1 /* $OpenBSD: s3_cbc.c,v 1.22 2020/06/19 21:26:40 tb Exp $ */ 2 /* ==================================================================== 3 * Copyright (c) 2012 The OpenSSL Project. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in 14 * the documentation and/or other materials provided with the 15 * distribution. 16 * 17 * 3. All advertising materials mentioning features or use of this 18 * software must display the following acknowledgment: 19 * "This product includes software developed by the OpenSSL Project 20 * for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 21 * 22 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 23 * endorse or promote products derived from this software without 24 * prior written permission. For written permission, please contact 25 * openssl-core@openssl.org. 26 * 27 * 5. Products derived from this software may not be called "OpenSSL" 28 * nor may "OpenSSL" appear in their names without prior written 29 * permission of the OpenSSL Project. 30 * 31 * 6. Redistributions of any form whatsoever must retain the following 32 * acknowledgment: 33 * "This product includes software developed by the OpenSSL Project 34 * for use in the OpenSSL Toolkit (http://www.openssl.org/)" 35 * 36 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 37 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 38 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 39 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 40 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 41 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 42 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 43 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 44 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 45 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 46 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 47 * OF THE POSSIBILITY OF SUCH DAMAGE. 48 * ==================================================================== 49 * 50 * This product includes cryptographic software written by Eric Young 51 * (eay@cryptsoft.com). This product includes software written by Tim 52 * Hudson (tjh@cryptsoft.com). 53 * 54 */ 55 56 #include "ssl_locl.h" 57 58 #include <openssl/md5.h> 59 #include <openssl/sha.h> 60 61 /* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length 62 * field. (SHA-384/512 have 128-bit length.) */ 63 #define MAX_HASH_BIT_COUNT_BYTES 16 64 65 /* MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support. 66 * Currently SHA-384/512 has a 128-byte block size and that's the largest 67 * supported by TLS.) */ 68 #define MAX_HASH_BLOCK_SIZE 128 69 70 /* Some utility functions are needed: 71 * 72 * These macros return the given value with the MSB copied to all the other 73 * bits. They use the fact that arithmetic shift shifts-in the sign bit. 74 * However, this is not ensured by the C standard so you may need to replace 75 * them with something else on odd CPUs. */ 76 #define DUPLICATE_MSB_TO_ALL(x) ((unsigned int)((int)(x) >> (sizeof(int) * 8 - 1))) 77 #define DUPLICATE_MSB_TO_ALL_8(x) ((unsigned char)(DUPLICATE_MSB_TO_ALL(x))) 78 79 /* constant_time_lt returns 0xff if a<b and 0x00 otherwise. */ 80 static unsigned int 81 constant_time_lt(unsigned int a, unsigned int b) 82 { 83 a -= b; 84 return DUPLICATE_MSB_TO_ALL(a); 85 } 86 87 /* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */ 88 static unsigned int 89 constant_time_ge(unsigned int a, unsigned int b) 90 { 91 a -= b; 92 return DUPLICATE_MSB_TO_ALL(~a); 93 } 94 95 /* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */ 96 static unsigned char 97 constant_time_eq_8(unsigned int a, unsigned int b) 98 { 99 unsigned int c = a ^ b; 100 c--; 101 return DUPLICATE_MSB_TO_ALL_8(c); 102 } 103 104 /* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC 105 * record in |rec| in constant time and returns 1 if the padding is valid and 106 * -1 otherwise. It also removes any explicit IV from the start of the record 107 * without leaking any timing about whether there was enough space after the 108 * padding was removed. 