1 files changed, 59 insertions, 0 deletions
diff --git a/Firestore/core/src/firebase/firestore/util/secure_random.h b/Firestore/core/src/firebase/firestore/util/secure_random.h
new file mode 100644
index 0000000..72be1bd
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/util/secure_random.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright 2017 Google
+ *
+ * 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 FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_SECURE_RANDOM_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_SECURE_RANDOM_H_
+
+#include <stdint.h>
+
+#include <limits>
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+// A "secure" pseudorandom number generator, suitable for generating
+// unguessable identifiers. This exists because
+//
+//   * std::mt19937 is blazing fast but its outputs can be guessed once enough
+//     previous outputs have been observed.
+//   * std::random_device isn't guaranteed to come from a secure PRNG or be
+//     fast.
+//
+// The implementation satisfies the C++11 UniformRandomBitGenerator concept and
+// delegates to an implementation that generates high quality random values
+// quickly with periodic reseeding.
+class SecureRandom {
+ public:
+  // C++11 UniformRandomBitGenerator interface
+  using result_type = uint32_t;
+
+  static constexpr result_type min() {
+    return std::numeric_limits<result_type>::min();
+  }
+
+  static constexpr result_type max() {
+    return std::numeric_limits<result_type>::max();
+  }
+
+  result_type operator()();
+};
+
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_SECURE_RANDOM_H_