1/* ssl/s3_cbc.c */ 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 "../crypto/constant_time_locl.h" 57#include "ssl_locl.h" 58 59#include <openssl/md5.h> 60#include <openssl/sha.h> 61 62/* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length 63 * field. (SHA-384/512 have 128-bit length.) */ 64#define MAX_HASH_BIT_COUNT_BYTES 16 65 66/* MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support. 67 * Currently SHA-384/512 has a 128-byte block size and that's the largest 68 * supported by TLS.) */ 69#define MAX_HASH_BLOCK_SIZE 128 70 71/* ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC 72 * record in |rec| by updating |rec->length| in constant time. 73 * 74 * block_size: the block size of the cipher used to encrypt the record. 75 * returns: 76 * 0: (in non-constant time) if the record is publicly invalid. 77 * 1: if the padding was valid 78 * -1: otherwise. */ 79int ssl3_cbc_remove_padding(const SSL* s, 80 SSL3_RECORD *rec, 81 unsigned block_size, 82 unsigned mac_size) 83 { 84 unsigned padding_length, good; 85 const unsigned overhead = 1 /* padding length byte */ + mac_size; 86 87 /* These lengths are all public so we can test them in non-constant 88 * time. */ 89 if (overhead > rec->length) 90 return 0; 91 92 padding_length = rec->data[rec->length-1]; 93 good = constant_time_ge(rec->length, padding_length+overhead); 94 /* SSLv3 requires that the padding is minimal. */ 95 good &= constant_time_ge(block_size, padding_length+1); 96 padding_length = good & (padding_length+1); 97 rec->length -= padding_length; 98 rec->type |= padding_length<<8; /* kludge: pass padding length */ 99 return constant_time_select_int(good, 1, -1); 100 } 101 102/* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC 103 * record in |rec| in constant time and returns 1 if the padding is valid and 104 * -1 otherwise. It also removes any explicit IV from the start of the record 105 * without leaking any timing about whether there was enough space after the 106 * padding was removed. 107 * 108 * block_size: the block size of the cipher used to encrypt the record. 109 * returns: 110 * 0: (in non-constant time) if the record is publicly invalid. 111 * 1: if the padding was valid 112 * -1: otherwise. */ 113int tls1_cbc_remove_padding(const SSL* s, 114 SSL3_RECORD *rec, 115 unsigned block_size, 116 unsigned mac_size) 117 { 118 unsigned padding_length, good, to_check, i; 119 const unsigned overhead = 1 /* padding length byte */ + mac_size; 120 /* Check if version requires explicit IV */ 121 if (s->version == DTLS1_VERSION || s->version == DTLS1_BAD_VER) 122 { 123 /* These lengths are all public so we can test them in 124 * non-constant time. 125 */ 126 if (overhead + block_size > rec->length) 127 return 0; 128 /* We can now safely skip explicit IV */ 129 rec->data += block_size; 130 rec->input += block_size; 131 rec->length -= block_size; 132 } 133 else if (overhead > rec->length) 134 return 0; 135 136 padding_length = rec->data[rec->length-1]; 137 138 /* NB: if compression is in operation the first packet may not be of 139 * even length so the padding bug check cannot be performed. This bug 140 * workaround has been around since SSLeay so hopefully it is either 141 * fixed now or no buggy implementation supports compression [steve] 142 */ 143 if ( (s->options&SSL_OP_TLS_BLOCK_PADDING_BUG) && !s->expand) 144 { 145 /* First packet is even in size, so check */ 146 if ((memcmp(s->s3->read_sequence, "\0\0\0\0\0\0\0\0",8) == 0) && 147 !(padding_length & 1)) 148 { 149 s->s3->flags|=TLS1_FLAGS_TLS_PADDING_BUG; 150 } 151 if ((s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) && 152 padding_length > 0) 153 { 154 padding_length--; 155 } 156 } 157 158 good = constant_time_ge(rec->length, overhead+padding_length); 159 /* The padding consists of a length byte at the end of the record and 160 * then that many bytes of padding, all with the same value as the 161 * length byte. Thus, with the length byte included, there are i+1 162 * bytes of padding. 