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 /* 63 * MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's 64 * length field. (SHA-384/512 have 128-bit length.) 65 */ 66 #define MAX_HASH_BIT_COUNT_BYTES 16 67 68 /* 69 * MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support. 70 * Currently SHA-384/512 has a 128-byte block size and that's the largest 71 * supported by TLS.) 72 */ 73 #define MAX_HASH_BLOCK_SIZE 128 74 75 /*- 76 * ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC 77 * record in |rec| by updating |rec->length| in constant time. 78 * 79 * block_size: the block size of the cipher used to encrypt the record. 80 * returns: 81 * 0: (in non-constant time) if the record is publicly invalid. 82 * 1: if the padding was valid 83 * -1: otherwise. 84 */ 85 int ssl3_cbc_remove_padding(const SSL *s, 86 SSL3_RECORD *rec, 87 unsigned block_size, unsigned mac_size) 88 { 89 unsigned padding_length, good; 90 const unsigned overhead = 1 /* padding length byte */ + mac_size; 91 92 /* 93 * These lengths are all public so we can test them in non-constant time. 94 */ 95 if (overhead > rec->length) 96 return 0; 97 98 padding_length = rec->data[rec->length - 1]; 99 good = constant_time_ge(rec->length, padding_length + overhead); 100 /* SSLv3 requires that the padding is minimal. */ 101 good &= constant_time_ge(block_size, padding_length + 1); 102 padding_length = good & (padding_length + 1); 103 rec->length -= padding_length; 104 rec->type |= padding_length << 8; /* kludge: pass padding length */ 105 return constant_time_select_int(good, 1, -1); 106 } 107 108 /*- 109 * tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC 110 * record in |rec| in constant time and returns 1 if the padding is valid and 111 * -1 otherwise. It also removes any explicit IV from the start of the record 112 * without leaking any timing about whether there was enough space after the 113 * padding was removed. 114 * 115 * block_size: the block size of the cipher used to encrypt the record. 116 * returns: 117 * 0: (in non-constant time) if the record is publicly invalid. 118 * 1: if the padding was valid 119 * -1: otherwise. 120 */ 121 int tls1_cbc_remove_padding(const SSL *s, 122 SSL3_RECORD *rec, 123 unsigned block_size, unsigned mac_size) 124 { 125 unsigned padding_length, good, to_check, i; 126 const unsigned overhead = 1 /* padding length byte */ + mac_size; 127 /* Check if version requires explicit IV */ 128 if (s->version >= TLS1_1_VERSION || s->version == DTLS1_BAD_VER) { 129 /* 130 * These lengths are all public so we can test them in non-constant 131 * time. 132 */ 133 if (overhead + block_size > rec->length) 134 return 0; 135 /* We can now safely skip explicit IV */ 136 rec->data += block_size; 137 rec->input += block_size; 138 rec->length -= block_size; 139 } else if (overhead > rec->length) 140 return 0; 141 142 padding_length = rec->data[rec->length - 1]; 143 144 /* 145 * NB: if compression is in operation the first packet may not be of even 146 * length so the padding bug check cannot be performed. This bug 147 * workaround has been around since SSLeay so hopefully it is either 148 * fixed now or no buggy implementation supports compression [steve] 149 */ 150 if ((s->options & SSL_OP_TLS_BLOCK_PADDING_BUG) && !s->expand) { 151 /* First packet is even in size, so check */ 152 if ((CRYPTO_memcmp(s->s3->read_sequence, "\0\0\0\0\0\0\0\0", 8) == 0) && 153 !