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 "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. */
  80 static unsigned constant_time_lt(unsigned a, unsigned b)
  81         {
  82         a -= b;
  83         return DUPLICATE_MSB_TO_ALL(a);
  84         }
  85 
  86 /* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */
  87 static unsigned constant_time_ge(unsigned a, unsigned b)
  88         {
  89         a -= b;
  90         return DUPLICATE_MSB_TO_ALL(~a);
  91         }
  92 
  93 /* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */
  94 static unsigned char constant_time_eq_8(unsigned a, unsigned b)
  95         {
  96         unsigned c = a ^ b;
  97         c--;
  98         return DUPLICATE_MSB_TO_ALL_8(c);
  99         }
 100 
 101 /* ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC
 102  * record in |rec| by updating |rec->length| in constant time.
 103  *
 104  * block_size: the block size of the cipher used to encrypt the record.
 105  * returns:
 106  *   0: (in non-constant time) if the record is publicly invalid.
 107  *   1: if the padding was valid
 108  *  -1: otherwise. */
 109 int ssl3_cbc_remove_padding(const SSL* s,
 110                             SSL3_RECORD *rec,
 111                             unsigned block_size,
 112                             unsigned mac_size)
 113         {
 114         unsigned padding_length, good;
 115         const unsigned overhead = 1 /* padding length byte */ + mac_size;
 116 
 117         /* These lengths are all public so we can test them in non-constant
 118          * time. */
 119         if (overhead > rec->length)
 120                 return 0;
 121 
 122         padding_length = rec->data[rec->length-1];
 123         good = constant_time_ge(rec->length, padding_length+overhead);
 124         /* SSLv3 requires that the padding is minimal. */
 125         good &= constant_time_ge(block_size, padding_length+1);
 126         padding_length = good & (padding_length+1);
 127         rec->length -= padding_length;
 128         rec->type |= padding_length<<8;        /* kludge: pass padding length */
 129         return (int)((good & 1) | (~good & -1));
 130 }
 131 
 132 /* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
 133  * record in |rec| in constant time and returns 1 if the padding is valid and
 134  * -1 otherwise. It also removes any explicit IV from the start of the record
 135  * without leaking any timing about whether there was enough space after the
 136  * padding was removed.
 137  *
 138  * block_size: the block size of the cipher used to encrypt the record.
 139  * returns:
 140  *   0: (in non-constant time) if the record is publicly invalid.
 141  *   1: if the padding was valid
 142  *  -1: otherwise. */
 143 int tls1_cbc_remove_padding(const SSL* s,
 144                             SSL3_RECORD *rec,
 145                             unsigned block_size,
 146                             unsigned mac_size)
 147         {
 148         unsigned padding_length, good, to_check, i;
 149         const unsigned overhead = 1 /* padding length byte */ + mac_size;
 150         /* Check if version requires explicit IV */
 151         if (s->version >= TLS1_1_VERSION || s->version == DTLS1_BAD_VER)
 152                 {
 153                 /* These lengths are all public so we can test them in
 154                  * non-constant time.
 155                  */
 156                 if (overhead + block_size > rec->length)
 157                         return 0;
 158                 /* We can now safely skip explicit IV */
 159                 rec->data += block_size;
 160                 rec->input += block_size;
 161                 rec->length -= block_size;
 162                 }
 163         else if (overhead > rec->length)
 164                 return 0;
 165 
 166         padding_length = rec->data[rec->length-1];
 167 
 168         /* NB: if compression is in operation the first packet may not be of
 169          * even length so the padding bug check cannot be performed. This bug
 170          * workaround has been around since SSLeay so hopefully it is either
 171          * fixed now or no buggy implementation supports compression [steve]
 172          */
 173         if ( (s->options&SSL_OP_TLS_BLOCK_PADDING_BUG) && !s->expand)
 174                 {
 175                 /* First packet is even in size, so check */
 176                 if ((memcmp(s->s3->read_sequence, "\0\0\0\0\0\0\0\0",8) == 0) &&
 177                     !(padding_length & 1))
 178                         {
 179                         s->s3->flags|=TLS1_FLAGS_TLS_PADDING_BUG;
 180                         }
 181                 if ((s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) &&
 182                     padding_length > 0)
 183                         {
 184                         padding_length--;
 185                         }
 186                 }
 187 
 188         if (EVP_CIPHER_flags(s->enc_read_ctx->cipher)&EVP_CIPH_FLAG_AEAD_CIPHER)
 189                 {
 190                 /* padding is already verified */
 191                 rec->length -= padding_length + 1;
 192                 return 1;
 193                 }
 194 
 195         good = constant_time_ge(rec->length, overhead+padding_length);
 196         /* The padding consists of a length byte at the end of the record and
 197          * then that many bytes of padding, all with the same value as the
 198          * length byte. Thus, with the length byte included, there are i+1
 199          * bytes of padding.
