1 // Copyright 2016 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_UNGUESSABLE_TOKEN_H_ 6 #define BASE_UNGUESSABLE_TOKEN_H_ 7 8 #include <stdint.h> 9 #include <string.h> 10 #include <iosfwd> 11 #include <tuple> 12 13 #include "base/base_export.h" 14 #include "base/hash.h" 15 #include "base/logging.h" 16 #include "base/token.h" 17 18 namespace base { 19 20 struct UnguessableTokenHash; 21 22 // UnguessableToken is, like Token, a randomly chosen 128-bit value. Unlike 23 // Token however, a new UnguessableToken must always be generated at runtime 24 // from a cryptographically strong random source (or copied or serialized and 25 // deserialized from another such UnguessableToken). It can be used as part of a 26 // larger aggregate type, or as an ID in and of itself. 27 // 28 // UnguessableToken can be used to implement "Capability-Based Security". 29 // In other words, UnguessableToken can be used when the resource associated 30 // with the ID needs to be protected against manipulation by other untrusted 31 // agents in the system, and there is no other convenient way to verify the 32 // authority of the agent to do so (because the resource is part of a table 33 // shared across processes, for instance). In such a scheme, knowledge of the 34 // token value in and of itself is sufficient proof of authority to carry out 35 // an operation against the associated resource. 36 // 37 // Use Create() for creating new UnguessableTokens. 38 // 39 // NOTE: It is illegal to send empty UnguessableTokens across processes, and 40 // sending/receiving empty tokens should be treated as a security issue. 41 // If there is a valid scenario for sending "no token" across processes, 42 // base::Optional should be used instead of an empty token. 43 class BASE_EXPORT UnguessableToken { 44 public: 45 // Create a unique UnguessableToken. 46 static UnguessableToken Create(); 47 48 // Returns a reference to a global null UnguessableToken. This should only be 49 // used for functions that need to return a reference to an UnguessableToken, 50 // and should not be used as a general-purpose substitute for invoking the 51 // default constructor. 52 static const UnguessableToken& Null(); 53 54 // Return a UnguessableToken built from the high/low bytes provided. 55 // It should only be used in deserialization scenarios. 56 // 57 // NOTE: If the deserialized token is empty, it means that it was never 58 // initialized via Create(). This is a security issue, and should be handled. 59 static UnguessableToken Deserialize(uint64_t high, uint64_t low); 60 61 // Creates an empty UnguessableToken. 62 // Assign to it with Create() before using it. 63 constexpr UnguessableToken() = default; 64 65 // NOTE: Serializing an empty UnguessableToken is an illegal operation. GetHighForSerialization()66 uint64_t GetHighForSerialization() const { 67 DCHECK(!is_empty()); 68 return token_.high(); 69 } 70 71 // NOTE: Serializing an empty UnguessableToken is an illegal operation. GetLowForSerialization()72 uint64_t GetLowForSerialization() const { 73 DCHECK(!is_empty()); 74 return token_.low(); 75 } 76 is_empty()77 bool is_empty() const { return token_.is_zero(); } 78 79 // Hex representation of the unguessable token. ToString()80 std::string ToString() const { return token_.ToString(); } 81 82 explicit operator bool() const { return !is_empty(); } 83 84 bool operator<(const UnguessableToken& other) const { 85 return token_ < other.token_; 86 } 87 88 bool operator==(const UnguessableToken& other) const { 89 return token_ == other.token_; 90 } 91 92 bool operator!=(const UnguessableToken& other) const { 93 return !(*this == other); 94 } 95 96 private: 97 friend struct UnguessableTokenHash; 98 explicit UnguessableToken(const Token& token); 99 100 base::Token token_; 101 }; 102 103 BASE_EXPORT std::ostream& operator<<(std::ostream& out, 104 const UnguessableToken& token); 105 106 // For use in std::unordered_map. 107 struct UnguessableTokenHash { operatorUnguessableTokenHash108 size_t operator()(const base::UnguessableToken& token) const { 109 DCHECK(token); 110 return TokenHash()(token.token_); 111 } 112 }; 113 114 } // namespace base 115 116 #endif // BASE_UNGUESSABLE_TOKEN_H_ 117