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      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 #include "crypto/hmac.h"
      6 
      7 #include <stddef.h>
      8 
      9 #include <algorithm>
     10 #include <string>
     11 
     12 #include "base/logging.h"
     13 #include "base/stl_util.h"
     14 #include "crypto/openssl_util.h"
     15 #include "crypto/secure_util.h"
     16 #include "crypto/symmetric_key.h"
     17 #include "third_party/boringssl/src/include/openssl/hmac.h"
     18 
     19 namespace crypto {
     20 
     21 HMAC::HMAC(HashAlgorithm hash_alg) : hash_alg_(hash_alg), initialized_(false) {
     22   // Only SHA-1 and SHA-256 hash algorithms are supported now.
     23   DCHECK(hash_alg_ == SHA1 || hash_alg_ == SHA256);
     24 }
     25 
     26 HMAC::~HMAC() {
     27   // Zero out key copy.
     28   key_.assign(key_.size(), 0);
     29   base::STLClearObject(&key_);
     30 }
     31 
     32 size_t HMAC::DigestLength() const {
     33   switch (hash_alg_) {
     34     case SHA1:
     35       return 20;
     36     case SHA256:
     37       return 32;
     38     default:
     39       NOTREACHED();
     40       return 0;
     41   }
     42 }
     43 
     44 bool HMAC::Init(const unsigned char* key, size_t key_length) {
     45   // Init must not be called more than once on the same HMAC object.
     46   DCHECK(!initialized_);
     47   initialized_ = true;
     48   key_.assign(key, key + key_length);
     49   return true;
     50 }
     51 
     52 bool HMAC::Init(const SymmetricKey* key) {
     53   return Init(key->key());
     54 }
     55 
     56 bool HMAC::Sign(base::StringPiece data,
     57                 unsigned char* digest,
     58                 size_t digest_length) const {
     59   DCHECK(initialized_);
     60 
     61   ScopedOpenSSLSafeSizeBuffer<EVP_MAX_MD_SIZE> result(digest, digest_length);
     62   return !!::HMAC(hash_alg_ == SHA1 ? EVP_sha1() : EVP_sha256(), key_.data(),
     63                   key_.size(),
     64                   reinterpret_cast<const unsigned char*>(data.data()),
     65                   data.size(), result.safe_buffer(), nullptr);
     66 }
     67 
     68 bool HMAC::Verify(base::StringPiece data, base::StringPiece digest) const {
     69   if (digest.size() != DigestLength())
     70     return false;
     71   return VerifyTruncated(data, digest);
     72 }
     73 
     74 bool HMAC::VerifyTruncated(base::StringPiece data,
     75                            base::StringPiece digest) const {
     76   if (digest.empty())
     77     return false;
     78   size_t digest_length = DigestLength();
     79   std::unique_ptr<unsigned char[]> computed_digest(
     80       new unsigned char[digest_length]);
     81   if (!Sign(data, computed_digest.get(), digest_length))
     82     return false;
     83 
     84   return SecureMemEqual(digest.data(), computed_digest.get(),
     85                         std::min(digest.size(), digest_length));
     86 }
     87 
     88 }  // namespace crypto
     89