(padding_length & 1)) { 154 s->s3->flags |= TLS1_FLAGS_TLS_PADDING_BUG; 155 } 156 if ((s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) && padding_length > 0) { 157 padding_length--; 158 } 159 } 160 161 if (EVP_CIPHER_flags(s->enc_read_ctx->cipher) & EVP_CIPH_FLAG_AEAD_CIPHER) { 162 /* padding is already verified */ 163 rec->length -= padding_length + 1; 164 return 1; 165 } 166 167 good = constant_time_ge(rec->length, overhead + padding_length); 168 /* 169 * The padding consists of a length byte at the end of the record and 170 * then that many bytes of padding, all with the same value as the length 171 * byte. Thus, with the length byte included, there are i+1 bytes of 172 * padding. We can't check just |padding_length+1| bytes because that 173 * leaks decrypted information. Therefore we always have to check the 174 * maximum amount of padding possible. (Again, the length of the record 175 * is public information so we can use it.) 176 */ 177 to_check = 255; /* maximum amount of padding. */ 178 if (to_check > rec->length - 1) 179 to_check = rec->length - 1; 180 181 for (i = 0; i < to_check; i++) { 182 unsigned char mask = constant_time_ge_8(padding_length, i); 183 unsigned char b = rec->data[rec->length - 1 - i]; 184 /* 185 * The final |padding_length+1| bytes should all have the value 186 * |padding_length|. Therefore the XOR should be zero. 187 */ 188 good &= ~(mask & (padding_length ^ b)); 189 } 190 191 /* 192 * If any of the final |padding_length+1| bytes had the wrong value, one 193 * or more of the lower eight bits of |good| will be cleared. 194 */ 195 good = constant_time_eq(0xff, good & 0xff); 196 padding_length = good & (padding_length + 1); 197 rec->length -= padding_length; 198 rec->type |= padding_length << 8; /* kludge: pass padding length */ 199 200 return constant_time_select_int(good, 1, -1); 201 } 202 203 /*- 204 * ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in 205 * constant time (independent of the concrete value of rec->length, which may 206 * vary within a 256-byte window). 207 * 208 * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to 209 * this function. 210 * 211 * On entry: 212 * rec->orig_len >= md_size 213 * md_size <= EVP_MAX_MD_SIZE 214 * 215 * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with 216 * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into 217 * a single or pair of cache-lines, then the variable memory accesses don't 218 * actually affect the timing. CPUs with smaller cache-lines [if any] are 219 * not multi-core and are not considered vulnerable to cache-timing attacks. 220 */ 221 #define CBC_MAC_ROTATE_IN_PLACE 222 223 void ssl3_cbc_copy_mac(unsigned char *out, 224 const SSL3_RECORD *rec, 225 unsigned md_size, unsigned orig_len) 226 { 227 #if defined(CBC_MAC_ROTATE_IN_PLACE) 228 unsigned char rotated_mac_buf[64 + EVP_MAX_MD_SIZE]; 229 unsigned char *rotated_mac; 230 #else 231 unsigned char rotated_mac[EVP_MAX_MD_SIZE]; 232 #endif 233 234 /* 235 * mac_end is the index of |rec->data| just after the end of the MAC. 236 */ 237 unsigned mac_end = rec->length; 238 unsigned mac_start = mac_end - md_size; 239 /* 240 * scan_start contains the number of bytes that we can ignore because the 241 * MAC's position can only vary by 255 bytes. 242 */ 243 unsigned scan_start = 0; 244 unsigned i, j; 245 unsigned div_spoiler; 246 unsigned rotate_offset; 247 248 OPENSSL_assert(orig_len >= md_size); 249 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 250 251 #if defined(CBC_MAC_ROTATE_IN_PLACE) 252 rotated_mac = rotated_mac_buf + ((0 - (size_t)rotated_mac_buf) & 63); 253 #endif 254 255 /* This information is public so it's safe to branch based on it. */ 256 if (orig_len > md_size + 255 + 1) 257 scan_start = orig_len - (md_size + 255 + 1); 258 /* 259 * div_spoiler contains a multiple of md_size that is used to cause the 260 * modulo operation to be constant time. Without this, the time varies 261 * based on the amount of padding when running on Intel chips at least. 