163 * 164 * We can't check just |padding_length+1| bytes because that leaks 165 * decrypted information. Therefore we always have to check the maximum 166 * amount of padding possible. (Again, the length of the record is 167 * public information so we can use it.) */ 168 to_check = 255; /* maximum amount of padding. */ 169 if (to_check > rec->length-1) 170 to_check = rec->length-1; 171 172 for (i = 0; i < to_check; i++) 173 { 174 unsigned char mask = constant_time_ge_8(padding_length, i); 175 unsigned char b = rec->data[rec->length-1-i]; 176 /* The final |padding_length+1| bytes should all have the value 177 * |padding_length|. Therefore the XOR should be zero. */ 178 good &= ~(mask&(padding_length ^ b)); 179 } 180 181 /* If any of the final |padding_length+1| bytes had the wrong value, 182 * one or more of the lower eight bits of |good| will be cleared. 183 */ 184 good = constant_time_eq(0xff, good & 0xff); 185 padding_length = good & (padding_length+1); 186 rec->length -= padding_length; 187 rec->type |= padding_length<<8; /* kludge: pass padding length */ 188 189 return constant_time_select_int(good, 1, -1); 190 } 191 192/* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in 193 * constant time (independent of the concrete value of rec->length, which may 194 * vary within a 256-byte window). 195 * 196 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to 197 * this function. 198 * 199 * On entry: 200 * rec->orig_len >= md_size 201 * md_size <= EVP_MAX_MD_SIZE 202 * 203 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with 204 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into 205 * a single or pair of cache-lines, then the variable memory accesses don't 206 * actually affect the timing. CPUs with smaller cache-lines [if any] are 207 * not multi-core and are not considered vulnerable to cache-timing attacks. 208 */ 209#define CBC_MAC_ROTATE_IN_PLACE 210 211void ssl3_cbc_copy_mac(unsigned char* out, 212 const SSL3_RECORD *rec, 213 unsigned md_size,unsigned orig_len) 214 { 215#if defined(CBC_MAC_ROTATE_IN_PLACE) 216 unsigned char rotated_mac_buf[64+EVP_MAX_MD_SIZE]; 217 unsigned char *rotated_mac; 218#else 219 unsigned char rotated_mac[EVP_MAX_MD_SIZE]; 220#endif 221 222 /* mac_end is the index of |rec->data| just after the end of the MAC. */ 223 unsigned mac_end = rec->length; 224 unsigned mac_start = mac_end - md_size; 225 /* scan_start contains the number of bytes that we can ignore because 226 * the MAC's position can only vary by 255 bytes. */ 227 unsigned scan_start = 0; 228 unsigned i, j; 229 unsigned div_spoiler; 230 unsigned rotate_offset; 231 232 OPENSSL_assert(orig_len >= md_size); 233 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 234 235#if defined(CBC_MAC_ROTATE_IN_PLACE) 236 rotated_mac = rotated_mac_buf + ((0-(size_t)rotated_mac_buf)&63); 237#endif 238 239 /* This information is public so it's safe to branch based on it. */ 240 if (orig_len > md_size + 255 + 1) 241 scan_start = orig_len - (md_size + 255 + 1); 242 /* div_spoiler contains a multiple of md_size that is used to cause the 243 * modulo operation to be constant time. Without this, the time varies 244 * based on the amount of padding when running on Intel chips at least. 