 200          *
 201          * We can't check just |padding_length+1| bytes because that leaks
 202          * decrypted information. Therefore we always have to check the maximum
 203          * amount of padding possible. (Again, the length of the record is
 204          * public information so we can use it.) */
 205         to_check = 255; /* maximum amount of padding. */
 206         if (to_check > rec->length-1)
 207                 to_check = rec->length-1;
 208 
 209         for (i = 0; i < to_check; i++)
 210                 {
 211                 unsigned char mask = constant_time_ge(padding_length, i);
 212                 unsigned char b = rec->data[rec->length-1-i];
 213                 /* The final |padding_length+1| bytes should all have the value
 214                  * |padding_length|. Therefore the XOR should be zero. */
 215                 good &= ~(mask&(padding_length ^ b));
 216                 }
 217 
 218         /* If any of the final |padding_length+1| bytes had the wrong value,
 219          * one or more of the lower eight bits of |good| will be cleared. We
 220          * AND the bottom 8 bits together and duplicate the result to all the
 221          * bits. */
 222         good &= good >> 4;
 223         good &= good >> 2;
 224         good &= good >> 1;
 225         good <<= sizeof(good)*8-1;
 226         good = DUPLICATE_MSB_TO_ALL(good);
 227 
 228         padding_length = good & (padding_length+1);
 229         rec->length -= padding_length;
 230         rec->type |= padding_length<<8;        /* kludge: pass padding length */
 231 
 232         return (int)((good & 1) | (~good & -1));
 233         }
 234 
 235 /* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
 236  * constant time (independent of the concrete value of rec->length, which may
 237  * vary within a 256-byte window).
 238  *
 239  * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to
 240  * this function.
 241  *
 242  * On entry:
 243  *   rec->orig_len >= md_size
 244  *   md_size <= EVP_MAX_MD_SIZE
 245  *
 246  * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with
 247  * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into
 248  * a single or pair of cache-lines, then the variable memory accesses don't
 249  * actually affect the timing. CPUs with smaller cache-lines [if any] are
 250  * not multi-core and are not considered vulnerable to cache-timing attacks.
 251  */
 252 #define CBC_MAC_ROTATE_IN_PLACE
 253 
 254 void ssl3_cbc_copy_mac(unsigned char* out,
 255                        const SSL3_RECORD *rec,
 256                        unsigned md_size,unsigned orig_len)
 257         {
 258 #if defined(CBC_MAC_ROTATE_IN_PLACE)
 259         unsigned char rotated_mac_buf[64+EVP_MAX_MD_SIZE];
 260         unsigned char *rotated_mac;
 261 #else
 262         unsigned char rotated_mac[EVP_MAX_MD_SIZE];
 263 #endif
 264 
 265         /* mac_end is the index of |rec->data| just after the end of the MAC. */
 266         unsigned mac_end = rec->length;
 267         unsigned mac_start = mac_end - md_size;
 268         /* scan_start contains the number of bytes that we can ignore because
 269          * the MAC's position can only vary by 255 bytes. */
 270         unsigned scan_start = 0;
 271         unsigned i, j;
 272         unsigned div_spoiler;
 273         unsigned rotate_offset;
 274 
 275         OPENSSL_assert(orig_len >= md_size);
 276         OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
 277 
 278 #if defined(CBC_MAC_ROTATE_IN_PLACE)
 279         rotated_mac = rotated_mac_buf + ((0-(size_t)rotated_mac_buf)&63);
 280 #endif
 281 
 282         /* This information is public so it's safe to branch based on it. */
 283         if (orig_len > md_size + 255 + 1)
 284                 scan_start = orig_len - (md_size + 255 + 1);
 285         /* div_spoiler contains a multiple of md_size that is used to cause the
 286          * modulo operation to be constant time. Without this, the time varies
 287          * based on the amount of padding when running on Intel chips at least.
