| // 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 SHA1 for the hash algorithm, but this can be extended easily. |
| |
| #ifndef CRYPTO_HMAC_H_ |
| #define CRYPTO_HMAC_H_ |
| |
| #include "base/basictypes.h" |
| #include "base/compiler_specific.h" |
| #include "base/memory/scoped_ptr.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. |
| struct HMACPlatformData; |
| 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(); |
| |
| // 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. |
| bool Init(const unsigned char* key, size_t key_length) WARN_UNUSED_RESULT; |
| |
| // Initializes this instance using |key|. Call Init |
| // only once. It returns false on the second or later calls. |
| bool Init(SymmetricKey* key) WARN_UNUSED_RESULT; |
| |
| // Initializes this instance using |key|. Call Init only once. It returns |
| // false on the second or later calls. |
| bool Init(const base::StringPiece& key) WARN_UNUSED_RESULT { |
| return Init(reinterpret_cast<const unsigned char*>(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. |
| bool Sign(const base::StringPiece& data, unsigned char* digest, |
| size_t digest_length) const WARN_UNUSED_RESULT; |
| |
| // 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. |
| bool Verify(const base::StringPiece& data, |
| const base::StringPiece& digest) const WARN_UNUSED_RESULT; |
| |
| // Verifies a truncated HMAC, behaving identical to Verify(), except |
| // that |digest| is allowed to be smaller than |DigestLength()|. |
| bool VerifyTruncated( |
| const base::StringPiece& data, |
| const base::StringPiece& digest) const WARN_UNUSED_RESULT; |
| |
| private: |
| HashAlgorithm hash_alg_; |
| scoped_ptr<HMACPlatformData> plat_; |
| |
| DISALLOW_COPY_AND_ASSIGN(HMAC); |
| }; |
| |
| } // namespace crypto |
| |
| #endif // CRYPTO_HMAC_H_ |