s3_cbc.c revision 1.13
1/* $OpenBSD: s3_cbc.c,v 1.13 2016/11/06 17:21:04 jsing 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)(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. */ 80static unsigned 81constant_time_lt(unsigned a, unsigned 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. */ 88static unsigned 89constant_time_ge(unsigned a, unsigned 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. */ 96static unsigned char 97constant_time_eq_8(unsigned a, unsigned b) 98{ 99 unsigned 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. */ 115int 116tls1_cbc_remove_padding(const SSL* s, SSL3_RECORD *rec, unsigned block_size, 117 unsigned mac_size) 118{ 119 unsigned padding_length, good, to_check, i; 120 const unsigned 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 if (EVP_CIPHER_flags(s->enc_read_ctx->cipher) & EVP_CIPH_FLAG_AEAD_CIPHER) { 139 /* padding is already verified */ 140 rec->length -= padding_length + 1; 141 return 1; 142 } 143 144 good = constant_time_ge(rec->length, overhead + padding_length); 145 /* The padding consists of a length byte at the end of the record and 146 * then that many bytes of padding, all with the same value as the 147 * length byte. Thus, with the length byte included, there are i+1 148 * bytes of padding. 149 * 150 * We can't check just |padding_length+1| bytes because that leaks 151 * decrypted information. Therefore we always have to check the maximum 152 * amount of padding possible. (Again, the length of the record is 153 * public information so we can use it.) */ 154 to_check = 255; /* maximum amount of padding. */ 155 if (to_check > rec->length - 1) 156 to_check = rec->length - 1; 157 158 for (i = 0; i < to_check; i++) { 159 unsigned char mask = constant_time_ge(padding_length, i); 160 unsigned char b = rec->data[rec->length - 1 - i]; 161 /* The final |padding_length+1| bytes should all have the value 162 * |padding_length|. Therefore the XOR should be zero. */ 163 good &= ~(mask&(padding_length ^ b)); 164 } 165 166 /* If any of the final |padding_length+1| bytes had the wrong value, 167 * one or more of the lower eight bits of |good| will be cleared. We 168 * AND the bottom 8 bits together and duplicate the result to all the 169 * bits. */ 170 good &= good >> 4; 171 good &= good >> 2; 172 good &= good >> 1; 173 good <<= sizeof(good)*8 - 1; 174 good = DUPLICATE_MSB_TO_ALL(good); 175 176 padding_length = good & (padding_length + 1); 177 rec->length -= padding_length; 178 rec->type |= padding_length<<8; /* kludge: pass padding length */ 179 180 return (int)((good & 1) | (~good & -1)); 181} 182 183/* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in 184 * constant time (independent of the concrete value of rec->length, which may 185 * vary within a 256-byte window). 186 * 187 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to 188 * this function. 189 * 190 * On entry: 191 * rec->orig_len >= md_size 192 * md_size <= EVP_MAX_MD_SIZE 193 * 194 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with 195 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into 196 * a single or pair of cache-lines, then the variable memory accesses don't 197 * actually affect the timing. CPUs with smaller cache-lines [if any] are 198 * not multi-core and are not considered vulnerable to cache-timing attacks. 199 */ 200#define CBC_MAC_ROTATE_IN_PLACE 201 202void 203ssl3_cbc_copy_mac(unsigned char* out, const SSL3_RECORD *rec, 204 unsigned md_size, unsigned orig_len) 205{ 206#if defined(CBC_MAC_ROTATE_IN_PLACE) 207 unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; 208 unsigned char *rotated_mac; 209#else 210 unsigned char rotated_mac[EVP_MAX_MD_SIZE]; 211#endif 212 213 /* mac_end is the index of |rec->data| just after the end of the MAC. */ 214 unsigned mac_end = rec->length; 215 unsigned mac_start = mac_end - md_size; 216 /* scan_start contains the number of bytes that we can ignore because 217 * the MAC's position can only vary by 255 bytes. */ 218 unsigned scan_start = 0; 219 unsigned i, j; 220 unsigned div_spoiler; 221 unsigned rotate_offset; 222 223 OPENSSL_assert(orig_len >= md_size); 224 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 225 226#if defined(CBC_MAC_ROTATE_IN_PLACE) 227 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf)&63); 228#endif 229 230 /* This information is public so it's safe to branch based on it. */ 231 if (orig_len > md_size + 255 + 1) 232 scan_start = orig_len - (md_size + 255 + 1); 233 /* div_spoiler contains a multiple of md_size that is used to cause the 234 * modulo operation to be constant time. Without this, the time varies 235 * based on the amount of padding when running on Intel chips at least. 