1// Copyright (c) 2011 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#include "crypto/hmac.h"
6
7#include <openssl/hmac.h>
8
9#include <algorithm>
10#include <vector>
11
12#include "base/logging.h"
13#include "base/memory/scoped_ptr.h"
14#include "base/stl_util.h"
15#include "crypto/openssl_util.h"
16
17namespace crypto {
18
19struct HMACPlatformData {
20  std::vector<unsigned char> key;
21};
22
23HMAC::HMAC(HashAlgorithm hash_alg)
24    : hash_alg_(hash_alg), plat_(new HMACPlatformData()) {
25  // Only SHA-1 and SHA-256 hash algorithms are supported now.
26  DCHECK(hash_alg_ == SHA1 || hash_alg_ == SHA256);
27}
28
29bool HMAC::Init(const unsigned char* key, size_t key_length) {
30  // Init must not be called more than once on the same HMAC object.
31  DCHECK(plat_->key.empty());
32
33  plat_->key.assign(key, key + key_length);
34  if (key_length == 0) {
35    // Special-case: if the key is empty, use a key with one zero
36    // byte. OpenSSL's HMAC function breaks when passed a NULL key. (It calls
37    // HMAC_Init_ex which treats a NULL key as having already been initialized
38    // with a key previously.) HMAC pads keys with zeros, so this key is
39    // equivalent.
40    plat_->key.push_back(0);
41  }
42  return true;
43}
44
45HMAC::~HMAC() {
46  // Zero out key copy.
47  plat_->key.assign(plat_->key.size(), 0);
48  STLClearObject(&plat_->key);
49}
50
51bool HMAC::Sign(const base::StringPiece& data,
52                unsigned char* digest,
53                size_t digest_length) const {
54  DCHECK(!plat_->key.empty());  // Init must be called before Sign.
55
56  ScopedOpenSSLSafeSizeBuffer<EVP_MAX_MD_SIZE> result(digest, digest_length);
57  return ::HMAC(hash_alg_ == SHA1 ? EVP_sha1() : EVP_sha256(),
58                &plat_->key[0], plat_->key.size(),
59                reinterpret_cast<const unsigned char*>(data.data()),
60                data.size(),
61                result.safe_buffer(), NULL);
62}
63
64}  // namespace crypto
65