 288          *
 289          * The aim of right-shifting md_size is so that the compiler doesn't
 290          * figure out that it can remove div_spoiler as that would require it
 291          * to prove that md_size is always even, which I hope is beyond it. */
 292         div_spoiler = md_size >> 1;
 293         div_spoiler <<= (sizeof(div_spoiler)-1)*8;
 294         rotate_offset = (div_spoiler + mac_start - scan_start) % md_size;
 295 
 296         memset(rotated_mac, 0, md_size);
 297         for (i = scan_start, j = 0; i < orig_len; i++)
 298                 {
 299                 unsigned char mac_started = constant_time_ge(i, mac_start);
 300                 unsigned char mac_ended = constant_time_ge(i, mac_end);
 301                 unsigned char b = rec->data[i];
 302                 rotated_mac[j++] |= b & mac_started & ~mac_ended;
 303                 j &= constant_time_lt(j,md_size);
 304                 }
 305 
 306         /* Now rotate the MAC */
 307 #if defined(CBC_MAC_ROTATE_IN_PLACE)
 308         j = 0;
 309         for (i = 0; i < md_size; i++)
 310                 {
 311                 /* in case cache-line is 32 bytes, touch second line */
 312                 ((volatile unsigned char *)rotated_mac)[rotate_offset^32];
 313                 out[j++] = rotated_mac[rotate_offset++];
 314                 rotate_offset &= constant_time_lt(rotate_offset,md_size);
 315                 }
 316 #else
 317         memset(out, 0, md_size);
 318         rotate_offset = md_size - rotate_offset;
 319         rotate_offset &= constant_time_lt(rotate_offset,md_size);
 320         for (i = 0; i < md_size; i++)
 321                 {
 322                 for (j = 0; j < md_size; j++)
 323                         out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset);
 324                 rotate_offset++;
 325                 rotate_offset &= constant_time_lt(rotate_offset,md_size);
 326                 }
 327 #endif
 328         }
 329 
 330 /* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
 331  * little-endian order. The value of p is advanced by four. */
 332 #define u32toLE(n, p) \
 333         (*((p)++)=(unsigned char)(n), \
 334          *((p)++)=(unsigned char)(n>>8), \
 335          *((p)++)=(unsigned char)(n>>16), \
 336          *((p)++)=(unsigned char)(n>>24))
 337 
 338 /* These functions serialize the state of a hash and thus perform the standard
 339  * "final" operation without adding the padding and length that such a function
 340  * typically does. */
 341 static void tls1_md5_final_raw(void* ctx, unsigned char *md_out)
 342         {
 343         MD5_CTX *md5 = ctx;
 344         u32toLE(md5->A, md_out);
 345         u32toLE(md5->B, md_out);
 346         u32toLE(md5->C, md_out);
 347         u32toLE(md5->D, md_out);
 348         }
 349 
 350 static void tls1_sha1_final_raw(void* ctx, unsigned char *md_out)
 351         {
 352         SHA_CTX *sha1 = ctx;
 353         l2n(sha1->h0, md_out);
 354         l2n(sha1->h1, md_out);
 355         l2n(sha1->h2, md_out);
 356         l2n(sha1->h3, md_out);
 357         l2n(sha1->h4, md_out);
 358         }
 359 #define LARGEST_DIGEST_CTX SHA_CTX
 360 
 361 #ifndef OPENSSL_NO_SHA256
 362 static void tls1_sha256_final_raw(void* ctx, unsigned char *md_out)
 363         {
 364         SHA256_CTX *sha256 = ctx;
 365         unsigned i;
 366 
 367         for (i = 0; i < 8; i++)
 368                 {
 369                 l2n(sha256->h[i], md_out);
 370                 }
 371         }
 372 #undef  LARGEST_DIGEST_CTX
 373 #define LARGEST_DIGEST_CTX SHA256_CTX
 374 #endif
 375 
 376 #ifndef OPENSSL_NO_SHA512
 377 static void tls1_sha512_final_raw(void* ctx, unsigned char *md_out)
 378         {
 379         SHA512_CTX *sha512 = ctx;
 380         unsigned i;
 381 
 382         for (i = 0; i < 8; i++)
 383                 {
 384                 l2n8(sha512->h[i], md_out);
 385                 }
 386         }
 387 #undef  LARGEST_DIGEST_CTX
 388 #define LARGEST_DIGEST_CTX SHA512_CTX
 389 #endif
 390 
 391 /* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
 392  * which ssl3_cbc_digest_record supports. */
 393 char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx)
 394         {
 395 #ifdef OPENSSL_FIPS
 396         if (FIPS_mode())
 397                 return 0;
 398 #endif
 399         switch (EVP_MD_CTX_type(ctx))
 400                 {
 401                 case NID_md5:
 402                 case NID_sha1:
 403 #ifndef OPENSSL_NO_SHA256
 404                 case NID_sha224:
 405                 case NID_sha256:
 406 #endif
 407 #ifndef OPENSSL_NO_SHA512
 408                 case NID_sha384:
 409                 case NID_sha512:
 410 #endif
 411                         return 1;
 412                 default:
 413                         return 0;
 414                 }
 415         }
 416 
 417 /* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
 418  * record.
