprotect, so that protect and
+ * unprotect can be executed in parallel. Implementations of this object must be
+ * thread compatible.
+ */
+typedef struct alts_zero_copy_grpc_protector {
+  tsi_zero_copy_grpc_protector base;
+  alts_grpc_record_protocol* record_protocol;
+  alts_grpc_record_protocol* unrecord_protocol;
+  size_t max_protected_frame_size;
+  size_t max_unprotected_data_size;
+  grpc_slice_buffer unprotected_staging_sb;
+  grpc_slice_buffer protected_sb;
+  grpc_slice_buffer protected_staging_sb;
+  uint32_t parsed_frame_size;
+} alts_zero_copy_grpc_protector;
+
+/**
+ * Given a slice buffer, parses the first 4 bytes little-endian unsigned frame
+ * size and returns the total frame size including the frame field. Caller
+ * needs to make sure the input slice buffer has at least 4 bytes. Returns true
+ * on success and false on failure.
+ */
+static bool read_frame_size(const grpc_slice_buffer* sb,
+                            uint32_t* total_frame_size) {
+  if (sb == nullptr || sb->length < kZeroCopyFrameLengthFieldSize) {
+    return false;
+  }
+  uint8_t frame_size_buffer[kZeroCopyFrameLengthFieldSize];
+  uint8_t* buf = frame_size_buffer;
+  /* Copies the first 4 bytes to a temporary buffer.  */
+  size_t remaining = kZeroCopyFrameLengthFieldSize;
+  for (size_t i = 0; i < sb->count; i++) {
+    size_t slice_length = GRPC_SLICE_LENGTH(sb->slices[i]);
+    if (remaining <= slice_length) {
+      memcpy(buf, GRPC_SLICE_START_PTR(sb->slices[i]), remaining);
+      remaining = 0;
+      break;
+    } else {
+      memcpy(buf, GRPC_SLICE_START_PTR(sb->slices[i]), slice_length);
+      buf += slice_length;
+      remaining -= slice_length;
+    }
+  }
+  GPR_ASSERT(remaining == 0);
+  /* Gets little-endian frame size.  */
+  uint32_t frame_size = (((uint32_t)frame_size_buffer[3]) << 24) |
+                        (((uint32_t)frame_size_buffer[2]) << 16) |
+                        (((uint32_t)frame_size_buffer[1]) << 8) |
+                        ((uint32_t)frame_size_buffer[0]);
+  if (frame_size > kMaxFrameLength) {
+    gpr_log(GPR_ERROR, "Frame size is larger than maximum frame size");
+    return false;
+  }
+  /* Returns frame size including frame length field.  */
+  *total_frame_size =
+      static_cast<uint32_t>(frame_size + kZeroCopyFrameLengthFieldSize);
+  return true;
+}
+
+/**
+ * Creates an alts_grpc_record_protocol object, given key, key size, and flags
+ * to indicate whether the record_protocol object uses the rekeying AEAD,
+ * whether the object is for client or server, whether the object is for
+ * integrity-only or privacy-integrity mode, and whether the object is is used
+ * for protect or unprotect.
+ */
+static tsi_result create_alts_grpc_record_protocol(
+    const uint8_t* key, size_t key_size, bool is_rekey, bool is_client,
+    bool is_integrity_only, bool is_protect,
+    alts_grpc_record_protocol** record_protocol) {
+  if (key == nullptr || record_protocol == nullptr) {
+    return TSI_INVALID_ARGUMENT;
+  }
+  grpc_status_code status;
+  gsec_aead_crypter* crypter = nullptr;
+  char* error_details = nullptr;
+  status = gsec_aes_gcm_aead_crypter_create(key, key_size, kAesGcmNonceLength,
+                                            kAesGcmTagLength, is_rekey,
+                                            &crypter, &error_details);
+  if (status != GRPC_STATUS_OK) {
+    gpr_log(GPR_ERROR, "Failed to create AEAD crypter, %s", error_details);
+    gpr_free(error_details);
+    return TSI_INTERNAL_ERROR;
+  }
+  size_t overflow_limit = is_rekey ? kAltsRecordProtocolRekeyFrameLimit
+                                   : kAltsRecordProtocolFrameLimit;
+  /* Creates alts_grpc_record_protocol with AEAD crypter ownership transferred.