262 * The aim of right-shifting md_size is so that the compiler doesn't 263 * figure out that it can remove div_spoiler as that would require it to 264 * prove that md_size is always even, which I hope is beyond it. 265 */ 266 div_spoiler = md_size >> 1; 267 div_spoiler <<= (sizeof(div_spoiler) - 1) * 8; 268 rotate_offset = (div_spoiler + mac_start - scan_start) % md_size; 269 270 memset(rotated_mac, 0, md_size); 271 for (i = scan_start, j = 0; i < orig_len; i++) { 272 unsigned char mac_started = constant_time_ge_8(i, mac_start); 273 unsigned char mac_ended = constant_time_ge_8(i, mac_end); 274 unsigned char b = rec->data[i]; 275 rotated_mac[j++] |= b & mac_started & ~mac_ended; 276 j &= constant_time_lt(j, md_size); 277 } 278 279 /* Now rotate the MAC */ 280 #if defined(CBC_MAC_ROTATE_IN_PLACE) 281 j = 0; 282 for (i = 0; i < md_size; i++) { 283 /* in case cache-line is 32 bytes, touch second line */ 284 ((volatile unsigned char *)rotated_mac)[rotate_offset ^ 32]; 285 out[j++] = rotated_mac[rotate_offset++]; 286 rotate_offset &= constant_time_lt(rotate_offset, md_size); 287 } 288 #else 289 memset(out, 0, md_size); 290 rotate_offset = md_size - rotate_offset; 291 rotate_offset &= constant_time_lt(rotate_offset, md_size); 292 for (i = 0; i < md_size; i++) { 293 for (j = 0; j < md_size; j++) 294 out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset); 295 rotate_offset++; 296 rotate_offset &= constant_time_lt(rotate_offset, md_size); 297 } 298 #endif 299 } 300 301 /* 302 * u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in 303 * little-endian order. The value of p is advanced by four. 304 */ 305 #define u32toLE(n, p) \ 306 (*((p)++)=(unsigned char)(n), \ 307 *((p)++)=(unsigned char)(n>>8), \ 308 *((p)++)=(unsigned char)(n>>16), \ 309 *((p)++)=(unsigned char)(n>>24)) 310 311 /* 312 * These functions serialize the state of a hash and thus perform the 313 * standard "final" operation without adding the padding and length that such 314 * a function typically does. 315 */ 316 static void tls1_md5_final_raw(void *ctx, unsigned char *md_out) 317 { 318 MD5_CTX *md5 = ctx; 319 u32toLE(md5->A, md_out); 320 u32toLE(md5->B, md_out); 321 u32toLE(md5->C, md_out); 322 u32toLE(md5->D, md_out); 323 } 324 325 static void tls1_sha1_final_raw(void *ctx, unsigned char *md_out) 326 { 327 SHA_CTX *sha1 = ctx; 328 l2n(sha1->h0, md_out); 329 l2n(sha1->h1, md_out); 330 l2n(sha1->h2, md_out); 331 l2n(sha1->h3, md_out); 332 l2n(sha1->h4, md_out); 333 } 334 335 #define LARGEST_DIGEST_CTX SHA_CTX 336 337 #ifndef OPENSSL_NO_SHA256 338 static void tls1_sha256_final_raw(void *ctx, unsigned char *md_out) 339 { 340 SHA256_CTX *sha256 = ctx; 341 unsigned i; 342 343 for (i = 0; i < 8; i++) { 344 l2n(sha256->h[i], md_out); 345 } 346 } 347 348 # undef LARGEST_DIGEST_CTX 349 # define LARGEST_DIGEST_CTX SHA256_CTX 350 #endif 351 352 #ifndef OPENSSL_NO_SHA512 353 static void tls1_sha512_final_raw(void *ctx, unsigned char *md_out) 354 { 355 SHA512_CTX *sha512 = ctx; 356 unsigned i; 357 358 for (i = 0; i < 8; i++) { 359 l2n8(sha512->h[i], md_out); 360 } 361 } 362 363 # undef LARGEST_DIGEST_CTX 364 # define LARGEST_DIGEST_CTX SHA512_CTX 365 #endif 366 367 /* 368 * ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function 369 * which ssl3_cbc_digest_record supports. 370 */ 371 char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx) 372 { 373 #ifdef OPENSSL_FIPS 374 if (FIPS_mode()) 375 return 0; 376 #endif 377 switch (EVP_MD_CTX_type(ctx)) { 378 case NID_md5: 379 case NID_sha1: 380 #ifndef OPENSSL_NO_SHA256 381 case NID_sha224: 382 case NID_sha256: 383 #endif 384 #ifndef OPENSSL_NO_SHA512 385 case NID_sha384: 386 case NID_sha512: 387 #endif 388 return 1; 389 default: 390 return 0; 391 } 392 } 393 394 /*- 395 * ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS 396 * record. 397 * 398 * ctx: the EVP_MD_CTX from which we take the hash function. 