109 * 110 * block_size: the block size of the cipher used to encrypt the record. 111 * returns: 112 * 0: (in non-constant time) if the record is publicly invalid. 113 * 1: if the padding was valid 114 * -1: otherwise. */ 115 int 116 tls1_cbc_remove_padding(const SSL* s, SSL3_RECORD_INTERNAL *rec, 117 unsigned int block_size, unsigned int mac_size) 118 { 119 unsigned int padding_length, good, to_check, i; 120 const unsigned int overhead = 1 /* padding length byte */ + mac_size; 121 122 /* Check if version requires explicit IV */ 123 if (SSL_USE_EXPLICIT_IV(s)) { 124 /* These lengths are all public so we can test them in 125 * non-constant time. 126 */ 127 if (overhead + block_size > rec->length) 128 return 0; 129 /* We can now safely skip explicit IV */ 130 rec->data += block_size; 131 rec->input += block_size; 132 rec->length -= block_size; 133 } else if (overhead > rec->length) 134 return 0; 135 136 padding_length = rec->data[rec->length - 1]; 137 138 good = constant_time_ge(rec->length, overhead + padding_length); 139 /* The padding consists of a length byte at the end of the record and 140 * then that many bytes of padding, all with the same value as the 141 * length byte. Thus, with the length byte included, there are i+1 142 * bytes of padding. 143 * 144 * We can't check just |padding_length+1| bytes because that leaks 145 * decrypted information. Therefore we always have to check the maximum 146 * amount of padding possible. (Again, the length of the record is 147 * public information so we can use it.) */ 148 to_check = 256; /* maximum amount of padding, inc length byte. */ 149 if (to_check > rec->length) 150 to_check = rec->length; 151 152 for (i = 0; i < to_check; i++) { 153 unsigned char mask = constant_time_ge(padding_length, i); 154 unsigned char b = rec->data[rec->length - 1 - i]; 155 /* The final |padding_length+1| bytes should all have the value 156 * |padding_length|. Therefore the XOR should be zero. */ 157 good &= ~(mask&(padding_length ^ b)); 158 } 159 160 /* If any of the final |padding_length+1| bytes had the wrong value, 161 * one or more of the lower eight bits of |good| will be cleared. We 162 * AND the bottom 8 bits together and duplicate the result to all the 163 * bits. */ 164 good &= good >> 4; 165 good &= good >> 2; 166 good &= good >> 1; 167 good <<= sizeof(good)*8 - 1; 168 good = DUPLICATE_MSB_TO_ALL(good); 169 170 padding_length = good & (padding_length + 1); 171 rec->length -= padding_length; 172 rec->padding_length = padding_length; 173 174 return (int)((good & 1) | (~good & -1)); 175 } 176 177 /* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in 178 * constant time (independent of the concrete value of rec->length, which may 179 * vary within a 256-byte window). 180 * 181 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to 182 * this function. 183 * 184 * On entry: 185 * rec->orig_len >= md_size 186 * md_size <= EVP_MAX_MD_SIZE 187 * 188 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with 189 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into 190 * a single or pair of cache-lines, then the variable memory accesses don't 191 * actually affect the timing. CPUs with smaller cache-lines [if any] are 192 * not multi-core and are not considered vulnerable to cache-timing attacks. 