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- // Copyright (c) 2012 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.
- // Utility class for calculating the HMAC for a given message. We currently only
- // support SHA-1 and SHA-256 for the hash algorithm, but this can be extended
- // easily. Prefer the base::span and std::vector overloads over the
- // base::StringPiece and std::string overloads.
- #ifndef CRYPTO_HMAC_H_
- #define CRYPTO_HMAC_H_
- #include <stddef.h>
- #include <memory>
- #include <vector>
- #include "base/containers/span.h"
- #include "base/strings/string_piece.h"
- #include "crypto/crypto_export.h"
- namespace crypto {
- // Simplify the interface and reduce includes by abstracting out the internals.
- class SymmetricKey;
- class CRYPTO_EXPORT HMAC {
- public:
- // The set of supported hash functions. Extend as required.
- enum HashAlgorithm {
- SHA1,
- SHA256,
- };
- explicit HMAC(HashAlgorithm hash_alg);
- HMAC(const HMAC&) = delete;
- HMAC& operator=(const HMAC&) = delete;
- ~HMAC();
- // Returns the length of digest that this HMAC will create.
- size_t DigestLength() const;
- // TODO(abarth): Add a PreferredKeyLength() member function.
- // Initializes this instance using |key| of the length |key_length|. Call Init
- // only once. It returns false on the second or later calls.
- //
- // NOTE: the US Federal crypto standard FIPS 198, Section 3 says:
- // The size of the key, K, shall be equal to or greater than L/2, where L
- // is the size of the hash function output.
- // In FIPS 198-1 (and SP-800-107, which describes key size recommendations),
- // this requirement is gone. But a system crypto library may still enforce
- // this old requirement. If the key is shorter than this recommended value,
- // Init() may fail.
- [[nodiscard]] bool Init(const unsigned char* key, size_t key_length);
- // Initializes this instance using |key|. Call Init
- // only once. It returns false on the second or later calls.
- [[nodiscard]] bool Init(const SymmetricKey* key);
- // Initializes this instance using |key|. Call Init only once. It returns
- // false on the second or later calls.
- [[nodiscard]] bool Init(base::StringPiece key) {
- return Init(base::as_bytes(base::make_span(key)));
- }
- // Initializes this instance using |key|. Call Init only once. It returns
- // false on the second or later calls.
- [[nodiscard]] bool Init(base::span<const uint8_t> key) {
- return Init(key.data(), key.size());
- }
- // Calculates the HMAC for the message in |data| using the algorithm supplied
- // to the constructor and the key supplied to the Init method. The HMAC is
- // returned in |digest|, which has |digest_length| bytes of storage available.
- // If |digest_length| is smaller than DigestLength(), the output will be
- // truncated. If it is larger, this method will fail.
- [[nodiscard]] bool Sign(base::StringPiece data,
- unsigned char* digest,
- size_t digest_length) const;
- [[nodiscard]] bool Sign(base::span<const uint8_t> data,
- base::span<uint8_t> digest) const;
- // Verifies that the HMAC for the message in |data| equals the HMAC provided
- // in |digest|, using the algorithm supplied to the constructor and the key
- // supplied to the Init method. Use of this method is strongly recommended
- // over using Sign() with a manual comparison (such as memcmp), as such
- // comparisons may result in side-channel disclosures, such as timing, that
- // undermine the cryptographic integrity. |digest| must be exactly
- // |DigestLength()| bytes long.
- [[nodiscard]] bool Verify(base::StringPiece data,
- base::StringPiece digest) const;
- [[nodiscard]] bool Verify(base::span<const uint8_t> data,
- base::span<const uint8_t> digest) const;
- // Verifies a truncated HMAC, behaving identical to Verify(), except
- // that |digest| is allowed to be smaller than |DigestLength()|.
- [[nodiscard]] bool VerifyTruncated(base::StringPiece data,
- base::StringPiece digest) const;
- [[nodiscard]] bool VerifyTruncated(base::span<const uint8_t> data,
- base::span<const uint8_t> digest) const;
- private:
- HashAlgorithm hash_alg_;
- bool initialized_;
- std::vector<unsigned char> key_;
- };
- } // namespace crypto
- #endif // CRYPTO_HMAC_H_
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