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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 <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/chromium-blapi.h"
     16 #include "crypto/third_party/nss/chromium-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 // 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
    210