399 * ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX. 400 * md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written. 401 * md_out_size: if non-NULL, the number of output bytes is written here. 402 * header: the 13-byte, TLS record header. 403 * data: the record data itself, less any preceeding explicit IV. 404 * data_plus_mac_size: the secret, reported length of the data and MAC 405 * once the padding has been removed. 406 * data_plus_mac_plus_padding_size: the public length of the whole 407 * record, including padding. 408 * is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS. 409 * 410 * On entry: by virtue of having been through one of the remove_padding 411 * functions, above, we know that data_plus_mac_size is large enough to contain 412 * a padding byte and MAC. (If the padding was invalid, it might contain the 413 * padding too. ) 414 */ 415 void ssl3_cbc_digest_record(const EVP_MD_CTX *ctx, 416 unsigned char *md_out, 417 size_t *md_out_size, 418 const unsigned char header[13], 419 const unsigned char *data, 420 size_t data_plus_mac_size, 421 size_t data_plus_mac_plus_padding_size, 422 const unsigned char *mac_secret, 423 unsigned mac_secret_length, char is_sslv3) 424 { 425 union { 426 double align; 427 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; 428 } md_state; 429 void (*md_final_raw) (void *ctx, unsigned char *md_out); 430 void (*md_transform) (void *ctx, const unsigned char *block); 431 unsigned md_size, md_block_size = 64; 432 unsigned sslv3_pad_length = 40, header_length, variance_blocks, 433 len, max_mac_bytes, num_blocks, 434 num_starting_blocks, k, mac_end_offset, c, index_a, index_b; 435 unsigned int bits; /* at most 18 bits */ 436 unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES]; 437 /* hmac_pad is the masked HMAC key. */ 438 unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE]; 439 unsigned char first_block[MAX_HASH_BLOCK_SIZE]; 440 unsigned char mac_out[EVP_MAX_MD_SIZE]; 441 unsigned i, j, md_out_size_u; 442 EVP_MD_CTX md_ctx; 443 /* 444 * mdLengthSize is the number of bytes in the length field that 445 * terminates * the hash. 446 */ 447 unsigned md_length_size = 8; 448 char length_is_big_endian = 1; 449 450 /* 451 * This is a, hopefully redundant, check that allows us to forget about 452 * many possible overflows later in this function. 453 */ 454 OPENSSL_assert(data_plus_mac_plus_padding_size < 1024 * 1024); 455 456 switch (EVP_MD_CTX_type(ctx)) { 457 case NID_md5: 458 MD5_Init((MD5_CTX *)md_state.c); 459 md_final_raw = tls1_md5_final_raw; 460 md_transform = 461 (void (*)(void *ctx, const unsigned char *block))MD5_Transform; 462 md_size = 16; 463 sslv3_pad_length = 48; 464 length_is_big_endian = 0; 465 break; 466 case NID_sha1: 467 SHA1_Init((SHA_CTX *)md_state.c); 468 md_final_raw = tls1_sha1_final_raw; 469 md_transform = 470 (void (*)(void *ctx, const unsigned char *block))SHA1_Transform; 471 md_size = 20; 472 break; 473 #ifndef OPENSSL_NO_SHA256 474 case NID_sha224: 475 SHA224_Init((SHA256_CTX *)md_state.c); 476 md_final_raw = tls1_sha256_final_raw; 477 md_transform = 478 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform; 479 md_size = 224 / 8; 480 break; 481 case NID_sha256: 482 SHA256_Init((SHA256_CTX *)md_state.c); 483 md_final_raw = tls1_sha256_final_raw; 484 md_transform = 485 (void (*)(void *ctx, const unsigned char *block))SHA256_Transform; 486 md_size = 32; 487 break; 488 #endif 489 #ifndef OPENSSL_NO_SHA512 490 case NID_sha384: 491 SHA384_Init((SHA512_CTX *)md_state.c); 492 md_final_raw = tls1_sha512_final_raw; 493 md_transform = 494 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform; 495 md_size = 384 / 8; 496 md_block_size = 128; 497 md_length_size = 16; 498 break; 499 case NID_sha512: 500 SHA512_Init((SHA512_CTX *)md_state.c); 501 md_final_raw = tls1_sha512_final_raw; 502 md_transform = 503 (void (*)(void *ctx, const unsigned char *block))SHA512_Transform; 504 md_size = 64; 505 md_block_size = 128; 506 md_length_size = 16; 507 break; 508 #endif 509 default: 510 /* 511 * ssl3_cbc_record_digest_supported should have been called first to 512 * check that the hash function is supported. 