crypto/hmac_win.cc

   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 <windows.h>
   8
   9 #include <algorithm>
  10 #include <vector>
  11
  12 #include "base/logging.h"
  13 #include "crypto/scoped_capi_types.h"
  14 #include "crypto/third_party/nss/chromium-blapi.h"
  15 #include "crypto/third_party/nss/chromium-sha256.h"
  16 #include "crypto/wincrypt_shim.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 // NSS doesn't accept size_t for text size, divide the data into smaller
  32 // chunks as needed.
  33 void Wrapped_SHA256_Update(SHA256Context* ctx, const unsigned char* text,
  34                            size_t text_len) {
  35   const unsigned int kChunkSize = 1 << 30;
  36   while (text_len > kChunkSize) {
  37     SHA256_Update(ctx, text, kChunkSize);
  38     text += kChunkSize;
  39     text_len -= kChunkSize;
  40   }
  41   SHA256_Update(ctx, text, (unsigned int)text_len);
  42 }
  43
  44 // See FIPS 198: The Keyed-Hash Message Authentication Code (HMAC).
  45 void ComputeHMACSHA256(const unsigned char* key, size_t key_len,
  46                        const unsigned char* text, size_t text_len,
  47                        unsigned char* output, size_t output_len) {
  48   SHA256Context ctx;
  49
  50   // Pre-process the key, if necessary.
  51   unsigned char key0[SHA256_BLOCK_SIZE];
  52   if (key_len > SHA256_BLOCK_SIZE) {
  53     SHA256_Begin(&ctx);
  54     Wrapped_SHA256_Update(&ctx, key, key_len);
  55     SHA256_End(&ctx, key0, NULL, SHA256_LENGTH);
  56     memset(key0 + SHA256_LENGTH, 0, SHA256_BLOCK_SIZE - SHA256_LENGTH);
  57   } else {
  58     memcpy(key0, key, key_len);
  59     if (key_len < SHA256_BLOCK_SIZE)
  60       memset(key0 + key_len, 0, SHA256_BLOCK_SIZE - key_len);
  61   }
  62
  63   unsigned char padded_key[SHA256_BLOCK_SIZE];
  64   unsigned char inner_hash[SHA256_LENGTH];
  65
  66   // XOR key0 with ipad.
  67   for (int i = 0; i < SHA256_BLOCK_SIZE; ++i)
  68     padded_key[i] = key0[i] ^ 0x36;
  69
  70   // Compute the inner hash.
  71   SHA256_Begin(&ctx);
  72   SHA256_Update(&ctx, padded_key, SHA256_BLOCK_SIZE);
  73   Wrapped_SHA256_Update(&ctx, text, text_len);
  74   SHA256_End(&ctx, inner_hash, NULL, SHA256_LENGTH);
  75
  76   // XOR key0 with opad.
  77   for (int i = 0; i < SHA256_BLOCK_SIZE; ++i)
  78     padded_key[i] = key0[i] ^ 0x5c;
  79
  80   // Compute the outer hash.
  81   SHA256_Begin(&ctx);
  82   SHA256_Update(&ctx, padded_key, SHA256_BLOCK_SIZE);
  83   SHA256_Update(&ctx, inner_hash, SHA256_LENGTH);
  84   SHA256_End(&ctx, output, NULL, (unsigned int) output_len);
  85 }
  86
  87 }  // namespace
  88
  89 struct HMACPlatformData {
  90   ~HMACPlatformData() {
  91     if (!raw_key_.empty()) {
  92       SecureZeroMemory(&raw_key_[0], raw_key_.size());
  93     }
  94
  95     // Destroy the key before releasing the provider.
  96     key_.reset();
  97   }
  98
  99   ScopedHCRYPTPROV provider_;
 100   ScopedHCRYPTKEY key_;
 101
 102   // For HMAC-SHA-256 only.
 103   std::vector<unsigned char> raw_key_;
 104 };
 105
 106 HMAC::HMAC(HashAlgorithm hash_alg)
 107     : hash_alg_(hash_alg), plat_(new HMACPlatformData()) {
 108   // Only SHA-1 and SHA-256 hash algorithms are supported now.
