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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 <iosfwd>
#include <tuple>
#include "base/base_export.h"
#include "base/hash.h"
#include "base/logging.h"
#include "base/token.h"
namespace base {
struct UnguessableTokenHash;
// UnguessableToken is, like Token, a randomly chosen 128-bit value. Unlike
// Token however, a new UnguessableToken must always be generated at runtime
// from a cryptographically strong random source (or copied or serialized and
// deserialized from another such UnguessableToken). It can be used as part of a
// larger aggregate type, or as an ID in and of itself.
//
// UnguessableToken can be used to implement "Capability-Based Security".
// In other words, 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 against 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,
// base::Optional should be used 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;
// 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();
}
bool is_empty() const { return token_.is_zero(); }
// Hex representation of the unguessable token.
std::string ToString() const { return token_.ToString(); }
explicit operator bool() const { return !is_empty(); }
bool operator<(const UnguessableToken& other) const {
return token_ < other.token_;
}
bool operator==(const UnguessableToken& other) const {
return token_ == other.token_;
}
bool operator!=(const UnguessableToken& other) const {
return !(*this == other);
}
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_
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