crypto/symmetric_key_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/symmetric_key.h"
   6
   7 #include <vector>
   8
   9 // TODO(wtc): replace scoped_array by std::vector.
  10 #include "base/memory/scoped_ptr.h"
  11 #include "base/sys_byteorder.h"
  12
  13 namespace crypto {
  14
  15 namespace {
  16
  17 // The following is a non-public Microsoft header documented in MSDN under
  18 // CryptImportKey / CryptExportKey. Following the header is the byte array of
  19 // the actual plaintext key.
  20 struct PlaintextBlobHeader {
  21   BLOBHEADER hdr;
  22   DWORD cbKeySize;
  23 };
  24
  25 // CryptoAPI makes use of three distinct ALG_IDs for AES, rather than just
  26 // CALG_AES (which exists, but depending on the functions you are calling, may
  27 // result in function failure, whereas the subtype would succeed).
  28 ALG_ID GetAESAlgIDForKeySize(size_t key_size_in_bits) {
  29   // Only AES-128/-192/-256 is supported in CryptoAPI.
  30   switch (key_size_in_bits) {
  31     case 128:
  32       return CALG_AES_128;
  33     case 192:
  34       return CALG_AES_192;
  35     case 256:
  36       return CALG_AES_256;
  37     default:
  38       NOTREACHED();
  39       return 0;
  40   }
  41 };
  42
  43 // Imports a raw/plaintext key of |key_size| stored in |*key_data| into a new
  44 // key created for the specified |provider|. |alg| contains the algorithm of
  45 // the key being imported.
  46 // If |key_data| is intended to be used as an HMAC key, then |alg| should be
  47 // CALG_HMAC.
  48 // If successful, returns true and stores the imported key in |*key|.
  49 // TODO(wtc): use this function in hmac_win.cc.
  50 bool ImportRawKey(HCRYPTPROV provider,
  51                   ALG_ID alg,
  52                   const void* key_data, size_t key_size,
  53                   ScopedHCRYPTKEY* key) {
  54   DCHECK_GT(key_size, 0);
  55
  56   DWORD actual_size =
  57       static_cast<DWORD>(sizeof(PlaintextBlobHeader) + key_size);
  58   std::vector<BYTE> tmp_data(actual_size);
  59   BYTE* actual_key = &tmp_data[0];
  60   memcpy(actual_key + sizeof(PlaintextBlobHeader), key_data, key_size);
  61   PlaintextBlobHeader* key_header =
  62       reinterpret_cast<PlaintextBlobHeader*>(actual_key);
  63   memset(key_header, 0, sizeof(PlaintextBlobHeader));
  64
  65   key_header->hdr.bType = PLAINTEXTKEYBLOB;
  66   key_header->hdr.bVersion = CUR_BLOB_VERSION;
  67   key_header->hdr.aiKeyAlg = alg;
  68
  69   key_header->cbKeySize = static_cast<DWORD>(key_size);
  70
  71   HCRYPTKEY unsafe_key = NULL;
  72   DWORD flags = CRYPT_EXPORTABLE;
  73   if (alg == CALG_HMAC) {
  74     // Though it may appear odd that IPSEC and RC2 are being used, this is
  75     // done in accordance with Microsoft's FIPS 140-2 Security Policy for the
  76     // RSA Enhanced Provider, as the approved means of using arbitrary HMAC
  77     // key material.
  78     key_header->hdr.aiKeyAlg = CALG_RC2;
  79     flags |= CRYPT_IPSEC_HMAC_KEY;
  80   }
  81
  82   BOOL ok =
  83       CryptImportKey(provider, actual_key, actual_size, 0, flags, &unsafe_key);
  84
  85   // Clean up the temporary copy of key, regardless of whether it was imported
  86   // sucessfully or not.
  87   SecureZeroMemory(actual_key, actual_size);
  88
  89   if (!ok)
  90     return false;
  91
  92   key->reset(unsafe_key);
  93   return true;
  94 }
  95
  96 // Attempts to generate a random AES key of |key_size_in_bits|. Returns true
  97 // if generation is successful, storing the generated key in |*key| and the
  98 // key provider (CSP) in |*provider|.
