crypto/hmac_win.cc

   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 <windows.h>
   8 #include <wincrypt.h>
   9
  10 #include <algorithm>
  11 #include <vector>
  12
  13 #include "base/logging.h"
  14 #include "crypto/scoped_capi_types.h"
  15 #include "crypto/third_party/nss/blapi.h"
  16 #include "crypto/third_party/nss/sha256.h"
  17
  18 namespace crypto {
  19
  20 namespace {
  21
  22 // Implementation of HMAC-SHA-256:
  23 //
  24 // SHA-256 is supported in Windows XP SP3 or later.  We still need to support
  25 // Windows XP SP2, so unfortunately we have to implement HMAC-SHA-256 here.
  26
  27 enum {
  28   SHA256_BLOCK_SIZE = 64  // Block size (in bytes) of the input to SHA-256.
  29 };
  30
  31 // See FIPS 198: The Keyed-Hash Message Authentication Code (HMAC).
  32 void ComputeHMACSHA256(const unsigned char* key, size_t key_len,
  33                        const unsigned char* text, size_t text_len,
  34                        unsigned char* output, size_t output_len) {
  35   SHA256Context ctx;
  36
  37   // Pre-process the key, if necessary.
  38   unsigned char key0[SHA256_BLOCK_SIZE];
  39   if (key_len > SHA256_BLOCK_SIZE) {
  40     SHA256_Begin(&ctx);
  41     SHA256_Update(&ctx, key, key_len);
  42     SHA256_End(&ctx, key0, NULL, SHA256_LENGTH);
  43     memset(key0 + SHA256_LENGTH, 0, SHA256_BLOCK_SIZE - SHA256_LENGTH);
  44   } else {
  45     memcpy(key0, key, key_len);
  46     memset(key0 + key_len, 0, SHA256_BLOCK_SIZE - key_len);
  47   }
  48
  49   unsigned char padded_key[SHA256_BLOCK_SIZE];
  50   unsigned char inner_hash[SHA256_LENGTH];
  51
  52   // XOR key0 with ipad.
  53   for (int i = 0; i < SHA256_BLOCK_SIZE; ++i)
  54     padded_key[i] = key0[i] ^ 0x36;
  55
  56   // Compute the inner hash.
  57   SHA256_Begin(&ctx);
  58   SHA256_Update(&ctx, padded_key, SHA256_BLOCK_SIZE);
  59   SHA256_Update(&ctx, text, text_len);
  60   SHA256_End(&ctx, inner_hash, NULL, SHA256_LENGTH);
  61
  62   // XOR key0 with opad.
  63   for (int i = 0; i < SHA256_BLOCK_SIZE; ++i)
  64     padded_key[i] = key0[i] ^ 0x5c;
  65
  66   // Compute the outer hash.
  67   SHA256_Begin(&ctx);
  68   SHA256_Update(&ctx, padded_key, SHA256_BLOCK_SIZE);
  69   SHA256_Update(&ctx, inner_hash, SHA256_LENGTH);
  70   SHA256_End(&ctx, output, NULL, output_len);
  71 }
  72
  73 }  // namespace
  74
  75 struct HMACPlatformData {
  76   ~HMACPlatformData() {
  77     if (!raw_key_.empty()) {
  78       SecureZeroMemory(&raw_key_[0], raw_key_.size());
  79     }
  80
  81     // Destroy the key before releasing the provider.
  82     key_.reset();
  83   }
  84
  85   ScopedHCRYPTPROV provider_;
  86   ScopedHCRYPTKEY key_;
  87
  88   // For HMAC-SHA-256 only.
  89   std::vector<unsigned char> raw_key_;
  90 };
  91
  92 HMAC::HMAC(HashAlgorithm hash_alg)
  93     : hash_alg_(hash_alg), plat_(new HMACPlatformData()) {
  94   // Only SHA-1 and SHA-256 hash algorithms are supported now.
  95   DCHECK(hash_alg_ == SHA1 || hash_alg_ == SHA256);
  96 }
  97
  98 bool HMAC::Init(const unsigned char* key, int key_length) {
  99   if (plat_->provider_ || plat_->key_ || !plat_->raw_key_.empty()) {
 100     // Init must not be called more than once on the same HMAC object.