193 */ 194 #define CBC_MAC_ROTATE_IN_PLACE 195 196 void 197 ssl3_cbc_copy_mac(unsigned char* out, const SSL3_RECORD_INTERNAL *rec, 198 unsigned int md_size, unsigned int orig_len) 199 { 200 #if defined(CBC_MAC_ROTATE_IN_PLACE) 201 unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; 202 unsigned char *rotated_mac; 203 #else 204 unsigned char rotated_mac[EVP_MAX_MD_SIZE]; 205 #endif 206 207 /* mac_end is the index of |rec->data| just after the end of the MAC. */ 208 unsigned int mac_end = rec->length; 209 unsigned int mac_start = mac_end - md_size; 210 /* scan_start contains the number of bytes that we can ignore because 211 * the MAC's position can only vary by 255 bytes. */ 212 unsigned int scan_start = 0; 213 unsigned int i, j; 214 unsigned int div_spoiler; 215 unsigned int rotate_offset; 216 217 OPENSSL_assert(orig_len >= md_size); 218 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 219 220 #if defined(CBC_MAC_ROTATE_IN_PLACE) 221 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf)&63); 222 #endif 223 224 /* This information is public so it's safe to branch based on it. */ 225 if (orig_len > md_size + 255 + 1) 226 scan_start = orig_len - (md_size + 255 + 1); 227 /* div_spoiler contains a multiple of md_size that is used to cause the 228 * modulo operation to be constant time. Without this, the time varies 229 * based on the amount of padding when running on Intel chips at least. 230 * 231 * The aim of right-shifting md_size is so that the compiler doesn't 232 * figure out that it can remove div_spoiler as that would require it 233 * to prove that md_size is always even, which I hope is beyond it. */ 234 div_spoiler = md_size >> 1; 235 div_spoiler <<= (sizeof(div_spoiler) - 1) * 8; 236 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; 237 238 memset(rotated_mac, 0, md_size); 239 for (i = scan_start, j = 0; i < orig_len; i++) { 240 unsigned char mac_started = constant_time_ge(i, mac_start); 241 unsigned char mac_ended = constant_time_ge(i, mac_end); 242 unsigned char b = rec->data[i]; 243 rotated_mac[j++] |= b & mac_started & ~mac_ended; 244 j &= constant_time_lt(j, md_size); 245 } 246 247 /* Now rotate the MAC */ 248 #if defined(CBC_MAC_ROTATE_IN_PLACE) 249 j = 0; 250 for (i = 0; i < md_size; i++) { 251 /* in case cache-line is 32 bytes, touch second line */ 252 ((volatile unsigned char *)rotated_mac)[rotate_offset^32]; 253 out[j++] = rotated_mac[rotate_offset++]; 254 rotate_offset &= constant_time_lt(rotate_offset, md_size); 255 } 256 #else 257 memset(out, 0, md_size); 258 rotate_offset = md_size - rotate_offset; 259 rotate_offset &= constant_time_lt(rotate_offset, md_size); 260 for (i = 0; i < md_size; i++) { 261 for (j = 0; j < md_size; j++) 262 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); 263 rotate_offset++; 264 rotate_offset &= constant_time_lt(rotate_offset, md_size); 265 } 266 #endif 267 } 268 269 #define l2n(l,c) (*((c)++)=(unsigned char)(((l)>>24)&0xff), \ 270 *((c)++)=(unsigned char)(((l)>>16)&0xff), \ 271 *((c)++)=(unsigned char)(((l)>> 8)&0xff), \ 272 *((c)++)=(unsigned char)(((l) )&0xff)) 273 274 #define l2n8(l,c) (*((c)++)=(unsigned char)(((l)>>56)&0xff), \ 275 *((c)++)=(unsigned char)(((l)>>48)&0xff), \ 276 *((c)++)=(unsigned char)(((l)>>40)&0xff), \ 277 *((c)++)=(unsigned char)(((l)>>32)&0xff), \ 278 *((c)++)=(unsigned char)(((l)>>24)&0xff), \ 279 *((c)++)=(unsigned char)(((l)>>16)&0xff), \ 280 *((c)++)=(unsigned char)(((l)>> 8)&0xff), \ 281 *((c)++)=(unsigned char)(((l) )&0xff)) 282 283 /* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 284 * little-endian order. The value of p is advanced by four. */ 285 #define u32toLE(n, p) \ 286 (*((p)++)=(unsigned char)(n), \ 287 *((p)++)=(unsigned char)(n>>8), \ 288 *((p)++)=(unsigned char)(n>>16), \ 289 *((p)++)=(unsigned char)(n>>24)) 290 291 /* These functions serialize the state of a hash and thus perform the standard 292 * "final" operation without adding the padding and length that such a function 293 * typically does. */ 294 static void 295 tls1_md5_final_raw(void* ctx, unsigned char *md_out) 296 { 297 MD5_CTX *md5 = ctx; 298 u32toLE(md5->A, md_out); 299 u32toLE(md5->B, md_out); 300 u32toLE(md5->C, md_out); 301 u32toLE(md5->D, md_out); 302 } 303 304 static void 305 tls1_sha1_final_raw(void* ctx, unsigned char *md_out) 306 { 307 SHA_CTX *sha1 = ctx; 308 l2n(sha1->h0, md_out); 309 l2n(sha1->h1, md_out); 310 l2n(sha1->h2, md_out); 311 