  99 bool GenerateAESKey(size_t key_size_in_bits,
 100                     ScopedHCRYPTPROV* provider,
 101                     ScopedHCRYPTKEY* key) {
 102   DCHECK(provider);
 103   DCHECK(key);
 104
 105   ALG_ID alg = GetAESAlgIDForKeySize(key_size_in_bits);
 106   if (alg == 0)
 107     return false;
 108
 109   ScopedHCRYPTPROV safe_provider;
 110   // Note: The only time NULL is safe to be passed as pszContainer is when
 111   // dwFlags contains CRYPT_VERIFYCONTEXT, as all keys generated and/or used
 112   // will be treated as ephemeral keys and not persisted.
 113   BOOL ok = CryptAcquireContext(safe_provider.receive(), NULL, NULL,
 114                                 PROV_RSA_AES, CRYPT_VERIFYCONTEXT);
 115   if (!ok)
 116     return false;
 117
 118   ScopedHCRYPTKEY safe_key;
 119   // In the FIPS 140-2 Security Policy for CAPI on XP/Vista+, Microsoft notes
 120   // that CryptGenKey makes use of the same functionality exposed via
 121   // CryptGenRandom. The reason this is being used, as opposed to
 122   // CryptGenRandom and CryptImportKey is for compliance with the security
 123   // policy
 124   ok = CryptGenKey(safe_provider.get(), alg, CRYPT_EXPORTABLE,
 125                    safe_key.receive());
 126   if (!ok)
 127     return false;
 128
 129   key->swap(safe_key);
 130   provider->swap(safe_provider);
 131
 132   return true;
 133 }
 134
 135 // Returns true if the HMAC key size meets the requirement of FIPS 198
 136 // Section 3.  |alg| is the hash function used in the HMAC.
 137 bool CheckHMACKeySize(size_t key_size_in_bits, ALG_ID alg) {
 138   DWORD hash_size = 0;
 139   switch (alg) {
 140     case CALG_SHA1:
 141       hash_size = 20;
 142       break;
 143     case CALG_SHA_256:
 144       hash_size = 32;
 145       break;
 146     case CALG_SHA_384:
 147       hash_size = 48;
 148       break;
 149     case CALG_SHA_512:
 150       hash_size = 64;
 151       break;
 152   }
 153   if (hash_size == 0)
 154     return false;
 155
 156   // An HMAC key must be >= L/2, where L is the output size of the hash
 157   // function being used.
 158   return (key_size_in_bits >= (hash_size / 2 * 8) &&
 159          (key_size_in_bits % 8) == 0);
 160 }
 161
 162 // Attempts to generate a random, |key_size_in_bits|-long HMAC key, for use
 163 // with the hash function |alg|.
 164 // |key_size_in_bits| must be >= 1/2 the hash size of |alg| for security.
 165 // Returns true if generation is successful, storing the generated key in
 166 // |*key| and the key provider (CSP) in |*provider|.
 167 bool GenerateHMACKey(size_t key_size_in_bits,
 168                      ALG_ID alg,
 169                      ScopedHCRYPTPROV* provider,
 170                      ScopedHCRYPTKEY* key,
 171                      scoped_ptr<BYTE[]>* raw_key) {
 172   DCHECK(provider);
 173   DCHECK(key);
 174   DCHECK(raw_key);
 175
 176   if (!CheckHMACKeySize(key_size_in_bits, alg))
 177     return false;
 178
 179   ScopedHCRYPTPROV safe_provider;
 180   // See comment in GenerateAESKey as to why NULL is acceptable for the
 181   // container name.
 182   BOOL ok = CryptAcquireContext(safe_provider.receive(), NULL, NULL,
 183                                 PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
 184   if (!ok)
 185     return false;
 186
 187   DWORD key_size_in_bytes = static_cast<DWORD>(key_size_in_bits / 8);
 188   scoped_ptr<BYTE[]> random(new BYTE[key_size_in_bytes]);
 189   ok = CryptGenRandom(safe_provider, key_size_in_bytes, random.get());
 190   if (!ok)
 191     return false;
 192
 193   ScopedHCRYPTKEY safe_key;
 194   bool rv = ImportRawKey(safe_provider, CALG_HMAC, random.get(),
 195                          key_size_in_bytes, &safe_key);
 196   if (rv) {
 197     key->swap(safe_key);
 198     provider->swap(safe_provider);
 199     raw_key->swap(random);
 200   }
 201
 202   SecureZeroMemory(random.get(), key_size_in_bytes);
 203   return rv;
 204 }
 205
 206 // Attempts to create an HMAC hash instance using the specified |provider|
 207 // and |key|. The inner hash function will be |hash_alg|. If successful,
 208 // returns true and stores the hash in |*hash|.
 209 // TODO(wtc): use this function in hmac_win.cc.
