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author | agl@chromium.org <agl@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98> | 2012-11-09 19:30:32 +0000 |
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committer | agl@chromium.org <agl@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98> | 2012-11-09 19:30:32 +0000 |
commit | 017105b9700ceb92a5f340cbc789087af43aa585 (patch) | |
tree | 1d91da98dea41d2eeb111c2aec268809c6e2151f /crypto/ghash.h | |
parent | 8619a384c733746c7249fef2e04e84f1a8918ace (diff) | |
download | chromium_src-017105b9700ceb92a5f340cbc789087af43aa585.zip chromium_src-017105b9700ceb92a5f340cbc789087af43aa585.tar.gz chromium_src-017105b9700ceb92a5f340cbc789087af43aa585.tar.bz2 |
crypto: add GHASH implementation.
Can be used to implement GCM until GCM support in NSS is widespread.
Review URL: https://codereview.chromium.org/11175015
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@166952 0039d316-1c4b-4281-b951-d872f2087c98
Diffstat (limited to 'crypto/ghash.h')
-rw-r--r-- | crypto/ghash.h | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/crypto/ghash.h b/crypto/ghash.h new file mode 100644 index 0000000..6dc247b --- /dev/null +++ b/crypto/ghash.h @@ -0,0 +1,86 @@ +// 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. + +#include "base/basictypes.h" +#include "crypto/crypto_export.h" + +namespace crypto { + +// GaloisHash implements the polynomial authenticator part of GCM as specified +// in http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-revised-spec.pdf +// Specifically it implements the GHASH function, defined in section 2.3 of +// that document. +// +// In SP-800-38D, GHASH is defined differently and takes only a single data +// argument. But it is always called with an argument of a certain form: +// GHASH_H (A || 0^v || C || 0^u || [len(A)]_64 || [len(C)]_64) +// This mirrors how the gcm-revised-spec.pdf version of GHASH handles its two +// data arguments. The two GHASH functions therefore differ only in whether the +// data is formatted inside or outside of the function. +// +// WARNING: do not use this as a generic authenticator. Polynomial +// authenticators must be used in the correct manner and any use outside of GCM +// requires careful consideration. +// +// WARNING: this code is not constant time. However, in all likelihood, nor is +// the implementation of AES that is used. +class CRYPTO_EXPORT_PRIVATE GaloisHash { + public: + explicit GaloisHash(const uint8 key[16]); + + // Reset prepares to digest a fresh message with the same key. This is more + // efficient than creating a fresh object. + void Reset(); + + // UpdateAdditional hashes in `additional' data. This is data that is not + // encrypted, but is covered by the authenticator. All additional data must + // be written before any ciphertext is written. + void UpdateAdditional(const uint8* data, size_t length); + + // UpdateCiphertext hashes in ciphertext to be authenticated. + void UpdateCiphertext(const uint8* data, size_t length); + + // Finish completes the hash computation and writes at most |len| bytes of + // the result to |output|. + void Finish(void* output, size_t len); + + private: + enum State { + kHashingAdditionalData, + kHashingCiphertext, + kComplete, + }; + + struct FieldElement { + uint64 low, hi; + }; + + // Add returns |x|+|y|. + static FieldElement Add(const FieldElement& x, const FieldElement& y); + // Double returns 2*|x|. + static FieldElement Double(const FieldElement& x); + // MulAfterPrecomputation sets |x| = |x|*h where h is |table[1]| and + // table[i] = i*h for i=0..15. + static void MulAfterPrecomputation(const FieldElement* table, + FieldElement* x); + // Mul16 sets |x| = 16*|x|. + static void Mul16(FieldElement* x); + + // UpdateBlocks processes |num_blocks| 16-bytes blocks from |bytes|. + void UpdateBlocks(const uint8* bytes, size_t num_blocks); + // Update processes |length| bytes from |bytes| and calls UpdateBlocks on as + // much data as possible. It uses |buf_| to buffer any remaining data and + // always consumes all of |bytes|. + void Update(const uint8* bytes, size_t length); + + FieldElement y_; + State state_; + size_t additional_bytes_; + size_t ciphertext_bytes_; + uint8 buf_[16]; + size_t buf_used_; + FieldElement product_table_[16]; +}; + +} // namespace crypto |