 101     NOTREACHED();
 102     return false;
 103   }
 104
 105   if (hash_alg_ == SHA256) {
 106     if (key_length < SHA256_LENGTH / 2)
 107       return false;  // Key is too short.
 108     plat_->raw_key_.assign(key, key + key_length);
 109     return true;
 110   }
 111
 112   if (!CryptAcquireContext(plat_->provider_.receive(), NULL, NULL,
 113                            PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) {
 114     NOTREACHED();
 115     return false;
 116   }
 117
 118   // This code doesn't work on Win2k because PLAINTEXTKEYBLOB and
 119   // CRYPT_IPSEC_HMAC_KEY are not supported on Windows 2000.  PLAINTEXTKEYBLOB
 120   // allows the import of an unencrypted key.  For Win2k support, a cubmbersome
 121   // exponent-of-one key procedure must be used:
 122   //     http://support.microsoft.com/kb/228786/en-us
 123   // CRYPT_IPSEC_HMAC_KEY allows keys longer than 16 bytes.
 124
 125   struct KeyBlob {
 126     BLOBHEADER header;
 127     DWORD key_size;
 128     BYTE key_data[1];
 129   };
 130   size_t key_blob_size = std::max(offsetof(KeyBlob, key_data) + key_length,
 131                                   sizeof(KeyBlob));
 132   std::vector<BYTE> key_blob_storage = std::vector<BYTE>(key_blob_size);
 133   KeyBlob* key_blob = reinterpret_cast<KeyBlob*>(&key_blob_storage[0]);
 134   key_blob->header.bType = PLAINTEXTKEYBLOB;
 135   key_blob->header.bVersion = CUR_BLOB_VERSION;
 136   key_blob->header.reserved = 0;
 137   key_blob->header.aiKeyAlg = CALG_RC2;
 138   key_blob->key_size = key_length;
 139   memcpy(key_blob->key_data, key, key_length);
 140
 141   if (!CryptImportKey(plat_->provider_, &key_blob_storage[0],
 142                       key_blob_storage.size(), 0, CRYPT_IPSEC_HMAC_KEY,
 143                       plat_->key_.receive())) {
 144     NOTREACHED();
 145     return false;
 146   }
 147
 148   // Destroy the copy of the key.
 149   SecureZeroMemory(key_blob->key_data, key_length);
 150
 151   return true;
 152 }
 153
 154 HMAC::~HMAC() {
 155 }
 156
 157 bool HMAC::Sign(const base::StringPiece& data,
 158                 unsigned char* digest,
 159                 int digest_length) const {
 160   if (hash_alg_ == SHA256) {
 161     if (plat_->raw_key_.empty())
 162       return false;
 163     ComputeHMACSHA256(&plat_->raw_key_[0], plat_->raw_key_.size(),
 164                       reinterpret_cast<const unsigned char*>(data.data()),
 165                       data.size(), digest, digest_length);
 166     return true;
 167   }
 168
 169   if (!plat_->provider_ || !plat_->key_)
 170     return false;
 171
 172   if (hash_alg_ != SHA1) {
 173     NOTREACHED();
 174     return false;
 175   }
 176
 177   ScopedHCRYPTHASH hash;
 178   if (!CryptCreateHash(plat_->provider_, CALG_HMAC, plat_->key_, 0,
 179                        hash.receive()))
 180     return false;
 181
 182   HMAC_INFO hmac_info;
 183   memset(&hmac_info, 0, sizeof(hmac_info));
 184   hmac_info.HashAlgid = CALG_SHA1;
 185   if (!CryptSetHashParam(hash, HP_HMAC_INFO,
 186                          reinterpret_cast<BYTE*>(&hmac_info), 0))
 187     return false;
 188
 189   if (!CryptHashData(hash, reinterpret_cast<const BYTE*>(data.data()),
 190                      static_cast<DWORD>(data.size()), 0))
 191     return false;
 192
 193   DWORD sha1_size = digest_length;
 194   return !!CryptGetHashParam(hash, HP_HASHVAL, digest, &sha1_size, 0);
 195 }
 196
 197 }  // namespace crypto