+   */
+  tsi_result result =
+      is_integrity_only
+          ? alts_grpc_integrity_only_record_protocol_create(
+                crypter, overflow_limit, is_client, is_protect, record_protocol)
+          : alts_grpc_privacy_integrity_record_protocol_create(
+                crypter, overflow_limit, is_client, is_protect,
+                record_protocol);
+  if (result != TSI_OK) {
+    gsec_aead_crypter_destroy(crypter);
+    return result;
+  }
+  return TSI_OK;
+}
+
+/* --- tsi_zero_copy_grpc_protector methods implementation. --- */
+
+static tsi_result alts_zero_copy_grpc_protector_protect(
+    tsi_zero_copy_grpc_protector* self, grpc_slice_buffer* unprotected_slices,
+    grpc_slice_buffer* protected_slices) {
+  if (self == nullptr || unprotected_slices == nullptr ||
+      protected_slices == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid nullptr arguments to zero-copy grpc protect.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_zero_copy_grpc_protector* protector =
+      reinterpret_cast<alts_zero_copy_grpc_protector*>(self);
+  /* Calls alts_grpc_record_protocol protect repeatly.  */
+  while (unprotected_slices->length > protector->max_unprotected_data_size) {
+    grpc_slice_buffer_move_first(unprotected_slices,
+                                 protector->max_unprotected_data_size,
+                                 &protector->unprotected_staging_sb);
+    tsi_result status = alts_grpc_record_protocol_protect(
+        protector->record_protocol, &protector->unprotected_staging_sb,
+        protected_slices);
+    if (status != TSI_OK) {
+      return status;
+    }
+  }
+  return alts_grpc_record_protocol_protect(
+      protector->record_protocol, unprotected_slices, protected_slices);
+}
+
+static tsi_result alts_zero_copy_grpc_protector_unprotect(
+    tsi_zero_copy_grpc_protector* self, grpc_slice_buffer* protected_slices,
+    grpc_slice_buffer* unprotected_slices) {
+  if (self == nullptr || unprotected_slices == nullptr ||
+      protected_slices == nullptr) {
+    gpr_log(GPR_ERROR,
+            "Invalid nullptr arguments to zero-copy grpc unprotect.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  alts_zero_copy_grpc_protector* protector =
+      reinterpret_cast<alts_zero_copy_grpc_protector*>(self);
+  grpc_slice_buffer_move_into(protected_slices, &protector->protected_sb);
+  /* Keep unprotecting each frame if possible.  */
+  while (protector->protected_sb.length >= kZeroCopyFrameLengthFieldSize) {
+    if (protector->parsed_frame_size == 0) {
+      /* We have not parsed frame size yet. Parses frame size.  */
+      if (!read_frame_size(&protector->protected_sb,
+                           &protector->parsed_frame_size)) {
+        grpc_slice_buffer_reset_and_unref_internal(&protector->protected_sb);
+        return TSI_DATA_CORRUPTED;
+      }
+    }
+    if (protector->protected_sb.length < protector->parsed_frame_size) break;
+    /* At this point, protected_sb contains at least one frame of data.  */
+    tsi_result status;
+    if (protector->protected_sb.length == protector->parsed_frame_size) {
+      status = alts_grpc_record_protocol_unprotect(protector->unrecord_protocol,
+                                                   &protector->protected_sb,
+                                                   unprotected_slices);
+    } else {
+      grpc_slice_buffer_move_first(&protector->protected_sb,
+                                   protector->parsed_frame_size,
+                                   &protector->protected_staging_sb);
+      status = alts_grpc_record_protocol_unprotect(
+          protector->unrecord_protocol, &protector->protected_staging_sb,
+          unprotected_slices);
+    }
+    protector->parsed_frame_size = 0;
+    if (status != TSI_OK) {
+      grpc_slice_buffer_reset_and_unref_internal(&protector->protected_sb);
+      return status;
+    }
+  }
+  return TSI_OK;
+}
+
+static void alts_zero_copy_grpc_protector_destroy(
+    tsi_zero_copy_grpc_protector* self) {
+  if (self == nullptr) {
+    return;
+  }
+  alts_zero_copy_grpc_protector* protector =
+      reinterpret_cast<alts_zero_copy_grpc_protector*>(self);
+  alts_grpc_record_protocol_destroy(protector->record_protocol);
+  alts_grpc_record_protocol_destroy(protector->unrecord_protocol);
+  grpc_slice_buffer_destroy_internal(&protector->unprotected_staging_sb);
+  grpc_slice_buffer_destroy_internal(&protector->protected_sb);
+  grpc_slice_buffer_destroy_internal(&protector->protected_staging_sb);
+  gpr_free(protector);
+}
+