245 * 246 * The aim of right-shifting md_size is so that the compiler doesn't 247 * figure out that it can remove div_spoiler as that would require it 248 * to prove that md_size is always even, which I hope is beyond it. */ 249 div_spoiler = md_size >> 1; 250 div_spoiler <<= (sizeof(div_spoiler)-1)*8; 251 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; 252 253 memset(rotated_mac, 0, md_size); 254 for (i = scan_start, j = 0; i < orig_len; i++) 255 { 256 unsigned char mac_started = constant_time_ge_8(i, mac_start); 257 unsigned char mac_ended = constant_time_ge_8(i, mac_end); 258 unsigned char b = rec->data[i]; 259 rotated_mac[j++] |= b & mac_started & ~mac_ended; 260 j &= constant_time_lt(j,md_size); 261 } 262 263 /* Now rotate the MAC */ 264#if defined(CBC_MAC_ROTATE_IN_PLACE) 265 j = 0; 266 for (i = 0; i < md_size; i++) 267 { 268 /* in case cache-line is 32 bytes, touch second line */ 269 ((volatile unsigned char *)rotated_mac)[rotate_offset^32]; 270 out[j++] = rotated_mac[rotate_offset++]; 271 rotate_offset &= constant_time_lt(rotate_offset,md_size); 272 } 273#else 274 memset(out, 0, md_size); 275 rotate_offset = md_size - rotate_offset; 276 rotate_offset &= constant_time_lt(rotate_offset,md_size); 277 for (i = 0; i < md_size; i++) 278 { 279 for (j = 0; j < md_size; j++) 280 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); 281 rotate_offset++; 282 rotate_offset &= constant_time_lt(rotate_offset,md_size); 283 } 284#endif 285 } 286 287/* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 288 * little-endian order. The value of p is advanced by four. */ 289#define u32toLE(n, p) \ 290 (*((p)++)=(unsigned char)(n), \ 291 *((p)++)=(unsigned char)(n>>8), \ 292 *((p)++)=(unsigned char)(n>>16), \ 293 *((p)++)=(unsigned char)(n>>24)) 294 295/* These functions serialize the state of a hash and thus perform the standard 296 * "final" operation without adding the padding and length that such a function 297 * typically does. */ 298static void tls1_md5_final_raw(void* ctx, unsigned char *md_out) 299 { 300 MD5_CTX *md5 = ctx; 301 u32toLE(md5->A, md_out); 302 u32toLE(md5->B, md_out); 303 u32toLE(md5->C, md_out); 304 u32toLE(md5->D, md_out); 305 } 306 307static void tls1_sha1_final_raw(void* ctx, unsigned char *md_out) 308 { 309 SHA_CTX *sha1 = ctx; 310 l2n(sha1->h0, md_out); 311 l2n(sha1->h1, md_out); 312 l2n(sha1->h2, md_out); 313 l2n(sha1->h3, md_out); 314 l2n(sha1->h4, md_out); 315 } 316#define LARGEST_DIGEST_CTX SHA_CTX 317 318#ifndef OPENSSL_NO_SHA256 319static void tls1_sha256_final_raw(void* ctx, unsigned char *md_out) 320 { 321 SHA256_CTX *sha256 = ctx; 322 unsigned i; 323 324 for (i = 0; i < 8; i++) 325 { 326 l2n(sha256->h[i], md_out); 327 } 328 } 329#undef LARGEST_DIGEST_CTX 330#define LARGEST_DIGEST_CTX SHA256_CTX 331#endif 332 333#ifndef OPENSSL_NO_SHA512 334static void tls1_sha512_final_raw(void* ctx, unsigned char *md_out) 335 { 336 SHA512_CTX *sha512 = ctx; 337 unsigned i; 338 339 for (i = 0; i < 8; i++) 340 { 341 l2n8(sha512->h[i], md_out); 342 } 343 } 344#undef LARGEST_DIGEST_CTX 345#define LARGEST_DIGEST_CTX SHA512_CTX 346#endif 347 348/* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 349 * which ssl3_cbc_digest_record supports. */ 350char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) 351 { 352 switch (ctx->digest->type) 353 { 354 case NID_md5: 355 case NID_sha1: 356#ifndef OPENSSL_NO_SHA256 357 case NID_sha224: 358 case NID_sha256: 359#endif 360#ifndef OPENSSL_NO_SHA512 361 case NID_sha384: 362 case NID_sha512: 363#endif 364 return 1; 365 default: 366 return 0; 367 } 368 } 369 370/* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS 371 * record. 372 * 373 * ctx: the EVP_MD_CTX from which we take the hash function. 374 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 375 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 376 * md_out_size: if non-NULL, the number of output bytes is written here. 377 * header: the 13-byte, TLS record header. 378 * data: the record data itself, less any preceeding explicit IV. 379 * data_plus_mac_size: the secret, reported length of the data and MAC 380 * once the padding has been removed. 381 * data_plus_mac_plus_padding_size: the public length of the whole 382 * record, including padding. 