l2n(sha1->h3, md_out); 312 l2n(sha1->h4, md_out); 313 } 314 315 static void 316 tls1_sha256_final_raw(void* ctx, unsigned char *md_out) 317 { 318 SHA256_CTX *sha256 = ctx; 319 unsigned int i; 320 321 for (i = 0; i < 8; i++) { 322 l2n(sha256->h[i], md_out); 323 } 324 } 325 326 static void 327 tls1_sha512_final_raw(void* ctx, unsigned char *md_out) 328 { 329 SHA512_CTX *sha512 = ctx; 330 unsigned int i; 331 332 for (i = 0; i < 8; i++) { 333 l2n8(sha512->h[i], md_out); 334 } 335 } 336 337 /* Largest hash context ever used by the functions above. */ 338 #define LARGEST_DIGEST_CTX SHA512_CTX 339 340 /* Type giving the alignment needed by the above */ 341 #define LARGEST_DIGEST_CTX_ALIGNMENT SHA_LONG64 342 343 /* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 344 * which ssl3_cbc_digest_record supports. */ 345 char 346 ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) 347 { 348 switch (EVP_MD_CTX_type(ctx)) { 349 case NID_md5: 350 case NID_sha1: 351 case NID_sha224: 352 case NID_sha256: 353 case NID_sha384: 354 case NID_sha512: 355 return 1; 356 default: 357 return 0; 358 } 359 } 360 361 /* ssl3_cbc_digest_record computes the MAC of a decrypted, padded TLS 362 * record. 363 * 364 * ctx: the EVP_MD_CTX from which we take the hash function. 365 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 366 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 367 * md_out_size: if non-NULL, the number of output bytes is written here. 368 * header: the 13-byte, TLS record header. 369 * data: the record data itself, less any preceeding explicit IV. 370 * data_plus_mac_size: the secret, reported length of the data and MAC 371 * once the padding has been removed. 372 * data_plus_mac_plus_padding_size: the public length of the whole 373 * record, including padding. 374 * 375 * On entry: by virtue of having been through one of the remove_padding 376 * functions, above, we know that data_plus_mac_size is large enough to contain 377 * a padding byte and MAC. (If the padding was invalid, it might contain the 378 * padding too. ) 379 */ 380 int 381 ssl3_cbc_digest_record(const EVP_MD_CTX *ctx, unsigned char* md_out, 382 size_t* md_out_size, const unsigned char header[13], 383 const unsigned char *data, size_t data_plus_mac_size, 384 size_t data_plus_mac_plus_padding_size, const unsigned char *mac_secret, 385 unsigned int mac_secret_length) 386 { 387 union { 388 /* 389 * Alignment here is to allow this to be cast as SHA512_CTX 390 * without losing alignment required by the 64-bit SHA_LONG64 391 * integer it contains. 392 */ 393 LARGEST_DIGEST_CTX_ALIGNMENT align; 394 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; 395 } md_state; 396 void (*md_final_raw)(void *ctx, unsigned char *md_out); 397 void (*md_transform)(void *ctx, const unsigned char *block); 398 unsigned int md_size, md_block_size = 64; 399 unsigned int header_length, variance_blocks, 400 len, max_mac_bytes, num_blocks, 401 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 402 unsigned int bits; /* at most 18 bits */ 403 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 404 /* hmac_pad is the masked HMAC key. */ 405 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 406 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 407 unsigned char mac_out[EVP_MAX_MD_SIZE]; 408 unsigned int i, j, md_out_size_u; 409 EVP_MD_CTX md_ctx; 410 /* mdLengthSize is the number of bytes in the length field that terminates 411 * the hash. */ 412 unsigned int md_length_size = 8; 413 char length_is_big_endian = 1; 414 415 /* This is a, hopefully redundant, check that allows us to forget about 416 * many possible overflows later in this function. */ 417 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024); 418 419 switch (EVP_MD_CTX_type(ctx)) { 420 case NID_md5: 421 MD5_Init((MD5_CTX*)md_state.c); 422 md_final_raw = tls1_md5_final_raw; 423 md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform; 424 md_size = 16; 425 length_is_big_endian = 0; 426 break; 427 case NID_sha1: 428 SHA1_Init((SHA_CTX*)md_state.c); 429 md_final_raw = tls1_sha1_final_raw; 430 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform; 431 md_size = 20; 432 break; 433 case NID_sha224: 434 SHA224_Init((SHA256_CTX*)md_state.c); 435 md_final_raw = tls1_sha256_final_raw; 436 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 437 md_size = 224/8; 438 break; 439 case NID_sha256: 440 SHA256_Init((SHA256_CTX*)md_state.c); 441 md_final_raw = tls1_sha256_final_raw; 442 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 443 md_size = 32; 444 break; 445 case NID_sha384: 446 SHA384_Init((SHA512_CTX*)md_state.c); 447 md_final_raw = tls1_sha512_final_raw; 448 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 449 md_size = 384/8; 450 md_block_size = 128; 451 md_length_size = 16; 452 break; 453 case NID_sha512: 454 SHA512_Init((SHA512_CTX*)md_state.c); 455 md_final_raw = tls1_sha512_final_raw; 456 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 457 md_size = 64; 458 md_block_size = 128; 459 md_length_size = 16; 460 break; 461 default: 462 /* ssl3_cbc_record_digest_supported should have been 463 * called first to check that the hash function is 464 * supported. */ 465 OPENSSL_assert(0); 466 if (md_out_size) 467 *md_out_size = 0; 468 return 0; 469 } 470 471 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 472 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 473 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 474 475 header_length = 13; 476 477 /* variance_blocks is the number of blocks of the hash that we have to 478 * calculate in constant time because they could be altered by the 479 * padding value. 480 * 481 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 482 * required to be minimal. Therefore we say that the final six blocks 483 * can vary based on the padding. 484 * 485 * Later in the function, if the message is short and there obviously 486 * cannot be this many blocks then variance_blocks can be reduced. */ 487 variance_blocks = 6; 488 /* From now on we're dealing with the MAC, which conceptually has 13 489 * bytes of `header' before the start of the data (TLS) */ 490 len = data_plus_mac_plus_padding_size + header_length; 491 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including 492 * |header|, assuming that there's no padding. */ 493 max_mac_bytes = len - md_size - 1; 494 /* num_blocks is the maximum number of hash blocks. */ 495 num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size; 496 /* In order to calculate the MAC in constant time we have to handle 497 * the final blocks specially because the padding value could cause the 498 * end to appear somewhere in the final |variance_blocks| blocks and we 499 * can't leak where. However, |num_starting_blocks| worth of data can 500 * be hashed right away because no padding value can affect whether 501 * they are plaintext. */ 502 num_starting_blocks = 0; 503 /* k is the starting byte offset into the conceptual header||data where 504 * we start processing. */ 505 k = 0; 506 /* mac_end_offset is the index just past the end of the data to be 507 * MACed. */ 508 mac_end_offset = data_plus_mac_size + header_length - md_size; 509 /* c is the index of the 0x80 byte in the final hash block that 510 * contains application data. */ 511 c = mac_end_offset % md_block_size; 512 /* index_a is the hash block number that contains the 0x80 terminating 513 * value. */ 514 index_a = mac_end_offset / md_block_size; 515 /* index_b is the hash block number that contains the 64-bit hash 516 * length, in bits. */ 517 index_b = (mac_end_offset + md_length_size) / md_block_size; 518 /* bits is the hash-length in bits. It includes the additional hash 519 * block for the masked HMAC key. */ 520 521 if (num_blocks > variance_blocks) { 522 num_starting_blocks = num_blocks - variance_blocks; 523 k = md_block_size*num_starting_blocks; 