 419  *
 420  *   ctx: the EVP_MD_CTX from which we take the hash function.
 421  *     ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX.
 422  *   md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
 423  *   md_out_size: if non-NULL, the number of output bytes is written here.
 424  *   header: the 13-byte, TLS record header.
 425  *   data: the record data itself, less any preceeding explicit IV.
 426  *   data_plus_mac_size: the secret, reported length of the data and MAC
 427  *     once the padding has been removed.
 428  *   data_plus_mac_plus_padding_size: the public length of the whole
 429  *     record, including padding.
 430  *   is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS.
 431  *
 432  * On entry: by virtue of having been through one of the remove_padding
 433  * functions, above, we know that data_plus_mac_size is large enough to contain
 434  * a padding byte and MAC. (If the padding was invalid, it might contain the
 435  * padding too. ) */
 436 void ssl3_cbc_digest_record(
 437         const EVP_MD_CTX *ctx,
 438         unsigned char* md_out,
 439         size_t* md_out_size,
 440         const unsigned char header[13],
 441         const unsigned char *data,
 442         size_t data_plus_mac_size,
 443         size_t data_plus_mac_plus_padding_size,
 444         const unsigned char *mac_secret,
 445         unsigned mac_secret_length,
 446         char is_sslv3)
 447         {
 448         union { double align;
 449                 unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; } md_state;
 450         void (*md_final_raw)(void *ctx, unsigned char *md_out);
 451         void (*md_transform)(void *ctx, const unsigned char *block);
 452         unsigned md_size, md_block_size = 64;
 453         unsigned sslv3_pad_length = 40, header_length, variance_blocks,
 454                  len, max_mac_bytes, num_blocks,
 455                  num_starting_blocks, k, mac_end_offset, c, index_a, index_b;
 456         unsigned int bits;      /* at most 18 bits */
 457         unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES];
 458         /* hmac_pad is the masked HMAC key. */
 459         unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE];
 460         unsigned char first_block[MAX_HASH_BLOCK_SIZE];
 461         unsigned char mac_out[EVP_MAX_MD_SIZE];
 462         unsigned i, j, md_out_size_u;
 463         EVP_MD_CTX md_ctx;
 464         /* mdLengthSize is the number of bytes in the length field that terminates
 465         * the hash. */
 466         unsigned md_length_size = 8;
 467         char length_is_big_endian = 1;
 468 
 469         /* This is a, hopefully redundant, check that allows us to forget about
 470          * many possible overflows later in this function. */
 471         OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024);
 472 
 473         switch (EVP_MD_CTX_type(ctx))
 474                 {
 475                 case NID_md5:
 476                         MD5_Init((MD5_CTX*)md_state.c);
 477                         md_final_raw = tls1_md5_final_raw;
 478                         md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform;
 479                         md_size = 16;
 480                         sslv3_pad_length = 48;
 481                         length_is_big_endian = 0;
 482                         break;
 483                 case NID_sha1:
 484                         SHA1_Init((SHA_CTX*)md_state.c);
 485                         md_final_raw = tls1_sha1_final_raw;
 486                         md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform;
 487                         md_size = 20;
 488                         break;
 489 #ifndef OPENSSL_NO_SHA256
 490                 case NID_sha224:
 491                         SHA224_Init((SHA256_CTX*)md_state.c);
 492                         md_final_raw = tls1_sha256_final_raw;
 493                         md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform;
 494                         md_size = 224/8;
 495                         break;
 496                 case NID_sha256:
 497                         SHA256_Init((SHA256_CTX*)md_state.c);
 498                         md_final_raw = tls1_sha256_final_raw;
 499                         md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform;
 500                         md_size = 32;
 501                         break;
 502 #endif
 503 #ifndef OPENSSL_NO_SHA512
 504                 case NID_sha384:
 505                         SHA384_Init((SHA512_CTX*)md_state.c);
 506                         md_final_raw = tls1_sha512_final_raw;
 507                         md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform;
 508                         md_size = 384/8;
 509                         md_block_size = 128;
 510                         md_length_size = 16;
 511                         break;
 512                 case NID_sha512:
 513                         SHA512_Init((SHA512_CTX*)md_state.c);