383 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS. 384 * 385 * On entry: by virtue of having been through one of the remove_padding 386 * functions, above, we know that data_plus_mac_size is large enough to contain 387 * a padding byte and MAC. (If the padding was invalid, it might contain the 388 * padding too. ) */ 389void ssl3_cbc_digest_record( 390 const EVP_MD_CTX *ctx, 391 unsigned char* md_out, 392 size_t* md_out_size, 393 const unsigned char header[13], 394 const unsigned char *data, 395 size_t data_plus_mac_size, 396 size_t data_plus_mac_plus_padding_size, 397 const unsigned char *mac_secret, 398 unsigned mac_secret_length, 399 char is_sslv3) 400 { 401 union { double align; 402 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; } md_state; 403 void (*md_final_raw)(void *ctx, unsigned char *md_out); 404 void (*md_transform)(void *ctx, const unsigned char *block); 405 unsigned md_size, md_block_size = 64; 406 unsigned sslv3_pad_length = 40, header_length, variance_blocks, 407 len, max_mac_bytes, num_blocks, 408 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 409 unsigned int bits; /* at most 18 bits */ 410 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 411 /* hmac_pad is the masked HMAC key. */ 412 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 413 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 414 unsigned char mac_out[EVP_MAX_MD_SIZE]; 415 unsigned i, j, md_out_size_u; 416 EVP_MD_CTX md_ctx; 417 /* mdLengthSize is the number of bytes in the length field that terminates 418 * the hash. */ 419 unsigned md_length_size = 8; 420 char length_is_big_endian = 1; 421 422 /* This is a, hopefully redundant, check that allows us to forget about 423 * many possible overflows later in this function. */ 424 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024); 425 426 switch (ctx->digest->type) 427 { 428 case NID_md5: 429 MD5_Init((MD5_CTX*)md_state.c); 430 md_final_raw = tls1_md5_final_raw; 431 md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform; 432 md_size = 16; 433 sslv3_pad_length = 48; 434 length_is_big_endian = 0; 435 break; 436 case NID_sha1: 437 SHA1_Init((SHA_CTX*)md_state.c); 438 md_final_raw = tls1_sha1_final_raw; 439 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform; 440 md_size = 20; 441 break; 442#ifndef OPENSSL_NO_SHA256 443 case NID_sha224: 444 SHA224_Init((SHA256_CTX*)md_state.c); 445 md_final_raw = tls1_sha256_final_raw; 446 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 447 md_size = 224/8; 448 break; 449 case NID_sha256: 450 SHA256_Init((SHA256_CTX*)md_state.c); 451 md_final_raw = tls1_sha256_final_raw; 452 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform; 453 md_size = 32; 454 break; 455#endif 456#ifndef OPENSSL_NO_SHA512 457 case NID_sha384: 458 SHA384_Init((SHA512_CTX*)md_state.c); 459 md_final_raw = tls1_sha512_final_raw; 460 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 461 md_size = 384/8; 462 md_block_size = 128; 463 md_length_size = 16; 464 break; 465 case NID_sha512: 466 SHA512_Init((SHA512_CTX*)md_state.c); 467 md_final_raw = tls1_sha512_final_raw; 468 md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform; 469 md_size = 64; 470 md_block_size = 128; 471 md_length_size = 16; 472 break; 473#endif 474 default: 475 /* ssl3_cbc_record_digest_supported should have been 476 * called first to check that the hash function is 477 * supported. */ 478 OPENSSL_assert(0); 479 if (md_out_size) 480 *md_out_size = -1; 481 return; 482 } 483 484 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 485 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 486 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 487 488 header_length = 13; 489 if (is_sslv3) 490 { 491 header_length = 492 mac_secret_length + 493 sslv3_pad_length + 494 8 /* sequence number */ + 495 1 /* record type */ + 496 2 /* record length */; 497 } 498 499 /* variance_blocks is the number of blocks of the hash that we have to 500 * calculate in constant time because they could be altered by the 501 * padding value. 