513 */ 514 OPENSSL_assert(0); 515 if (md_out_size) 516 *md_out_size = -1; 517 return; 518 } 519 520 OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES); 521 OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE); 522 OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE); 523 524 header_length = 13; 525 if (is_sslv3) { 526 header_length = mac_secret_length + sslv3_pad_length + 8 /* sequence 527 * number */ + 528 1 /* record type */ + 529 2 /* record length */ ; 530 } 531 532 /* 533 * variance_blocks is the number of blocks of the hash that we have to 534 * calculate in constant time because they could be altered by the 535 * padding value. In SSLv3, the padding must be minimal so the end of 536 * the plaintext varies by, at most, 15+20 = 35 bytes. (We conservatively 537 * assume that the MAC size varies from 0..20 bytes.) In case the 9 bytes 538 * of hash termination (0x80 + 64-bit length) don't fit in the final 539 * block, we say that the final two blocks can vary based on the padding. 540 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not 541 * required to be minimal. Therefore we say that the final six blocks can 542 * vary based on the padding. Later in the function, if the message is 543 * short and there obviously cannot be this many blocks then 544 * variance_blocks can be reduced. 545 */ 546 variance_blocks = is_sslv3 ? 2 : 6; 547 /* 548 * From now on we're dealing with the MAC, which conceptually has 13 549 * bytes of `header' before the start of the data (TLS) or 71/75 bytes 550 * (SSLv3) 551 */ 552 len = data_plus_mac_plus_padding_size + header_length; 553 /* 554 * max_mac_bytes contains the maximum bytes of bytes in the MAC, 555 * including * |header|, assuming that there's no padding. 556 */ 557 max_mac_bytes = len - md_size - 1; 558 /* num_blocks is the maximum number of hash blocks. */ 559 num_blocks = 560 (max_mac_bytes + 1 + md_length_size + md_block_size - 561 1) / md_block_size; 562 /* 563 * In order to calculate the MAC in constant time we have to handle the 564 * final blocks specially because the padding value could cause the end 565 * to appear somewhere in the final |variance_blocks| blocks and we can't 566 * leak where. However, |num_starting_blocks| worth of data can be hashed 567 * right away because no padding value can affect whether they are 568 * plaintext. 569 */ 570 num_starting_blocks = 0; 571 /* 572 * k is the starting byte offset into the conceptual header||data where 573 * we start processing. 574 */ 575 k = 0; 576 /* 577 * mac_end_offset is the index just past the end of the data to be MACed. 578 */ 579 mac_end_offset = data_plus_mac_size + header_length - md_size; 580 /* 581 * c is the index of the 0x80 byte in the final hash block that contains 582 * application data. 583 */ 584 c = mac_end_offset % md_block_size; 585 /* 586 * index_a is the hash block number that contains the 0x80 terminating 587 * value. 588 */ 589 index_a = mac_end_offset / md_block_size; 590 /* 591 * index_b is the hash block number that contains the 64-bit hash length, 592 * in bits. 593 */ 594 index_b = (mac_end_offset + md_length_size) / md_block_size; 595 /* 596 * bits is the hash-length in bits. It includes the additional hash block 597 * for the masked HMAC key, or whole of |header| in the case of SSLv3. 598 */ 599 600 /* 601 * For SSLv3, if we're going to have any starting blocks then we need at 602 * least two because the header is larger than a single block. 