 514                         md_final_raw = tls1_sha512_final_raw;
 515                         md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform;
 516                         md_size = 64;
 517                         md_block_size = 128;
 518                         md_length_size = 16;
 519                         break;
 520 #endif
 521                 default:
 522                         /* ssl3_cbc_record_digest_supported should have been
 523                          * called first to check that the hash function is
 524                          * supported. */
 525                         OPENSSL_assert(0);
 526                         if (md_out_size)
 527                                 *md_out_size = -1;
 528                         return;
 529                 }
 530 
 531         OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES);
 532         OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE);
 533         OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
 534 
 535         header_length = 13;
 536         if (is_sslv3)
 537                 {
 538                 header_length =
 539                         mac_secret_length +
 540                         sslv3_pad_length +
 541                         8 /* sequence number */ +
 542                         1 /* record type */ +
 543                         2 /* record length */;
 544                 }
 545 
 546         /* variance_blocks is the number of blocks of the hash that we have to
 547          * calculate in constant time because they could be altered by the
 548          * padding value.
 549          *
 550          * In SSLv3, the padding must be minimal so the end of the plaintext
 551          * varies by, at most, 15+20 = 35 bytes. (We conservatively assume that
 552          * the MAC size varies from 0..20 bytes.) In case the 9 bytes of hash
 553          * termination (0x80 + 64-bit length) don't fit in the final block, we
 554          * say that the final two blocks can vary based on the padding.
 555          *
 556          * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
 557          * required to be minimal. Therefore we say that the final six blocks
 558          * can vary based on the padding.
 559          *
 560          * Later in the function, if the message is short and there obviously
 561          * cannot be this many blocks then variance_blocks can be reduced. */
 562         variance_blocks = is_sslv3 ? 2 : 6;
 563         /* From now on we're dealing with the MAC, which conceptually has 13
 564          * bytes of `header' before the start of the data (TLS) or 71/75 bytes
 565          * (SSLv3) */
 566         len = data_plus_mac_plus_padding_size + header_length;
 567         /* max_mac_bytes contains the maximum bytes of bytes in the MAC, including
 568         * |header|, assuming that there's no padding. */
 569         max_mac_bytes = len - md_size - 1;
 570         /* num_blocks is the maximum number of hash blocks. */
 571         num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size;
 572         /* In order to calculate the MAC in constant time we have to handle
 573          * the final blocks specially because the padding value could cause the
 574          * end to appear somewhere in the final |variance_blocks| blocks and we
 575          * can't leak where. However, |num_starting_blocks| worth of data can
 576          * be hashed right away because no padding value can affect whether
 577          * they are plaintext. */
 578         num_starting_blocks = 0;
 579         /* k is the starting byte offset into the conceptual header||data where
 580          * we start processing. */
 581         k = 0;
 582         /* mac_end_offset is the index just past the end of the data to be
 583          * MACed. */
 584         mac_end_offset = data_plus_mac_size + header_length - md_size;
 585         /* c is the index of the 0x80 byte in the final hash block that
 586          * contains application data. */
 587         c = mac_end_offset % md_block_size;
 588         /* index_a is the hash block number that contains the 0x80 terminating
 589          * value. */
 590         index_a = mac_end_offset / md_block_size;
 591         /* index_b is the hash block number that contains the 64-bit hash
 592          * length, in bits. */
 593         index_b = (mac_end_offset + md_length_size) / md_block_size;
 594         /* bits is the hash-length in bits. It includes the additional hash
 595          * block for the masked HMAC key, or whole of |header| in the case of
 596          * SSLv3. */
 597 
 598         /* For SSLv3, if we're going to have any starting blocks then we need
 599          * at least two because the header is larger than a single block. */
 600         if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0))
 601                 {
 602                 num_starting_blocks = num_blocks - variance_blocks;
