1 // Copyright (c) 2012 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 // Utility class for calculating the HMAC for a given message. We currently 6 // only support SHA1 for the hash algorithm, but this can be extended easily. 7 8 #ifndef CRYPTO_HMAC_H_ 9 #define CRYPTO_HMAC_H_ 10 11 #include <stddef.h> 12 13 #include "base/compiler_specific.h" 14 #include "base/macros.h" 15 #include "base/memory/scoped_ptr.h" 16 #include "base/strings/string_piece.h" 17 #include "crypto/crypto_export.h" 18 19 namespace crypto { 20 21 // Simplify the interface and reduce includes by abstracting out the internals. 22 struct HMACPlatformData; 23 class SymmetricKey; 24 25 class CRYPTO_EXPORT HMAC { 26 public: 27 // The set of supported hash functions. Extend as required. 28 enum HashAlgorithm { 29 SHA1, 30 SHA256, 31 }; 32 33 explicit HMAC(HashAlgorithm hash_alg); 34 ~HMAC(); 35 36 // Returns the length of digest that this HMAC will create. 37 size_t DigestLength() const; 38 39 // TODO(abarth): Add a PreferredKeyLength() member function. 40 41 // Initializes this instance using |key| of the length |key_length|. Call Init 42 // only once. It returns false on the second or later calls. 43 // 44 // NOTE: the US Federal crypto standard FIPS 198, Section 3 says: 45 // The size of the key, K, shall be equal to or greater than L/2, where L 46 // is the size of the hash function output. 47 // In FIPS 198-1 (and SP-800-107, which describes key size recommendations), 48 // this requirement is gone. But a system crypto library may still enforce 49 // this old requirement. If the key is shorter than this recommended value, 50 // Init() may fail. 51 bool Init(const unsigned char* key, size_t key_length) WARN_UNUSED_RESULT; 52 53 // Initializes this instance using |key|. Call Init 54 // only once. It returns false on the second or later calls. 55 bool Init(SymmetricKey* key) WARN_UNUSED_RESULT; 56 57 // Initializes this instance using |key|. Call Init only once. It returns 58 // false on the second or later calls. Init(const base::StringPiece & key)59 bool Init(const base::StringPiece& key) WARN_UNUSED_RESULT { 60 return Init(reinterpret_cast<const unsigned char*>(key.data()), 61 key.size()); 62 } 63 64 // Calculates the HMAC for the message in |data| using the algorithm supplied 65 // to the constructor and the key supplied to the Init method. The HMAC is 66 // returned in |digest|, which has |digest_length| bytes of storage available. 67 bool Sign(const base::StringPiece& data, unsigned char* digest, 68 size_t digest_length) const WARN_UNUSED_RESULT; 69 70 // Verifies that the HMAC for the message in |data| equals the HMAC provided 71 // in |digest|, using the algorithm supplied to the constructor and the key 72 // supplied to the Init method. Use of this method is strongly recommended 73 // over using Sign() with a manual comparison (such as memcmp), as such 74 // comparisons may result in side-channel disclosures, such as timing, that 75 // undermine the cryptographic integrity. |digest| must be exactly 76 // |DigestLength()| bytes long. 77 bool Verify(const base::StringPiece& data, 78 const base::StringPiece& digest) const WARN_UNUSED_RESULT; 79 80 // Verifies a truncated HMAC, behaving identical to Verify(), except 81 // that |digest| is allowed to be smaller than |DigestLength()|. 82 bool VerifyTruncated( 83 const base::StringPiece& data, 84 const base::StringPiece& digest) const WARN_UNUSED_RESULT; 85 86 private: 87 HashAlgorithm hash_alg_; 88 scoped_ptr<HMACPlatformData> plat_; 89 90 DISALLOW_COPY_AND_ASSIGN(HMAC); 91 }; 92 93 } // namespace crypto 94 95 #endif // CRYPTO_HMAC_H_ 96