+static const tsi_zero_copy_grpc_protector_vtable
+    alts_zero_copy_grpc_protector_vtable = {
+        alts_zero_copy_grpc_protector_protect,
+        alts_zero_copy_grpc_protector_unprotect,
+        alts_zero_copy_grpc_protector_destroy};
+
+tsi_result alts_zero_copy_grpc_protector_create(
+    const uint8_t* key, size_t key_size, bool is_rekey, bool is_client,
+    bool is_integrity_only, size_t* max_protected_frame_size,
+    tsi_zero_copy_grpc_protector** protector) {
+  if (grpc_core::ExecCtx::Get() == nullptr || key == nullptr ||
+      protector == nullptr) {
+    gpr_log(
+        GPR_ERROR,
+        "Invalid nullptr arguments to alts_zero_copy_grpc_protector create.");
+    return TSI_INVALID_ARGUMENT;
+  }
+  /* Creates alts_zero_copy_protector.  */
+  alts_zero_copy_grpc_protector* impl =
+      static_cast<alts_zero_copy_grpc_protector*>(
+          gpr_zalloc(sizeof(alts_zero_copy_grpc_protector)));
+  /* Creates alts_grpc_record_protocol objects.  */
+  tsi_result status = create_alts_grpc_record_protocol(
+      key, key_size, is_rekey, is_client, is_integrity_only,
+      /*is_protect=*/true, &impl->record_protocol);
+  if (status == TSI_OK) {
+    status = create_alts_grpc_record_protocol(
+        key, key_size, is_rekey, is_client, is_integrity_only,
+        /*is_protect=*/false, &impl->unrecord_protocol);
+    if (status == TSI_OK) {
+      /* Sets maximum frame size.  */
+      size_t max_protected_frame_size_to_set = kDefaultFrameLength;
+      if (max_protected_frame_size != nullptr) {
+        *max_protected_frame_size =
+            GPR_MIN(*max_protected_frame_size, kMaxFrameLength);
+        *max_protected_frame_size =
+            GPR_MAX(*max_protected_frame_size, kMinFrameLength);
+        max_protected_frame_size_to_set = *max_protected_frame_size;
+      }
+      impl->max_protected_frame_size = max_protected_frame_size_to_set;
+      impl->max_unprotected_data_size =
+          alts_grpc_record_protocol_max_unprotected_data_size(
+              impl->record_protocol, max_protected_frame_size_to_set);
+      GPR_ASSERT(impl->max_unprotected_data_size > 0);
+      /* Allocates internal slice buffers.  */
+      grpc_slice_buffer_init(&impl->unprotected_staging_sb);
+      grpc_slice_buffer_init(&impl->protected_sb);
+      grpc_slice_buffer_init(&impl->protected_staging_sb);
+      impl->parsed_frame_size = 0;
+      impl->base.vtable = &alts_zero_copy_grpc_protector_vtable;
+      *protector = &impl->base;
+      return TSI_OK;
+    }
+  }
+
+  /* Cleanup if create failed.  */
+  alts_grpc_record_protocol_destroy(impl->record_protocol);
+  alts_grpc_record_protocol_destroy(impl->unrecord_protocol);
+  gpr_free(impl);
+  return TSI_INTERNAL_ERROR;
+}
diff --git a/src/core/tsi/alts/zero_copy_frame_protector/alts_zero_copy_grpc_protector.h b/src/core/tsi/alts/zero_copy_frame_protector/alts_zero_copy_grpc_protector.h
new file mode 100644
index 0000000000..71e953cfc1
--- /dev/null
+++ b/src/core/tsi/alts/zero_copy_frame_protector/alts_zero_copy_grpc_protector.h
@@ -0,0 +1,52 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_ZERO_COPY_GRPC_PROTECTOR_H
+#define GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_ZERO_COPY_GRPC_PROTECTOR_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stdbool.h>
+
+#include "src/core/tsi/transport_security_grpc.h"
+
+/**
+ * This method creates an ALTS zero-copy grpc protector.
+ *
+ * - key: a symmetric key used to seal/unseal frames.
+ * - key_size: the size of symmetric key.
+ * - is_rekey: use rekeying AEAD crypter.
+ * - is_client: a flag indicating if the protector will be used at client or
+ *   server side.
+ * - is_integrity_only: a flag indicating if the protector instance will be
+ *   used for integrity-only or privacy-integrity mode.
+ * - max_protected_frame_size: an in/out parameter indicating max frame size
+ *   to be used by the protector. If it is nullptr, the default frame size will
+ *   be used. Otherwise, the provided frame size will be adjusted (if not
+ *   falling into a valid frame range) and used.
+ * - protector: a pointer to the zero-copy protector returned from the method.
+ *
+ * This method returns TSI_OK on success or a specific error code otherwise.
+ */
+tsi_result alts_zero_copy_grpc_protector_create(
+    const uint8_t* key, size_t key_size, bool is_rekey, bool is_client,
+    bool is_integrity_only, size_t* max_protected_frame_size,
+    tsi_zero_copy_grpc_protector** protector);
+
+#endif /* GRPC_CORE_TSI_ALTS_ZERO_COPY_FRAME_PROTECTOR_ALTS_ZERO_COPY_GRPC_PROTECTOR_H \
+        */