// Copyright 2016 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_UNGUESSABLE_TOKEN_H_
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#define BASE_UNGUESSABLE_TOKEN_H_
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#include <stdint.h>
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#include <string.h>
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#include <iosfwd>
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#include <tuple>
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#include "base/base_export.h"
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#include "base/hash.h"
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#include "base/logging.h"
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namespace base {
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struct UnguessableTokenHash;
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// A UnguessableToken is an 128-bit token generated from a cryptographically
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// strong random source. It can be used as part of a larger aggregate type,
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// or as an ID in and of itself.
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//
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// UnguessableToken can be used to implement "Capability-Based Security".
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// In other words, UnguessableToken can be used when the resource associated
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// with the ID needs to be protected against manipulation by other untrusted
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// agents in the system, and there is no other convenient way to verify the
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// authority of the agent to do so (because the resource is part of a table
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// shared across processes, for instance). In such a scheme, knowledge of the
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// token value in and of itself is sufficient proof of authority to carry out
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// an operation against the associated resource.
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//
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// Use Create() for creating new UnguessableTokens.
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//
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// NOTE: It is illegal to send empty UnguessableTokens across processes, and
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// sending/receiving empty tokens should be treated as a security issue.
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// If there is a valid scenario for sending "no token" across processes,
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// base::Optional should be used instead of an empty token.
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class BASE_EXPORT UnguessableToken {
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public:
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// Create a unique UnguessableToken.
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static UnguessableToken Create();
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// Return a UnguessableToken built from the high/low bytes provided.
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// It should only be used in deserialization scenarios.
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//
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// NOTE: If the deserialized token is empty, it means that it was never
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// initialized via Create(). This is a security issue, and should be handled.
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static UnguessableToken Deserialize(uint64_t high, uint64_t low);
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// Creates an empty UnguessableToken.
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// Assign to it with Create() before using it.
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constexpr UnguessableToken() = default;
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// NOTE: Serializing an empty UnguessableToken is an illegal operation.
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uint64_t GetHighForSerialization() const {
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DCHECK(!is_empty());
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return high_;
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}
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// NOTE: Serializing an empty UnguessableToken is an illegal operation.
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uint64_t GetLowForSerialization() const {
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DCHECK(!is_empty());
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return low_;
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}
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bool is_empty() const { return high_ == 0 && low_ == 0; }
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// Hex representation of the unguessable token.
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std::string ToString() const;
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explicit operator bool() const { return !is_empty(); }
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bool operator<(const UnguessableToken& other) const {
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return std::tie(high_, low_) < std::tie(other.high_, other.low_);
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}
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bool operator==(const UnguessableToken& other) const {
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return high_ == other.high_ && low_ == other.low_;
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}
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bool operator!=(const UnguessableToken& other) const {
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return !(*this == other);
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}
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private:
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friend struct UnguessableTokenHash;
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UnguessableToken(uint64_t high, uint64_t low);
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// Note: Two uint64_t are used instead of uint8_t[16], in order to have a
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// simpler ToString() and is_empty().
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uint64_t high_ = 0;
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uint64_t low_ = 0;
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};
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BASE_EXPORT std::ostream& operator<<(std::ostream& out,
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const UnguessableToken& token);
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// For use in std::unordered_map.
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struct UnguessableTokenHash {
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size_t operator()(const base::UnguessableToken& token) const {
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DCHECK(token);
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return base::HashInts64(token.high_, token.low_);
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}
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};
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} // namespace base
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#endif // BASE_UNGUESSABLE_TOKEN_H_
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