 109   DCHECK(hash_alg_ == SHA1 || hash_alg_ == SHA256);
 110 }
 111
 112 bool HMAC::Init(const unsigned char* key, size_t key_length) {
 113   if (plat_->provider_ || plat_->key_ || !plat_->raw_key_.empty()) {
 114     // Init must not be called more than once on the same HMAC object.
 115     NOTREACHED();
 116     return false;
 117   }
 118
 119   if (hash_alg_ == SHA256) {
 120     plat_->raw_key_.assign(key, key + key_length);
 121     return true;
 122   }
 123
 124   if (!CryptAcquireContext(plat_->provider_.receive(), NULL, NULL,
 125                            PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) {
 126     NOTREACHED();
 127     return false;
 128   }
 129
 130   // This code doesn't work on Win2k because PLAINTEXTKEYBLOB and
 131   // CRYPT_IPSEC_HMAC_KEY are not supported on Windows 2000.  PLAINTEXTKEYBLOB
 132   // allows the import of an unencrypted key.  For Win2k support, a cubmbersome
 133   // exponent-of-one key procedure must be used:
 134   //     http://support.microsoft.com/kb/228786/en-us
 135   // CRYPT_IPSEC_HMAC_KEY allows keys longer than 16 bytes.
 136
 137   struct KeyBlob {
 138     BLOBHEADER header;
 139     DWORD key_size;
 140     BYTE key_data[1];
 141   };
 142   size_t key_blob_size = std::max(offsetof(KeyBlob, key_data) + key_length,
 143                                   sizeof(KeyBlob));
 144   std::vector<BYTE> key_blob_storage = std::vector<BYTE>(key_blob_size);
 145   KeyBlob* key_blob = reinterpret_cast<KeyBlob*>(&key_blob_storage[0]);
 146   key_blob->header.bType = PLAINTEXTKEYBLOB;
 147   key_blob->header.bVersion = CUR_BLOB_VERSION;
 148   key_blob->header.reserved = 0;
 149   key_blob->header.aiKeyAlg = CALG_RC2;
 150   key_blob->key_size = static_cast<DWORD>(key_length);
 151   memcpy(key_blob->key_data, key, key_length);
 152
 153   if (!CryptImportKey(plat_->provider_, &key_blob_storage[0],
 154                       (DWORD)key_blob_storage.size(), 0,
 155                       CRYPT_IPSEC_HMAC_KEY, plat_->key_.receive())) {
 156     NOTREACHED();
 157     return false;
 158   }
 159
 160   // Destroy the copy of the key.
 161   SecureZeroMemory(key_blob->key_data, key_length);
 162
 163   return true;
 164 }
 165
 166 HMAC::~HMAC() {
 167 }
 168
 169 bool HMAC::Sign(const base::StringPiece& data,
 170                 unsigned char* digest,
 171                 size_t digest_length) const {
 172   if (hash_alg_ == SHA256) {
 173     if (plat_->raw_key_.empty())
 174       return false;
 175     ComputeHMACSHA256(&plat_->raw_key_[0], plat_->raw_key_.size(),
 176                       reinterpret_cast<const unsigned char*>(data.data()),
 177                       data.size(), digest, digest_length);
 178     return true;
 179   }
 180
 181   if (!plat_->provider_ || !plat_->key_)
 182     return false;
 183
 184   if (hash_alg_ != SHA1) {
 185     NOTREACHED();
 186     return false;
 187   }
 188
 189   ScopedHCRYPTHASH hash;
 190   if (!CryptCreateHash(plat_->provider_, CALG_HMAC, plat_->key_, 0,
 191                        hash.receive()))
 192     return false;
 193
 194   HMAC_INFO hmac_info;
 195   memset(&hmac_info, 0, sizeof(hmac_info));
 196   hmac_info.HashAlgid = CALG_SHA1;
 197   if (!CryptSetHashParam(hash, HP_HMAC_INFO,
 198                          reinterpret_cast<BYTE*>(&hmac_info), 0))
 199     return false;
 200
 201   if (!CryptHashData(hash, reinterpret_cast<const BYTE*>(data.data()),
 202                      static_cast<DWORD>(data.size()), 0))
 203     return false;
 204
 205   DWORD sha1_size = static_cast<DWORD>(digest_length);
 206   return !!CryptGetHashParam(hash, HP_HASHVAL, digest, &sha1_size, 0);
 207 }
 208
 209 }  // namespace crypto