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