603 */ 604 if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0)) { 605 num_starting_blocks = num_blocks - variance_blocks; 606 k = md_block_size * num_starting_blocks; 607 } 608 609 bits = 8 * mac_end_offset; 610 if (!is_sslv3) { 611 /* 612 * Compute the initial HMAC block. For SSLv3, the padding and secret 613 * bytes are included in |header| because they take more than a 614 * single block. 615 */ 616 bits += 8 * md_block_size; 617 memset(hmac_pad, 0, md_block_size); 618 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad)); 619 memcpy(hmac_pad, mac_secret, mac_secret_length); 620 for (i = 0; i < md_block_size; i++) 621 hmac_pad[i] ^= 0x36; 622 623 md_transform(md_state.c, hmac_pad); 624 } 625 626 if (length_is_big_endian) { 627 memset(length_bytes, 0, md_length_size - 4); 628 length_bytes[md_length_size - 4] = (unsigned char)(bits >> 24); 629 length_bytes[md_length_size - 3] = (unsigned char)(bits >> 16); 630 length_bytes[md_length_size - 2] = (unsigned char)(bits >> 8); 631 length_bytes[md_length_size - 1] = (unsigned char)bits; 632 } else { 633 memset(length_bytes, 0, md_length_size); 634 length_bytes[md_length_size - 5] = (unsigned char)(bits >> 24); 635 length_bytes[md_length_size - 6] = (unsigned char)(bits >> 16); 636 length_bytes[md_length_size - 7] = (unsigned char)(bits >> 8); 637 length_bytes[md_length_size - 8] = (unsigned char)bits; 638 } 639 640 if (k > 0) { 641 if (is_sslv3) { 642 unsigned overhang; 643 644 /* 645 * The SSLv3 header is larger than a single block. overhang is 646 * the number of bytes beyond a single block that the header 647 * consumes: either 7 bytes (SHA1) or 11 bytes (MD5). There are no 648 * ciphersuites in SSLv3 that are not SHA1 or MD5 based and 649 * therefore we can be confident that the header_length will be 650 * greater than |md_block_size|. However we add a sanity check just 651 * in case 652 */ 653 if (header_length <= md_block_size) { 654 /* Should never happen */ 655 return; 656 } 657 overhang = header_length - md_block_size; 658 md_transform(md_state.c, header); 659 memcpy(first_block, header + md_block_size, overhang); 660 memcpy(first_block + overhang, data, md_block_size - overhang); 661 md_transform(md_state.c, first_block); 662 for (i = 1; i < k / md_block_size - 1; i++) 663 md_transform(md_state.c, data + md_block_size * i - overhang); 664 } else { 665 /* k is a multiple of md_block_size. */ 666 memcpy(first_block, header, 13); 667 memcpy(first_block + 13, data, md_block_size - 13); 668 md_transform(md_state.c, first_block); 669 for (i = 1; i < k / md_block_size; i++) 670 md_transform(md_state.c, data + md_block_size * i - 13); 671 } 672 } 673 674 memset(mac_out, 0, sizeof(mac_out)); 675 676 /* 677 * We now process the final hash blocks. For each block, we construct it 678 * in constant time. If the |i==index_a| then we'll include the 0x80 679 * bytes and zero pad etc. For each block we selectively copy it, in 680 * constant time, to |mac_out|. 681 */ 682 for (i = num_starting_blocks; i <= num_starting_blocks + variance_blocks; 683 i++) { 684 unsigned char block[MAX_HASH_BLOCK_SIZE]; 685 unsigned char is_block_a = constant_time_eq_8(i, index_a); 686 unsigned char is_block_b = constant_time_eq_8(i, index_b); 687 for (j = 0; j < md_block_size; j++) { 688 unsigned char b = 0, is_past_c, is_past_cp1; 689 if (k < header_length) 690 b = header[k]; 691 else if (k < data_plus_mac_plus_padding_size + header_length) 692 b = data[k - header_length]; 693 k++; 694 695 is_past_c = is_block_a & constant_time_ge_8(j, c); 696 is_past_cp1 = is_block_a & constant_time_ge_8(j, c + 1); 697 /* 698 * If this is the block containing the end of the application 699 * data, and we are at the offset for the 0x80 value, then 700 * overwrite b with 0x80. 