236 * 237 * The aim of right-shifting md_size is so that the compiler doesn't 238 * figure out that it can remove div_spoiler as that would require it 239 * to prove that md_size is always even, which I hope is beyond it. */ 240 div_spoiler = md_size >> 1; 241 div_spoiler <<= (sizeof(div_spoiler) - 1) * 8; 242 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; 243 244 memset(rotated_mac, 0, md_size); 245 for (i = scan_start, j = 0; i < orig_len; i++) { 246 unsigned char mac_started = constant_time_ge(i, mac_start); 247 unsigned char mac_ended = constant_time_ge(i, mac_end); 248 unsigned char b = rec->data[i]; 249 rotated_mac[j++] |= b & mac_started & ~mac_ended; 250 j &= constant_time_lt(j, md_size); 251 } 252 253 /* Now rotate the MAC */ 254#if defined(CBC_MAC_ROTATE_IN_PLACE) 255 j = 0; 256 for (i = 0; i < md_size; i++) { 257 /* in case cache-line is 32 bytes, touch second line */ 258 ((volatile unsigned char *)rotated_mac)[rotate_offset^32]; 259 out[j++] = rotated_mac[rotate_offset++]; 260 rotate_offset &= constant_time_lt(rotate_offset, md_size); 261 } 262#else 263 memset(out, 0, md_size); 264 rotate_offset = md_size - rotate_offset; 265 rotate_offset &= constant_time_lt(rotate_offset, md_size); 266 for (i = 0; i < md_size; i++) { 267 for (j = 0; j < md_size; j++) 268 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); 269 rotate_offset++; 270 rotate_offset &= constant_time_lt(rotate_offset, md_size); 271 } 272#endif 273} 274 275/* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 276 * little-endian order. The value of p is advanced by four. */ 277#define u32toLE(n, p) \ 278 (*((p)++)=(unsigned char)(n), \ 279 *((p)++)=(unsigned char)(n>>8), \ 280 *((p)++)=(unsigned char)(n>>16), \ 281 *((p)++)=(unsigned char)(n>>24)) 282 283/* These functions serialize the state of a hash and thus perform the standard 284 * "final" operation without adding the padding and length that such a function 285 * typically does. */ 286static void 287tls1_md5_final_raw(void* ctx, unsigned char *md_out) 288{ 289 MD5_CTX *md5 = ctx; 290 u32toLE(md5->A, md_out); 291 u32toLE(md5->B, md_out); 292 u32toLE(md5->C, md_out); 293 u32toLE(md5->D, md_out); 294} 295 296static void 297tls1_sha1_final_raw(void* ctx, unsigned char *md_out) 298{ 299 SHA_CTX *sha1 = ctx; 300 l2n(sha1->h0, md_out); 301 l2n(sha1->h1, md_out); 302 l2n(sha1->h2, md_out); 303 l2n(sha1->h3, md_out); 304 l2n(sha1->h4, md_out); 305} 306#define LARGEST_DIGEST_CTX SHA_CTX 307 308static void 309tls1_sha256_final_raw(void* ctx, unsigned char *md_out) 310{ 311 SHA256_CTX *sha256 = ctx; 312 unsigned i; 313 314 for (i = 0; i < 8; i++) { 315 l2n(sha256->h[i], md_out); 316 } 317} 318#undef LARGEST_DIGEST_CTX 319#define LARGEST_DIGEST_CTX SHA256_CTX 320 321static void 322tls1_sha512_final_raw(void* ctx, unsigned char *md_out) 323{ 324 SHA512_CTX *sha512 = ctx; 325 unsigned i; 326 327 for (i = 0; i < 8; i++) { 328 l2n8(sha512->h[i], md_out); 329 } 330} 331#undef LARGEST_DIGEST_CTX 332#define LARGEST_DIGEST_CTX SHA512_CTX 333 334/* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 335 * which ssl3_cbc_digest_record supports. */ 336char 337ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) 338{ 339 switch (EVP_MD_CTX_type(ctx)) { 340 case NID_md5: 341 case NID_sha1: 342 case NID_sha224: 343 case NID_sha256: 344 case NID_sha384: 345 case NID_sha512: 346 return 1; 347 default: 348 return 0; 349 } 350} 351 352/* ssl3_cbc_digest_record computes the MAC of a decrypted, padded TLS 353 * record. 354 * 355 * ctx: the EVP_MD_CTX from which we take the hash function. 356 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 357 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 358 * md_out_size: if non-NULL, the number of output bytes is written here. 359 * header: the 13-byte, TLS record header. 360 * data: the record data itself, less any preceeding explicit IV. 361 * data_plus_mac_size: the secret, reported length of the data and MAC 362 * once the padding has been removed. 363 * data_plus_mac_plus_padding_size: the public length of the whole 364 * record, including padding. 