 603                 k = md_block_size*num_starting_blocks;
 604                 }
 605 
 606         bits = 8*mac_end_offset;
 607         if (!is_sslv3)
 608                 {
 609                 /* Compute the initial HMAC block. For SSLv3, the padding and
 610                  * secret bytes are included in |header| because they take more
 611                  * than a single block. */
 612                 bits += 8*md_block_size;
 613                 memset(hmac_pad, 0, md_block_size);
 614                 OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad));
 615                 memcpy(hmac_pad, mac_secret, mac_secret_length);
 616                 for (i = 0; i < md_block_size; i++)
 617                         hmac_pad[i] ^= 0x36;
 618 
 619                 md_transform(md_state.c, hmac_pad);
 620                 }
 621 
 622         if (length_is_big_endian)
 623                 {
 624                 memset(length_bytes,0,md_length_size-4);
 625                 length_bytes[md_length_size-4] = (unsigned char)(bits>>24);
 626                 length_bytes[md_length_size-3] = (unsigned char)(bits>>16);
 627                 length_bytes[md_length_size-2] = (unsigned char)(bits>>8);
 628                 length_bytes[md_length_size-1] = (unsigned char)bits;
 629                 }
 630         else
 631                 {
 632                 memset(length_bytes,0,md_length_size);
 633                 length_bytes[md_length_size-5] = (unsigned char)(bits>>24);
 634                 length_bytes[md_length_size-6] = (unsigned char)(bits>>16);
 635                 length_bytes[md_length_size-7] = (unsigned char)(bits>>8);
 636                 length_bytes[md_length_size-8] = (unsigned char)bits;
 637                 }
 638 
 639         if (k > 0)
 640                 {
 641                 if (is_sslv3)
 642                         {
 643                         /* The SSLv3 header is larger than a single block.
 644                          * overhang is the number of bytes beyond a single
 645                          * block that the header consumes: either 7 bytes
 646                          * (SHA1) or 11 bytes (MD5). */
 647                         unsigned overhang = header_length-md_block_size;
 648                         md_transform(md_state.c, header);
 649                         memcpy(first_block, header + md_block_size, overhang);
 650                         memcpy(first_block + overhang, data, md_block_size-overhang);
 651                         md_transform(md_state.c, first_block);
 652                         for (i = 1; i < k/md_block_size - 1; i++)
 653                                 md_transform(md_state.c, data + md_block_size*i - overhang);
 654                         }
 655                 else
 656                         {
 657                         /* k is a multiple of md_block_size. */
 658                         memcpy(first_block, header, 13);
 659                         memcpy(first_block+13, data, md_block_size-13);
 660                         md_transform(md_state.c, first_block);
 661                         for (i = 1; i < k/md_block_size; i++)
 662                                 md_transform(md_state.c, data + md_block_size*i - 13);
 663                         }
 664                 }
 665 
 666         memset(mac_out, 0, sizeof(mac_out));
 667 
 668         /* We now process the final hash blocks. For each block, we construct
 669          * it in constant time. If the |i==index_a| then we'll include the 0x80
 670          * bytes and zero pad etc. For each block we selectively copy it, in
 671          * constant time, to |mac_out|. */
 672         for (i = num_starting_blocks; i <= num_starting_blocks+variance_blocks; i++)
 673                 {
 674                 unsigned char block[MAX_HASH_BLOCK_SIZE];
 675                 unsigned char is_block_a = constant_time_eq_8(i, index_a);
 676                 unsigned char is_block_b = constant_time_eq_8(i, index_b);
 677                 for (j = 0; j < md_block_size; j++)
 678                         {
 679                         unsigned char b = 0, is_past_c, is_past_cp1;
 680                         if (k < header_length)
 681                                 b = header[k];
 682                         else if (k < data_plus_mac_plus_padding_size + header_length)
 683                                 b = data[k-header_length];
 684                         k++;
 685 
 686                         is_past_c = is_block_a & constant_time_ge(j, c);
 687                         is_past_cp1 = is_block_a & constant_time_ge(j, c+1);
 688                         /* If this is the block containing the end of the
 689                          * application data, and we are at the offset for the
 690                          * 0x80 value, then overwrite b with 0x80. */
 691                         b = (b&~is_past_c) | (0x80&is_past_c);
 692                         /* If this the the block containing the end of the