 210 bool CreateHMACHash(HCRYPTPROV provider,
 211                     HCRYPTKEY key,
 212                     ALG_ID hash_alg,
 213                     ScopedHCRYPTHASH* hash) {
 214   ScopedHCRYPTHASH safe_hash;
 215   BOOL ok = CryptCreateHash(provider, CALG_HMAC, key, 0, safe_hash.receive());
 216   if (!ok)
 217     return false;
 218
 219   HMAC_INFO hmac_info;
 220   memset(&hmac_info, 0, sizeof(hmac_info));
 221   hmac_info.HashAlgid = hash_alg;
 222
 223   ok = CryptSetHashParam(safe_hash, HP_HMAC_INFO,
 224                          reinterpret_cast<const BYTE*>(&hmac_info), 0);
 225   if (!ok)
 226     return false;
 227
 228   hash->swap(safe_hash);
 229   return true;
 230 }
 231
 232 // Computes a block of the derived key using the PBKDF2 function F for the
 233 // specified |block_index| using the PRF |hash|, writing the output to
 234 // |output_buf|.
 235 // |output_buf| must have enough space to accomodate the output of the PRF
 236 // specified by |hash|.
 237 // Returns true if the block was successfully computed.
 238 bool ComputePBKDF2Block(HCRYPTHASH hash,
 239                         DWORD hash_size,
 240                         const std::string& salt,
 241                         size_t iterations,
 242                         uint32 block_index,
 243                         BYTE* output_buf) {
 244   // From RFC 2898:
 245   // 3. <snip> The function F is defined as the exclusive-or sum of the first
 246   //    c iterates of the underlying pseudorandom function PRF applied to the
 247   //    password P and the concatenation of the salt S and the block index i:
 248   //      F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
 249   //    where
 250   //      U_1 = PRF(P, S || INT (i))
 251   //      U_2 = PRF(P, U_1)
 252   //      ...
 253   //      U_c = PRF(P, U_{c-1})
 254   ScopedHCRYPTHASH safe_hash;
 255   BOOL ok = CryptDuplicateHash(hash, NULL, 0, safe_hash.receive());
 256   if (!ok)
 257     return false;
 258
 259   // Iteration U_1: Compute PRF for S.
 260   ok = CryptHashData(safe_hash, reinterpret_cast<const BYTE*>(salt.data()),
 261                      static_cast<DWORD>(salt.size()), 0);
 262   if (!ok)
 263     return false;
 264
 265   // Iteration U_1: and append (big-endian) INT (i).
 266   uint32 big_endian_block_index = base::HostToNet32(block_index);
 267   ok = CryptHashData(safe_hash,
 268                      reinterpret_cast<BYTE*>(&big_endian_block_index),
 269                      sizeof(big_endian_block_index), 0);
 270
 271   std::vector<BYTE> hash_value(hash_size);
 272
 273   DWORD size = hash_size;
 274   ok = CryptGetHashParam(safe_hash, HP_HASHVAL, &hash_value[0], &size, 0);
 275   if (!ok  || size != hash_size)
 276     return false;
 277
 278   memcpy(output_buf, &hash_value[0], hash_size);
 279
 280   // Iteration 2 - c: Compute U_{iteration} by applying the PRF to
 281   // U_{iteration - 1}, then xor the resultant hash with |output|, which
 282   // contains U_1 ^ U_2 ^ ... ^ U_{iteration - 1}.
 283   for (size_t iteration = 2; iteration <= iterations; ++iteration) {
 284     safe_hash.reset();
 285     ok = CryptDuplicateHash(hash, NULL, 0, safe_hash.receive());
 286     if (!ok)
 287       return false;
 288
 289     ok = CryptHashData(safe_hash, &hash_value[0], hash_size, 0);
 290     if (!ok)
 291       return false;
 292
 293     size = hash_size;
 294     ok = CryptGetHashParam(safe_hash, HP_HASHVAL, &hash_value[0], &size, 0);
 295     if (!ok || size != hash_size)
 296       return false;
 297
 298     for (int i = 0; i < hash_size; ++i)
 299       output_buf[i] ^= hash_value[i];
 300   }
 301
 302   return true;
 303 }
 304
 305 }  // namespace
 306
 307 SymmetricKey::~SymmetricKey() {
 308   // TODO(wtc): create a "secure" string type that zeroes itself in the
 309   // destructor.