365 * 366 * On entry: by virtue of having been through one of the remove_padding 367 * functions, above, we know that data_plus_mac_size is large enough to contain 368 * a padding byte and MAC. (If the padding was invalid, it might contain the 369 * padding too. ) */ 370int 371ssl3_cbc_digest_record(const EVP_MD_CTX *ctx, unsigned char* md_out, 372 size_t* md_out_size, const unsigned char header[13], 373 const unsigned char *data, size_t data_plus_mac_size, 374 size_t data_plus_mac_plus_padding_size, const unsigned char *mac_secret, 375 unsigned mac_secret_length) 376{ 377 union { double align; 378 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; 379 } md_state; 380 void (*md_final_raw)(void *ctx, unsigned char *md_out); 381 void (*md_transform)(void *ctx, const unsigned char *block); 382 unsigned md_size, md_block_size = 64; 383 unsigned header_length, variance_blocks, 384 len, max_mac_bytes, num_blocks, 385 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 386 unsigned int bits; /* at most 18 bits */ 387 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 388 /* hmac_pad is the masked HMAC key. */ 389 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 390 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 391 unsigned char mac_out[EVP_MAX_MD_SIZE]; 392 unsigned i, j, md_out_size_u; 393 EVP_MD_CTX md_ctx; 394 /* mdLengthSize is the number of bytes in the length field that terminates 395 * the hash. */ 396 unsigned md_length_size = 8; 397 char length_is_big_endian = 1; 398 399 /* This is a, hopefully redundant, check that allows us to forget about 400 * many possible overflows later in this function. */ 401 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024); 402 403 switch (EVP_MD_CTX_type(ctx)) { 404 case NID_md5: 405 MD5_Init((MD5_CTX*)md_state.c); 406 md_final_raw = tls1_md5_final_raw; 407 md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform; 408 md_size = 16; 409 length_is_big_endian = 0; 410 break; 411 case NID_sha1: 412 SHA1_Init((SHA_CTX*)md_state.c); 413 md_final_raw = tls1_sha1_final_raw; 414 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform; 415 md_size = 20; 416 break; 417 case NID_sha224: 418 SHA224_Init((SHA256_CTX*)md_state.c); 419 md_final_raw = tls1_sha256_final_raw; 420 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 421 md_size = 224/8; 422 break; 423 case NID_sha256: 424 SHA256_Init((SHA256_CTX*)md_state.c); 425 md_final_raw = tls1_sha256_final_raw; 426 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 427 md_size = 32; 428 break; 429 case NID_sha384: 430 SHA384_Init((SHA512_CTX*)md_state.c); 431 md_final_raw = tls1_sha512_final_raw; 432 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 433 md_size = 384/8; 434 md_block_size = 128; 435 md_length_size = 16; 436 break; 437 case NID_sha512: 438 SHA512_Init((SHA512_CTX*)md_state.c); 439 md_final_raw = tls1_sha512_final_raw; 440 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 441 md_size = 64; 442 md_block_size = 128; 443 md_length_size = 16; 444 break; 445 default: 446 /* ssl3_cbc_record_digest_supported should have been 447 * called first to check that the hash function is 448 * supported. */ 449 OPENSSL_assert(0); 450 if (md_out_size) 451 *md_out_size = 0; 452 return 0; 453 } 454 455 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 456 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 457 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 458 459 header_length = 13; 460 461 /* variance_blocks is the number of blocks of the hash that we have to 462 * calculate in constant time because they could be altered by the 463 * padding value. 464 * 465 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 466 * required to be minimal. Therefore we say that the final six blocks 467 * can vary based on the padding. 468 * 469 * Later in the function, if the message is short and there obviously 470 * cannot be this many blocks then variance_blocks can be reduced. */ 471 variance_blocks = 6; 472 /* From now on we're dealing with the MAC, which conceptually has 13 473 * bytes of `header' before the start of the data (TLS) */ 474 len = data_plus_mac_plus_padding_size + header_length; 475 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including 476 * |header|, assuming that there's no padding. */ 477 max_mac_bytes = len - md_size - 1; 478 /* num_blocks is the maximum number of hash blocks. */ 479 num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size; 480 /* In order to calculate the MAC in constant time we have to handle 481 * the final blocks specially because the padding value could cause the 482 * end to appear somewhere in the final |variance_blocks| blocks and we 483 * can't leak where. However, |num_starting_blocks| worth of data can 484 * be hashed right away because no padding value can affect whether 485 * they are plaintext. */ 486 num_starting_blocks = 0; 487 /* k is the starting byte offset into the conceptual header||data where 488 * we start processing. */ 489 k = 0; 490 /* mac_end_offset is the index just past the end of the data to be 491 * MACed. */ 492 mac_end_offset = data_plus_mac_size + header_length - md_size; 493 /* c is the index of the 0x80 byte in the final hash block that 494 * contains application data. */ 495 c = mac_end_offset % md_block_size; 496 /* index_a is the hash block number that contains the 0x80 terminating 497 * value. */ 498 index_a = mac_end_offset / md_block_size; 499 /* index_b is the hash block number that contains the 64-bit hash 500 * length, in bits. */ 501 index_b = (mac_end_offset + md_length_size) / md_block_size; 502 /* bits is the hash-length in bits. It includes the additional hash 503 * block for the masked HMAC key. */ 504 505 if (num_blocks > variance_blocks) { 506 num_starting_blocks = num_blocks - variance_blocks; 507 k = md_block_size*num_starting_blocks; 508 } 509 510 bits = 8*mac_end_offset; 511 /* Compute the initial HMAC block. */ 512 bits += 8*md_block_size; 513 memset(hmac_pad, 0, md_block_size); 514 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad)); 515 memcpy(hmac_pad, mac_secret, mac_secret_length); 516 for (i = 0; i < md_block_size; i++) 517 hmac_pad[i] ^= 0x36; 518 519 md_transform(md_state.c, hmac_pad); 520 521 if (length_is_big_endian) { 522 memset(length_bytes, 0, md_length_size - 4); 523 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); 524 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); 525 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); 526 length_bytes[md_length_size - 1] = (unsigned char)bits; 527 } else { 528 memset(length_bytes, 0, md_length_size); 529 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); 530 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); 531 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); 532 length_bytes[md_length_size - 8] = (unsigned char)bits; 533 } 534 535 if (k > 0) { 536 /* k is a multiple of md_block_size. */ 537 memcpy(first_block, header, 13); 538 memcpy(first_block + 13, data, md_block_size - 13); 539 md_transform(md_state.c, first_block); 540 for (i = 1; i < k/md_block_size; i++) 541 md_transform(md_state.c, data + md_block_size*i - 13); 542 } 543 544 memset(mac_out, 0, sizeof(mac_out)); 545 546 /* We now process the final hash blocks. For each block, we construct 547 * it in constant time. If the |i==index_a| then we'll include the 0x80 548 * bytes and zero pad etc. For each block we selectively copy it, in 549 * constant time, to |mac_out|. */ 550 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks; i++) { 551 unsigned char block[MAX_HASH_BLOCK_SIZE]; 552 unsigned char is_block_a = constant_time_eq_8(i, index_a); 553 unsigned char is_block_b = constant_time_eq_8(i, index_b); 554 for (j = 0; j < md_block_size; j++) { 555 unsigned char b = 0, is_past_c, is_past_cp1; 556 if (k < header_length) 557 b = header[k]; 558 else if (k < data_plus_mac_plus_padding_size + header_length) 559 b = data[k - header_length]; 560 k++; 561 562 is_past_c = is_block_a & constant_time_ge(j, c); 563 is_past_cp1 = is_block_a & constant_time_ge(j, c + 1); 564 /* If this is the block containing the end of the 565 * application data, and we are at the offset for the 566 * 0x80 value, then overwrite b with 0x80. */ 567 b = (b&~is_past_c) | (0x80&is_past_c); 568 /* If this is the block containing the end of the 569 * application data and we're past the 0x80 value then 570 * just write zero. */ 571 b = b&~is_past_cp1; 572 /* If this is index_b (the final block), but not 573 * index_a (the end of the data), then the 64-bit 574 * length didn't fit into index_a and we're having to 575 * add an extra block of zeros. */ 576 b &= ~is_block_b | is_block_a; 577 578 /* The final bytes of one of the blocks contains the 579 * length. */ 580 if (j >= md_block_size - md_length_size) { 581 /* If this is index_b, write a length byte. */ 582 b = (b&~is_block_b) | (is_block_b&length_bytes[j - (md_block_size - md_length_size)]); 583 } 584 block[j] = b; 585 } 586 587 md_transform(md_state.c, block); 588 md_final_raw(md_state.c, block); 589 /* If this is index_b, copy the hash value to |mac_out|. */ 590 for (j = 0; j < md_size; j++) 591 mac_out[j] |= block[j]&is_block_b; 592 } 593 594 EVP_MD_CTX_init(&md_ctx); 595 if (!EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */)) { 596 EVP_MD_CTX_cleanup(&md_ctx); 597 return 0; 598 } 599 600 /* Complete the HMAC in the standard manner. */ 601 for (i = 0; i < md_block_size; i++) 602 hmac_pad[i] ^= 0x6a; 603 604 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 605 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 606 607 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 608 if (md_out_size) 609 *md_out_size = md_out_size_u; 610 EVP_MD_CTX_cleanup(&md_ctx); 611 612 return 1; 613} 614