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// Copyright 2017 The Abseil 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
//
// https://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 "absl/random/internal/seed_material.h"
#include <fcntl.h>
#ifndef _WIN32
#include <unistd.h>
#else
#include <io.h>
#endif
#include <algorithm>
#include <cerrno>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include "absl/base/internal/raw_logging.h"
#include "absl/strings/ascii.h"
#include "absl/strings/escaping.h"
#include "absl/strings/string_view.h"
#include "absl/strings/strip.h"
#if defined(__native_client__)
#include <nacl/nacl_random.h>
#define ABSL_RANDOM_USE_NACL_SECURE_RANDOM 1
#elif defined(_WIN32)
#include <windows.h>
#define ABSL_RANDOM_USE_BCRYPT 1
#pragma comment(lib, "bcrypt.lib")
#elif defined(__Fuchsia__)
#include <zircon/syscalls.h>
#endif
#if defined(ABSL_RANDOM_USE_BCRYPT)
#include <bcrypt.h>
#ifndef BCRYPT_SUCCESS
#define BCRYPT_SUCCESS(Status) (((NTSTATUS)(Status)) >= 0)
#endif
// Also link bcrypt; this can be done via linker options or:
// #pragma comment(lib, "bcrypt.lib")
#endif
namespace absl {
namespace random_internal {
namespace {
// Read OS Entropy for random number seeds.
// TODO(absl-team): Possibly place a cap on how much entropy may be read at a
// time.
#if defined(ABSL_RANDOM_USE_BCRYPT)
// On Windows potentially use the BCRYPT CNG API to read available entropy.
bool ReadSeedMaterialFromOSEntropyImpl(absl::Span<uint32_t> values) {
BCRYPT_ALG_HANDLE hProvider;
NTSTATUS ret;
ret = BCryptOpenAlgorithmProvider(&hProvider, BCRYPT_RNG_ALGORITHM,
MS_PRIMITIVE_PROVIDER, 0);
if (!(BCRYPT_SUCCESS(ret))) {
ABSL_RAW_LOG(ERROR, "Failed to open crypto provider.");
return false;
}
ret = BCryptGenRandom(
hProvider, // provider
reinterpret_cast<UCHAR*>(values.data()), // buffer
static_cast<ULONG>(sizeof(uint32_t) * values.size()), // bytes
0); // flags
BCryptCloseAlgorithmProvider(hProvider, 0);
return BCRYPT_SUCCESS(ret);
}
#elif defined(ABSL_RANDOM_USE_NACL_SECURE_RANDOM)
// On NaCL use nacl_secure_random to acquire bytes.
bool ReadSeedMaterialFromOSEntropyImpl(absl::Span<uint32_t> values) {
auto buffer = reinterpret_cast<uint8_t*>(values.data());
size_t buffer_size = sizeof(uint32_t) * values.size();
uint8_t* output_ptr = buffer;
while (buffer_size > 0) {
size_t nread = 0;
const int error = nacl_secure_random(output_ptr, buffer_size, &nread);
if (error != 0 || nread > buffer_size) {
ABSL_RAW_LOG(ERROR, "Failed to read secure_random seed data: %d", error);
return false;
}
output_ptr += nread;
buffer_size -= nread;
}
return true;
}
#elif defined(__Fuchsia__)
bool ReadSeedMaterialFromOSEntropyImpl(absl::Span<uint32_t> values) {
auto buffer = reinterpret_cast<uint8_t*>(values.data());
size_t buffer_size = sizeof(uint32_t) * values.size();
zx_cprng_draw(buffer, buffer_size);
return true;
}
#else
// On *nix, read entropy from /dev/urandom.
bool ReadSeedMaterialFromOSEntropyImpl(absl::Span<uint32_t> values) {
const char kEntropyFile[] = "/dev/urandom";
auto buffer = reinterpret_cast<uint8_t*>(values.data());
size_t buffer_size = sizeof(uint32_t) * values.size();
int dev_urandom = open(kEntropyFile, O_RDONLY);
bool success = (-1 != dev_urandom);
if (!success) {
return false;
}
while (success && buffer_size > 0) {
int bytes_read = read(dev_urandom, buffer, buffer_size);
int read_error = errno;
success = (bytes_read > 0);
if (success) {
buffer += bytes_read;
buffer_size -= bytes_read;
} else if (bytes_read == -1 && read_error == EINTR) {
success = true; // Need to try again.
}
}
close(dev_urandom);
return success;
}
#endif
} // namespace
bool ReadSeedMaterialFromOSEntropy(absl::Span<uint32_t> values) {
assert(values.data() != nullptr);
if (values.data() == nullptr) {
return false;
}
if (values.empty()) {
return true;
}
return ReadSeedMaterialFromOSEntropyImpl(values);
}
void MixIntoSeedMaterial(absl::Span<const uint32_t> sequence,
absl::Span<uint32_t> seed_material) {
// Algorithm is based on code available at
// https://gist.github.com/imneme/540829265469e673d045
constexpr uint32_t kInitVal = 0x43b0d7e5;
constexpr uint32_t kHashMul = 0x931e8875;
constexpr uint32_t kMixMulL = 0xca01f9dd;
constexpr uint32_t kMixMulR = 0x4973f715;
constexpr uint32_t kShiftSize = sizeof(uint32_t) * 8 / 2;
uint32_t hash_const = kInitVal;
auto hash = [&](uint32_t value) {
value ^= hash_const;
hash_const *= kHashMul;
value *= hash_const;
value ^= value >> kShiftSize;
return value;
};
auto mix = [&](uint32_t x, uint32_t y) {
uint32_t result = kMixMulL * x - kMixMulR * y;
result ^= result >> kShiftSize;
return result;
};
for (const auto& seq_val : sequence) {
for (auto& elem : seed_material) {
elem = mix(elem, hash(seq_val));
}
}
}
absl::optional<uint32_t> GetSaltMaterial() {
// Salt must be common for all generators within the same process so read it
// only once and store in static variable.
static const auto salt_material = []() -> absl::optional<uint32_t> {
uint32_t salt_value = 0;
if (random_internal::ReadSeedMaterialFromOSEntropy(
MakeSpan(&salt_value, 1))) {
return salt_value;
}
return absl::nullopt;
}();
return salt_material;
}
} // namespace random_internal
} // namespace absl
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