502 * 503 * In SSLv3, the padding must be minimal so the end of the plaintext 504 * varies by, at most, 15+20 = 35 bytes. (We conservatively assume that 505 * the MAC size varies from 0..20 bytes.) In case the 9 bytes of hash 506 * termination (0x80 + 64-bit length) don't fit in the final block, we 507 * say that the final two blocks can vary based on the padding. 508 * 509 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 510 * required to be minimal. Therefore we say that the final six blocks 511 * can vary based on the padding. 512 * 513 * Later in the function, if the message is short and there obviously 514 * cannot be this many blocks then variance_blocks can be reduced. */ 515 variance_blocks = is_sslv3 ? 2 : 6; 516 /* From now on we're dealing with the MAC, which conceptually has 13 517 * bytes of `header' before the start of the data (TLS) or 71/75 bytes 518 * (SSLv3) */ 519 len = data_plus_mac_plus_padding_size + header_length; 520 /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including 521 * |header|, assuming that there's no padding. */ 522 max_mac_bytes = len - md_size - 1; 523 /* num_blocks is the maximum number of hash blocks. */ 524 num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size; 525 /* In order to calculate the MAC in constant time we have to handle 526 * the final blocks specially because the padding value could cause the 527 * end to appear somewhere in the final |variance_blocks| blocks and we 528 * can't leak where. However, |num_starting_blocks| worth of data can 529 * be hashed right away because no padding value can affect whether 530 * they are plaintext. */ 531 num_starting_blocks = 0; 532 /* k is the starting byte offset into the conceptual header||data where 533 * we start processing. */ 534 k = 0; 535 /* mac_end_offset is the index just past the end of the data to be 536 * MACed. */ 537 mac_end_offset = data_plus_mac_size + header_length - md_size; 538 /* c is the index of the 0x80 byte in the final hash block that 539 * contains application data. */ 540 c = mac_end_offset % md_block_size; 541 /* index_a is the hash block number that contains the 0x80 terminating 542 * value. */ 543 index_a = mac_end_offset / md_block_size; 544 /* index_b is the hash block number that contains the 64-bit hash 545 * length, in bits. */ 546 index_b = (mac_end_offset + md_length_size) / md_block_size; 547 /* bits is the hash-length in bits. It includes the additional hash 548 * block for the masked HMAC key, or whole of |header| in the case of 549 * SSLv3. */ 550 551 /* For SSLv3, if we're going to have any starting blocks then we need 552 * at least two because the header is larger than a single block. */ 553 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) 554 { 555 num_starting_blocks = num_blocks - variance_blocks; 556 k = md_block_size*num_starting_blocks; 557 } 558 559 bits = 8*mac_end_offset; 560 if (!is_sslv3) 561 { 562 /* Compute the initial HMAC block. For SSLv3, the padding and 563 * secret bytes are included in |header| because they take more 564 * than a single block. */ 565 bits += 8*md_block_size; 566 memset(hmac_pad, 0, md_block_size); 567 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad)); 568 memcpy(hmac_pad, mac_secret, mac_secret_length); 569 for (i = 0; i < md_block_size; i++) 570 hmac_pad[i] ^= 0x36; 571 572 md_transform(md_state.c, hmac_pad); 573 } 574 575 if (length_is_big_endian) 576 { 577 memset(length_bytes,0,md_length_size-4); 578 length_bytes[md_length_size-4] = (unsigned char)(bits>>24); 579 length_bytes[md_length_size-3] = (unsigned char)(bits>>16); 580 length_bytes[md_length_size-2] = (unsigned char)(bits>>8); 581 length_bytes[md_length_size-1] = (unsigned char)bits; 582 } 583 else 584 { 585 memset(length_bytes,0,md_length_size); 586 length_bytes[md_length_size-5] = (unsigned char)(bits>>24); 587 length_bytes[md_length_size-6] = (unsigned char)(bits>>16); 588 length_bytes[md_length_size-7] = (unsigned char)(bits>>8); 589 length_bytes[md_length_size-8] = (unsigned char)bits; 590 } 591 592 if (k > 0) 593 { 594 if (is_sslv3) 595 { 596 /* The SSLv3 header is larger than a single block. 