 310   if (!raw_key_.empty())
 311     SecureZeroMemory(const_cast<char *>(raw_key_.data()), raw_key_.size());
 312 }
 313
 314 // static
 315 SymmetricKey* SymmetricKey::GenerateRandomKey(Algorithm algorithm,
 316                                               size_t key_size_in_bits) {
 317   DCHECK_GE(key_size_in_bits, 8);
 318
 319   ScopedHCRYPTPROV provider;
 320   ScopedHCRYPTKEY key;
 321
 322   bool ok = false;
 323   scoped_ptr<BYTE[]> raw_key;
 324
 325   switch (algorithm) {
 326     case AES:
 327       ok = GenerateAESKey(key_size_in_bits, &provider, &key);
 328       break;
 329     case HMAC_SHA1:
 330       ok = GenerateHMACKey(key_size_in_bits, CALG_SHA1, &provider,
 331                            &key, &raw_key);
 332       break;
 333   }
 334
 335   if (!ok) {
 336     NOTREACHED();
 337     return NULL;
 338   }
 339
 340   size_t key_size_in_bytes = key_size_in_bits / 8;
 341   if (raw_key == NULL)
 342     key_size_in_bytes = 0;
 343
 344   SymmetricKey* result = new SymmetricKey(provider.release(),
 345                                           key.release(),
 346                                           raw_key.get(),
 347                                           key_size_in_bytes);
 348   if (raw_key != NULL)
 349     SecureZeroMemory(raw_key.get(), key_size_in_bytes);
 350
 351   return result;
 352 }
 353
 354 // static
 355 SymmetricKey* SymmetricKey::DeriveKeyFromPassword(Algorithm algorithm,
 356                                                   const std::string& password,
 357                                                   const std::string& salt,
 358                                                   size_t iterations,
 359                                                   size_t key_size_in_bits) {
 360   // CryptoAPI lacks routines to perform PBKDF2 derivation as specified
 361   // in RFC 2898, so it must be manually implemented. Only HMAC-SHA1 is
 362   // supported as the PRF.
 363
 364   // While not used until the end, sanity-check the input before proceeding
 365   // with the expensive computation.
 366   DWORD provider_type = 0;
 367   ALG_ID alg = 0;
 368   switch (algorithm) {
 369     case AES:
 370       provider_type = PROV_RSA_AES;
 371       alg = GetAESAlgIDForKeySize(key_size_in_bits);
 372       break;
 373     case HMAC_SHA1:
 374       provider_type = PROV_RSA_FULL;
 375       alg = CALG_HMAC;
 376       break;
 377     default:
 378       NOTREACHED();
 379       break;
 380   }
 381   if (provider_type == 0 || alg == 0)
 382     return NULL;
 383
 384   ScopedHCRYPTPROV provider;
 385   BOOL ok = CryptAcquireContext(provider.receive(), NULL, NULL, provider_type,
 386                                 CRYPT_VERIFYCONTEXT);
 387   if (!ok)
 388     return NULL;
 389
 390   // Convert the user password into a key suitable to be fed into the PRF
 391   // function.
 392   ScopedHCRYPTKEY password_as_key;
 393   BYTE* password_as_bytes =
 394       const_cast<BYTE*>(reinterpret_cast<const BYTE*>(password.data()));
 395   if (!ImportRawKey(provider, CALG_HMAC, password_as_bytes,
 396                     password.size(), &password_as_key))
 397     return NULL;
 398
 399   // Configure the PRF function. Only HMAC variants are supported, with the
 400   // only hash function supported being SHA1.
 401   // TODO(rsleevi): Support SHA-256 on XP SP3+.
 402   ScopedHCRYPTHASH prf;
 403   if (!CreateHMACHash(provider, password_as_key, CALG_SHA1, &prf))
 404     return NULL;
 405
 406   DWORD hLen = 0;
 407   DWORD param_size = sizeof(hLen);
 408   ok = CryptGetHashParam(prf, HP_HASHSIZE,
 409                          reinterpret_cast<BYTE*>(&hLen), &param_size, 0);
 410   if (!ok || hLen == 0)
 411     return NULL;
 412
 413   // 1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and stop.
