Add base::UnguessableToken

base/unguessable_token.h

Index: base/unguessable_token.h
diff --git a/base/unguessable_token.h b/base/unguessable_token.h
new file mode 100644
index 0000000000000000000000000000000000000000..64b1868886f2f0d06c613efa79a1f84ceb7b3c59
--- /dev/null
+++ b/base/unguessable_token.h
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_UNGUESSABLE_TOKEN_H_
+#define BASE_UNGUESSABLE_TOKEN_H_
+
+#include <stdint.h>
+#include <string.h>
+#include <tuple>
+
+#include "base/base_export.h"
+#include "base/hash.h"
+#include "base/logging.h"
+
+namespace base {
+
+struct UnguessableTokenHash;
+
+// A UnguessableToken is an 128-bit token generated from a cryptographically
+// strong random source.
+//
+// UnguessableToken should be used when a sensitive ID needs to be unguessable,
+// and is shared across processes. It can be used as part of a larger aggregate
+// type, or as an ID in and of itself.
+//
+// Use Create() for creating new UnguessableTokens.
+//
+// NOTE: It is illegal to send empty UnguessableTokens across processes, and
+// sending/receiving empty tokens should be treated as a security issue.
+// If there is a valid scenario for sending "no token" across processes,
+// base::Optional should be used instead of an empty token.
+class BASE_EXPORT UnguessableToken {
+ public:
+  // Create a unique UnguessableToken.
+  static UnguessableToken Create();
+
+  // Return a UnguessableToken built from the high/low bytes provided.
+  // It should only be used in deserialization scenarios.
+  //
+  // NOTE: If the deserialized token is empty, it means that it was never
+  // initialized via Create(). This is a security issue, and should be handled.
+  static UnguessableToken Deserialize(uint64_t high, uint64_t low);
+
+  // Creates an empty UnguessableToken.
+  // Assign to it with Create() before using it.
+  UnguessableToken() = default;
+
+  // NOTE: Serializing an empty UnguessableToken is an illegal operation.
+  uint64_t GetHighForSerialization() const {
+    DCHECK(!is_empty());
+    return high_;
+  };
+
+  // NOTE: Serializing an empty UnguessableToken is an illegal operation.
+  uint64_t GetLowForSerialization() const {
+    DCHECK(!is_empty());
+    return low_;
+  }
+
+  bool is_empty() const { return high_ == 0 && low_ == 0; }
+
+  std::string ToString() const;
+
+  explicit operator bool() const { return !is_empty(); }
+
+  bool operator<(const UnguessableToken& other) const {
+    return std::tie(high_, low_) < std::tie(other.high_, other.low_);
+  }
+
+  bool operator==(const UnguessableToken& other) const {
+    return high_ == other.high_ && low_ == other.low_;
+  }
+
+  bool operator!=(const UnguessableToken& other) const {
+    return !(*this == other);
+  }
+
+ private:
+  friend struct UnguessableTokenHash;
+  UnguessableToken(uint64_t high, uint64_t low);
+
+  // Note: Two uint64_t are used instead of uint8_t[16], in order to have a
+  // simpler ToString() and is_empty().
+  uint64_t high_ = 0;
+  uint64_t low_ = 0;
+};
+
+// For use in std::unordered_map.
+struct UnguessableTokenHash {
+  size_t operator()(const base::UnguessableToken& token) const {
+    DCHECK(token);
+    return base::HashInts64(token.high_, token.low_);
+  }
+};
+
+}  // namespace base
+
+#endif  // BASE_UNGUESSABLE_TOKEN_H_