 693                          * application data and we're past the 0x80 value then
 694                          * just write zero. */
 695                         b = b&~is_past_cp1;
 696                         /* If this is index_b (the final block), but not
 697                          * index_a (the end of the data), then the 64-bit
 698                          * length didn't fit into index_a and we're having to
 699                          * add an extra block of zeros. */
 700                         b &= ~is_block_b | is_block_a;
 701 
 702                         /* The final bytes of one of the blocks contains the
 703                          * length. */
 704                         if (j >= md_block_size - md_length_size)
 705                                 {
 706                                 /* If this is index_b, write a length byte. */
 707                                 b = (b&~is_block_b) | (is_block_b&length_bytes[j-(md_block_size-md_length_size)]);
 708                                 }
 709                         block[j] = b;
 710                         }
 711 
 712                 md_transform(md_state.c, block);
 713                 md_final_raw(md_state.c, block);
 714                 /* If this is index_b, copy the hash value to |mac_out|. */
 715                 for (j = 0; j < md_size; j++)
 716                         mac_out[j] |= block[j]&is_block_b;
 717                 }
 718 
 719         EVP_MD_CTX_init(&md_ctx);
 720         EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */);
 721         if (is_sslv3)
 722                 {
 723                 /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
 724                 memset(hmac_pad, 0x5c, sslv3_pad_length);
 725 
 726                 EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length);
 727                 EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length);
 728                 EVP_DigestUpdate(&md_ctx, mac_out, md_size);
 729                 }
 730         else
 731                 {
 732                 /* Complete the HMAC in the standard manner. */
 733                 for (i = 0; i < md_block_size; i++)
 734                         hmac_pad[i] ^= 0x6a;
 735 
 736                 EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size);
 737                 EVP_DigestUpdate(&md_ctx, mac_out, md_size);
 738                 }
 739         EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
 740         if (md_out_size)
 741                 *md_out_size = md_out_size_u;
 742         EVP_MD_CTX_cleanup(&md_ctx);
 743         }
 744 
 745 #ifdef OPENSSL_FIPS
 746 
 747 /* Due to the need to use EVP in FIPS mode we can't reimplement digests but
 748  * we can ensure the number of blocks processed is equal for all cases
 749  * by digesting additional data.
 750  */
 751 
 752 void tls_fips_digest_extra(
 753         const EVP_CIPHER_CTX *cipher_ctx, EVP_MD_CTX *mac_ctx,
 754         const unsigned char *data, size_t data_len, size_t orig_len)
 755         {
 756         size_t block_size, digest_pad, blocks_data, blocks_orig;
 757         if (EVP_CIPHER_CTX_mode(cipher_ctx) != EVP_CIPH_CBC_MODE)
 758                 return;
 759         block_size = EVP_MD_CTX_block_size(mac_ctx);
 760         /* We are in FIPS mode if we get this far so we know we have only SHA*
 761          * digests and TLS to deal with.
 762          * Minimum digest padding length is 17 for SHA384/SHA512 and 9
 763          * otherwise.
 764          * Additional header is 13 bytes. To get the number of digest blocks
 765          * processed round up the amount of data plus padding to the nearest
 766          * block length. Block length is 128 for SHA384/SHA512 and 64 otherwise.
 767          * So we have:
 768          * blocks = (payload_len + digest_pad + 13 + block_size - 1)/block_size
 769          * equivalently:
 770          * blocks = (payload_len + digest_pad + 12)/block_size + 1
 771          * HMAC adds a constant overhead.
 772          * We're ultimately only interested in differences so this becomes
 773          * blocks = (payload_len + 29)/128
 774          * for SHA384/SHA512 and
 775          * blocks = (payload_len + 21)/64
 776          * otherwise.
 777          */
 778         digest_pad = block_size == 64 ? 21 : 29;
 779         blocks_orig = (orig_len + digest_pad)/block_size;
 780         blocks_data = (data_len + digest_pad)/block_size;
 781         /* MAC enough blocks to make up the difference between the original
 782          * and actual lengths plus one extra block to ensure this is never a
 783          * no op. The "data" pointer should always have enough space to
 784          * perform this operation as it is large enough for a maximum
 785          * length TLS buffer.
 786          */
 787         EVP_DigestSignUpdate(mac_ctx, data,
 788                                 (blocks_orig - blocks_data + 1) * block_size);
 789         }
 790 #endif