597 * overhang is the number of bytes beyond a single 598 * block that the header consumes: either 7 bytes 599 * (SHA1) or 11 bytes (MD5). */ 600 unsigned overhang = header_length-md_block_size; 601 md_transform(md_state.c, header); 602 memcpy(first_block, header + md_block_size, overhang); 603 memcpy(first_block + overhang, data, md_block_size-overhang); 604 md_transform(md_state.c, first_block); 605 for (i = 1; i < k/md_block_size - 1; i++) 606 md_transform(md_state.c, data + md_block_size*i - overhang); 607 } 608 else 609 { 610 /* k is a multiple of md_block_size. */ 611 memcpy(first_block, header, 13); 612 memcpy(first_block+13, data, md_block_size-13); 613 md_transform(md_state.c, first_block); 614 for (i = 1; i < k/md_block_size; i++) 615 md_transform(md_state.c, data + md_block_size*i - 13); 616 } 617 } 618 619 memset(mac_out, 0, sizeof(mac_out)); 620 621 /* We now process the final hash blocks. For each block, we construct 622 * it in constant time. If the |i==index_a| then we'll include the 0x80 623 * bytes and zero pad etc. For each block we selectively copy it, in 624 * constant time, to |mac_out|. */ 625 for (i = num_starting_blocks; i <= num_starting_blocks+variance_blocks; i++) 626 { 627 unsigned char block[MAX_HASH_BLOCK_SIZE]; 628 unsigned char is_block_a = constant_time_eq_8(i, index_a); 629 unsigned char is_block_b = constant_time_eq_8(i, index_b); 630 for (j = 0; j < md_block_size; j++) 631 { 632 unsigned char b = 0, is_past_c, is_past_cp1; 633 if (k < header_length) 634 b = header[k]; 635 else if (k < data_plus_mac_plus_padding_size + header_length) 636 b = data[k-header_length]; 637 k++; 638 639 is_past_c = is_block_a & constant_time_ge_8(j, c); 640 is_past_cp1 = is_block_a & constant_time_ge_8(j, c+1); 641 /* If this is the block containing the end of the 642 * application data, and we are at the offset for the 643 * 0x80 value, then overwrite b with 0x80. */ 644 b = constant_time_select_8(is_past_c, 0x80, b); 645 /* If this the the block containing the end of the 646 * application data and we're past the 0x80 value then 647 * just write zero. */ 648 b = b&~is_past_cp1; 649 /* If this is index_b (the final block), but not 650 * index_a (the end of the data), then the 64-bit 651 * length didn't fit into index_a and we're having to 652 * add an extra block of zeros. */ 653 b &= ~is_block_b | is_block_a; 654 655 /* The final bytes of one of the blocks contains the 656 * length. */ 657 if (j >= md_block_size - md_length_size) 658 { 659 /* If this is index_b, write a length byte. */ 660 b = constant_time_select_8( 661 is_block_b, length_bytes[j-(md_block_size-md_length_size)], b); 662 } 663 block[j] = b; 664 } 665 666 md_transform(md_state.c, block); 667 md_final_raw(md_state.c, block); 668 /* If this is index_b, copy the hash value to |mac_out|. */ 669 for (j = 0; j < md_size; j++) 670 mac_out[j] |= block[j]&is_block_b; 671 } 672 673 EVP_MD_CTX_init(&md_ctx); 674 EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */); 675 if (is_sslv3) 676 { 677 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */ 678 memset(hmac_pad, 0x5c, sslv3_pad_length); 679 680 EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length); 681 EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length); 682 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 683 } 684 else 685 { 686 /* Complete the HMAC in the standard manner. */ 687 for (i = 0; i < md_block_size; i++) 688 hmac_pad[i] ^= 0x6a; 689 690 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 691 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 692 } 693 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 694 if (md_out_size) 695 *md_out_size = md_out_size_u; 696 EVP_MD_CTX_cleanup(&md_ctx); 697 } 698