 414   size_t dkLen = key_size_in_bits / 8;
 415   DCHECK_GT(dkLen, 0);
 416
 417   if ((dkLen / hLen) > 0xFFFFFFFF) {
 418     DLOG(ERROR) << "Derived key too long.";
 419     return NULL;
 420   }
 421
 422   // 2. Let l be the number of hLen-octet blocks in the derived key,
 423   //    rounding up, and let r be the number of octets in the last
 424   //    block:
 425   size_t L = (dkLen + hLen - 1) / hLen;
 426   DCHECK_GT(L, 0);
 427
 428   size_t total_generated_size = L * hLen;
 429   std::vector<BYTE> generated_key(total_generated_size);
 430   BYTE* block_offset = &generated_key[0];
 431
 432   // 3. For each block of the derived key apply the function F defined below
 433   //    to the password P, the salt S, the iteration count c, and the block
 434   //    index to compute the block:
 435   //    T_1 = F (P, S, c, 1)
 436   //    T_2 = F (P, S, c, 2)
 437   //    ...
 438   //    T_l = F (P, S, c, l)
 439   // <snip>
 440   // 4. Concatenate the blocks and extract the first dkLen octets to produce
 441   //    a derived key DK:
 442   //    DK = T_1 || T_2 || ... || T_l<0..r-1>
 443   for (uint32 block_index = 1; block_index <= L; ++block_index) {
 444     if (!ComputePBKDF2Block(prf, hLen, salt, iterations, block_index,
 445                             block_offset))
 446         return NULL;
 447     block_offset += hLen;
 448   }
 449
 450   // Convert the derived key bytes into a key handle for the desired algorithm.
 451   ScopedHCRYPTKEY key;
 452   if (!ImportRawKey(provider, alg, &generated_key[0], dkLen, &key))
 453     return NULL;
 454
 455   SymmetricKey* result = new SymmetricKey(provider.release(), key.release(),
 456                                           &generated_key[0], dkLen);
 457
 458   SecureZeroMemory(&generated_key[0], total_generated_size);
 459
 460   return result;
 461 }
 462
 463 // static
 464 SymmetricKey* SymmetricKey::Import(Algorithm algorithm,
 465                                    const std::string& raw_key) {
 466   DWORD provider_type = 0;
 467   ALG_ID alg = 0;
 468   switch (algorithm) {
 469     case AES:
 470       provider_type = PROV_RSA_AES;
 471       alg = GetAESAlgIDForKeySize(raw_key.size() * 8);
 472       break;
 473     case HMAC_SHA1:
 474       provider_type = PROV_RSA_FULL;
 475       alg = CALG_HMAC;
 476       break;
 477     default:
 478       NOTREACHED();
 479       break;
 480   }
 481   if (provider_type == 0 || alg == 0)
 482     return NULL;
 483
 484   ScopedHCRYPTPROV provider;
 485   BOOL ok = CryptAcquireContext(provider.receive(), NULL, NULL, provider_type,
 486                                 CRYPT_VERIFYCONTEXT);
 487   if (!ok)
 488     return NULL;
 489
 490   ScopedHCRYPTKEY key;
 491   if (!ImportRawKey(provider, alg, raw_key.data(), raw_key.size(), &key))
 492     return NULL;
 493
 494   return new SymmetricKey(provider.release(), key.release(),
 495                           raw_key.data(), raw_key.size());
 496 }
 497
 498 bool SymmetricKey::GetRawKey(std::string* raw_key) {
 499   // Short circuit for when the key was supplied to the constructor.
 500   if (!raw_key_.empty()) {
 501     *raw_key = raw_key_;
 502     return true;
 503   }
 504
 505   DWORD size = 0;
 506   BOOL ok = CryptExportKey(key_, 0, PLAINTEXTKEYBLOB, 0, NULL, &size);
 507   if (!ok)
 508     return false;
 509
 510   std::vector<BYTE> result(size);
 511
 512   ok = CryptExportKey(key_, 0, PLAINTEXTKEYBLOB, 0, &result[0], &size);
 513   if (!ok)
 514     return false;
 515
 516   PlaintextBlobHeader* header =
 517       reinterpret_cast<PlaintextBlobHeader*>(&result[0]);
 518   raw_key->assign(reinterpret_cast<char*>(&result[sizeof(*header)]),
 519                   header->cbKeySize);
 520
 521   SecureZeroMemory(&result[0], size);
 522
 523   return true;
 524 }
 525
 526 SymmetricKey::SymmetricKey(HCRYPTPROV provider,
 527                            HCRYPTKEY key,
 528                            const void* key_data, size_t key_size_in_bytes)
 529     : provider_(provider), key_(key) {
 530   if (key_data) {
 531     raw_key_.assign(reinterpret_cast<const char*>(key_data),
 532                     key_size_in_bytes);
 533   }
 534 }
 535
 536 }  // namespace crypto