// 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 #include #include #include #include "base/base_export.h" #include "base/check.h" #include "base/hash/hash.h" #include "base/token.h" namespace base { struct UnguessableTokenHash; // UnguessableToken is, like Token, a randomly chosen 128-bit value. Unlike // Token, a new UnguessableToken is always generated at runtime from a // cryptographically strong random source (or copied or serialized and // deserialized from another such UnguessableToken). Also unlike Token, the == // and != operators are constant time. It can be used as part of a larger // aggregate type, or as an ID in and of itself. // // An UnguessableToken is a strong *bearer token*. Bearer tokens are like HTTP // cookies: if a caller has the token, the callee thereby considers the caller // authorized to request the operation the callee performs. // // UnguessableToken can be used when the resource associated with the ID needs // to be protected against manipulation by other untrusted agents in the system, // and there is no other convenient way to verify the authority of the agent to // do so (because the resource is part of a table shared across processes, for // instance). In such a scheme, knowledge of the token value in and of itself is // sufficient proof of authority to carry out an operation on the associated // resource. // // 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, use // absl::optional instead of an empty token. class BASE_EXPORT UnguessableToken { public: // Create a unique UnguessableToken. static UnguessableToken Create(); // Returns a reference to a global null UnguessableToken. This should only be // used for functions that need to return a reference to an UnguessableToken, // and should not be used as a general-purpose substitute for invoking the // default constructor. static const UnguessableToken& Null(); // 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. constexpr UnguessableToken() = default; constexpr UnguessableToken(const UnguessableToken&) = default; constexpr UnguessableToken& operator=(const UnguessableToken&) = default; constexpr UnguessableToken(UnguessableToken&&) noexcept = default; constexpr UnguessableToken& operator=(UnguessableToken&&) = default; // NOTE: Serializing an empty UnguessableToken is an illegal operation. uint64_t GetHighForSerialization() const { DCHECK(!is_empty()); return token_.high(); } // NOTE: Serializing an empty UnguessableToken is an illegal operation. uint64_t GetLowForSerialization() const { DCHECK(!is_empty()); return token_.low(); } constexpr bool is_empty() const { return token_.is_zero(); } // Hex representation of the unguessable token. std::string ToString() const { return token_.ToString(); } explicit constexpr operator bool() const { return !is_empty(); } span AsBytes() const { return token_.AsBytes(); } constexpr bool operator<(const UnguessableToken& other) const { return token_ < other.token_; } bool operator==(const UnguessableToken& other) const; bool operator!=(const UnguessableToken& other) const { return !(*this == other); } #if defined(UNIT_TEST) static UnguessableToken CreateForTesting(uint64_t high, uint64_t low) { return Deserialize(high, low); } #endif private: friend struct UnguessableTokenHash; explicit UnguessableToken(const Token& token); base::Token token_; }; BASE_EXPORT std::ostream& operator<<(std::ostream& out, const UnguessableToken& token); // For use in std::unordered_map. struct UnguessableTokenHash { size_t operator()(const base::UnguessableToken& token) const { DCHECK(token); return TokenHash()(token.token_); } }; } // namespace base #endif // BASE_UNGUESSABLE_TOKEN_H_