701 */ 702 b = constant_time_select_8(is_past_c, 0x80, b); 703 /* 704 * If this the the block containing the end of the application 705 * data and we're past the 0x80 value then just write zero. 706 */ 707 b = b & ~is_past_cp1; 708 /* 709 * If this is index_b (the final block), but not index_a (the end 710 * of the data), then the 64-bit length didn't fit into index_a 711 * and we're having to add an extra block of zeros. 712 */ 713 b &= ~is_block_b | is_block_a; 714 715 /* 716 * The final bytes of one of the blocks contains the length. 717 */ 718 if (j >= md_block_size - md_length_size) { 719 /* If this is index_b, write a length byte. */ 720 b = constant_time_select_8(is_block_b, 721 length_bytes[j - 722 (md_block_size - 723 md_length_size)], b); 724 } 725 block[j] = b; 726 } 727 728 md_transform(md_state.c, block); 729 md_final_raw(md_state.c, block); 730 /* If this is index_b, copy the hash value to |mac_out|. */ 731 for (j = 0; j < md_size; j++) 732 mac_out[j] |= block[j] & is_block_b; 733 } 734 735 EVP_MD_CTX_init(&md_ctx); 736 EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */ ); 737 if (is_sslv3) { 738 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */ 739 memset(hmac_pad, 0x5c, sslv3_pad_length); 740 741 EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length); 742 EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length); 743 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 744 } else { 745 /* Complete the HMAC in the standard manner. */ 746 for (i = 0; i < md_block_size; i++) 747 hmac_pad[i] ^= 0x6a; 748 749 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size); 750 EVP_DigestUpdate(&md_ctx, mac_out, md_size); 751 } 752 EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u); 753 if (md_out_size) 754 *md_out_size = md_out_size_u; 755 EVP_MD_CTX_cleanup(&md_ctx); 756 } 757 758 #ifdef OPENSSL_FIPS 759 760 /* 761 * Due to the need to use EVP in FIPS mode we can't reimplement digests but 762 * we can ensure the number of blocks processed is equal for all cases by 763 * digesting additional data. 764 */ 765 766 void tls_fips_digest_extra(const EVP_CIPHER_CTX *cipher_ctx, 767 EVP_MD_CTX *mac_ctx, const unsigned char *data, 768 size_t data_len, size_t orig_len) 769 { 770 size_t block_size, digest_pad, blocks_data, blocks_orig; 771 if (EVP_CIPHER_CTX_mode(cipher_ctx) != EVP_CIPH_CBC_MODE) 772 return; 773 block_size = EVP_MD_CTX_block_size(mac_ctx); 774 /*- 775 * We are in FIPS mode if we get this far so we know we have only SHA* 776 * digests and TLS to deal with. 777 * Minimum digest padding length is 17 for SHA384/SHA512 and 9 778 * otherwise. 779 * Additional header is 13 bytes. To get the number of digest blocks 780 * processed round up the amount of data plus padding to the nearest 781 * block length. Block length is 128 for SHA384/SHA512 and 64 otherwise. 782 * So we have: 783 * blocks = (payload_len + digest_pad + 13 + block_size - 1)/block_size 784 * equivalently: 785 * blocks = (payload_len + digest_pad + 12)/block_size + 1 786 * HMAC adds a constant overhead. 787 * We're ultimately only interested in differences so this becomes 788 * blocks = (payload_len + 29)/128 789 * for SHA384/SHA512 and 790 * blocks = (payload_len + 21)/64 791 * otherwise. 792 */ 793 digest_pad = block_size == 64 ? 21 : 29; 794 blocks_orig = (orig_len + digest_pad) / block_size; 795 blocks_data = (data_len + digest_pad) / block_size; 796 /* 797 * MAC enough blocks to make up the difference between the original and 798 * actual lengths plus one extra block to ensure this is never a no op. 799 * The "data" pointer should always have enough space to perform this 800 * operation as it is large enough for a maximum length TLS buffer. 801 */ 802 EVP_DigestSignUpdate(mac_ctx, data, 803 (blocks_orig - blocks_data + 1) * block_size); 804 } 805 #endif 806