524 } 525 526 bits = 8*mac_end_offset; 527 /* Compute the initial HMAC block. */ 528 bits += 8*md_block_size; 529 memset(hmac_pad, 0, md_block_size); 530 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad)); 531 memcpy(hmac_pad, mac_secret, mac_secret_length); 532 for (i = 0; i < md_block_size; i++) 533 hmac_pad[i] ^= 0x36; 534 535 md_transform(md_state.c, hmac_pad); 536 537 if (length_is_big_endian) { 538 memset(length_bytes, 0, md_length_size - 4); 539 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); 540 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); 541 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); 542 length_bytes[md_length_size - 1] = (unsigned char)bits; 543 } else { 544 memset(length_bytes, 0, md_length_size); 545 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); 546 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); 547 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); 548 length_bytes[md_length_size - 8] = (unsigned char)bits; 549 } 550 551 if (k > 0) { 552 /* k is a multiple of md_block_size. */ 553 memcpy(first_block, header, 13); 554 memcpy(first_block + 13, data, md_block_size - 13); 555 md_transform(md_state.c, first_block); 556 for (i = 1; i < k/md_block_size; i++) 557 md_transform(md_state.c, data + md_block_size*i - 13); 558 } 559 560 memset(mac_out, 0, sizeof(mac_out)); 561 562 /* We now process the final hash blocks. For each block, we construct 563 * it in constant time. If the |i==index_a| then we'll include the 0x80 564 * bytes and zero pad etc. For each block we selectively copy it, in 565 * constant time, to |mac_out|. */ 566 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks; i++) { 567 unsigned char block[MAX_HASH_BLOCK_SIZE]; 568 unsigned char is_block_a = constant_time_eq_8(i, index_a); 569 unsigned char is_block_b = constant_time_eq_8(i, index_b); 570 for (j = 0; j < md_block_size; j++) { 571 unsigned char b = 0, is_past_c, is_past_cp1; 572 if (k < header_length) 573 b = header[k]; 574 else if (k < data_plus_mac_plus_padding_size + header_length) 575 b = data[k - header_length]; 576 k++; 577 578 is_past_c = is_block_a & constant_time_ge(j, c); 579 is_past_cp1 = is_block_a & constant_time_ge(j, c + 1); 580 /* If this is the block containing the end of the 581 * application data, and we are at the offset for the 582 * 0x80 value, then overwrite b with 0x80. */ 583 b = (b&~is_past_c) | (0x80&is_past_c); 584 /* If this is the block containing the end of the 585 * application data and we're past the 0x80 value then 586 * just write zero. */ 587 b = b&~is_past_cp1; 588 /* If this is index_b (the final block), but not 589 * index_a (the end of the data), then the 64-bit 590 * length didn't fit into index_a and we're having to 591 * add an extra block of zeros. */ 592 b &= ~is_block_b | is_block_a; 593 594 /* The final bytes of one of the blocks contains the 595 * length. */ 596 if (j >= md_block_size - md_length_size) { 597 /* If this is index_b, write a length byte. */ 598 b = (b&~is_block_b) | (is_block_b&length_bytes[j - (md_block_size - md_length_size)]); 599 } 600 block[j] = b; 601 } 602 603 md_transform(md_state.c, block); 604 md_final_raw(md_state.c, block); 605 /* If this is index_b, copy the hash value to |mac_out|. */ 606 for (j = 0; j < md_size; j++) 607 mac_out[j] |= block[j]&is_block_b; 608 } 609 610 EVP_MD_CTX_init(&md_ctx); 611 if (!EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */)) { 612 EVP_MD_CTX_cleanup(&md_ctx); 613 return 0; 614 } 615 616 /* Complete the HMAC in the standard manner. */ 617 for (i = 0; i < md_block_size; i++) 618 hmac_pad[i] ^= 0x6a; 619 620 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 621 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 622 623 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 624 if (md_out_size) 625 *md_out_size = md_out_size_u; 626 EVP_MD_CTX_cleanup(&md_ctx); 627 628 return 1; 629 } 630