lib/gnutls_cipher.c

   1 /*
   2  * Copyright (C) 2000-2012 Free Software Foundation, Inc.
   3  *
   4  * Author: Nikos Mavrogiannopoulos
   5  *
   6  * This file is part of GnuTLS.
   7  *
   8  * The GnuTLS is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public License
  10  * as published by the Free Software Foundation; either version 3 of
  11  * the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful, but
  14  * WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public License
  19  * along with this program.  If not, see <http://www.gnu.org/licenses/>
  20  *
  21  */
  22
  23 /* Some high level functions to be used in the record encryption are
  24  * included here.
  25  */
  26
  27 #include "gnutls_int.h"
  28 #include "gnutls_errors.h"
  29 #include "gnutls_compress.h"
  30 #include "gnutls_cipher.h"
  31 #include "algorithms.h"
  32 #include "gnutls_hash_int.h"
  33 #include "gnutls_cipher_int.h"
  34 #include "debug.h"
  35 #include "gnutls_num.h"
  36 #include "gnutls_datum.h"
  37 #include "gnutls_kx.h"
  38 #include "gnutls_record.h"
  39 #include "gnutls_constate.h"
  40 #include <gnutls_state.h>
  41 #include <random.h>
  42
  43 static int compressed_to_ciphertext (gnutls_session_t session,
  44                                    uint8_t * cipher_data, int cipher_size,
  45                                    gnutls_datum_t *compressed,
  46                                    content_type_t _type,
  47                                    record_parameters_st * params);
  48 static int ciphertext_to_compressed (gnutls_session_t session,
  49                                    gnutls_datum_t *ciphertext,
  50                                    uint8_t * compress_data,
  51                                    int compress_size,
  52                                    uint8_t type,
  53                                    record_parameters_st * params, uint64* sequence);
  54
  55 inline static int
  56 is_write_comp_null (record_parameters_st * record_params)
  57 {
  58   if (record_params->compression_algorithm == GNUTLS_COMP_NULL)
  59     return 0;
  60
  61   return 1;
  62 }
  63
  64 inline static int
  65 is_read_comp_null (record_parameters_st * record_params)
  66 {
  67   if (record_params->compression_algorithm == GNUTLS_COMP_NULL)
  68     return 0;
  69
  70   return 1;
  71 }
  72
  73
  74 /* returns ciphertext which contains the headers too. This also
  75  * calculates the size in the header field.
  76  *
  77  * If random pad != 0 then the random pad data will be appended.
  78  */
  79 int
  80 _gnutls_encrypt (gnutls_session_t session, const uint8_t * headers,
  81                  size_t headers_size, const uint8_t * data,
  82                  size_t data_size, uint8_t * ciphertext,
  83                  size_t ciphertext_size, content_type_t type,
  84                  record_parameters_st * params)
  85 {
  86   gnutls_datum_t comp;
  87   int free_comp = 0;
  88   int ret;
  89
  90   if (data_size == 0 || is_write_comp_null (params) == 0)
  91     {
  92       comp.data = (uint8_t*)data;
  93       comp.size = data_size;
  94     }
  95   else
  96     {
  97       /* Here comp is allocated and must be
  98        * freed.
  99        */
 100       free_comp = 1;
 101
 102       comp.size = ciphertext_size - headers_size;
 103       comp.data = gnutls_malloc(comp.size);
 104       if (comp.data == NULL)
 105         return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);
 106
 107       ret = _gnutls_compress( &params->write.compression_state, data, data_size, comp.data, comp.size);
 108       if (ret < 0)
 109         {
 110           gnutls_free(comp.data);
 111           return gnutls_assert_val(ret);
 112         }
 113
 114       comp.size = ret;
 115     }
 116
 117   ret = compressed_to_ciphertext (session, &ciphertext[headers_size],
 118                                        ciphertext_size - headers_size,
 119                                        &comp, type, params);
 120
 121   if (free_comp)
 122     gnutls_free(comp.data);
 123
 124   if (ret < 0)
 125     return gnutls_assert_val(ret);
 126
 127   /* copy the headers */
 128   memcpy (ciphertext, headers, headers_size);
 129
 130   if(IS_DTLS(session))
 131     _gnutls_write_uint16 (ret, &ciphertext[11]);
 132   else
 133     _gnutls_write_uint16 (ret, &ciphertext[3]);
 134
 135   return ret + headers_size;
 136 }
 137
 138 /* Decrypts the given data.
 139  * Returns the decrypted data length.
 140  */
 141 int
 142 _gnutls_decrypt (gnutls_session_t session, uint8_t * ciphertext,
 143                  size_t ciphertext_size, uint8_t * data,
 144                  size_t max_data_size, content_type_t type,
 145                  record_parameters_st * params, uint64 *sequence)
 146 {
 147   gnutls_datum_t gcipher;
 148   int ret, data_size;
 149
 150   if (ciphertext_size == 0)
 151     return 0;
 152
 153   gcipher.size = ciphertext_size;
 154   gcipher.data = ciphertext;
 155
 156   if (is_read_comp_null (params) == 0)
 157     {
 158       ret =
 159         ciphertext_to_compressed (session, &gcipher, data, max_data_size,
 160                                    type, params, sequence);
 161       if (ret < 0)
 162         return gnutls_assert_val(ret);
 163
 164       return ret;
 165     }
 166   else
 167     {
 168       uint8_t* tmp_data;
 169
 170       tmp_data = gnutls_malloc(max_data_size);
 171       if (tmp_data == NULL)
 172         return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);
 173
 174       ret =
 175         ciphertext_to_compressed (session, &gcipher, tmp_data, max_data_size,
 176                                    type, params, sequence);
 177       if (ret < 0)
 178         goto leave;
 179
 180       data_size = ret;
 181
 182       if (ret != 0)
 183         {
 184           ret = _gnutls_decompress( &params->read.compression_state, tmp_data, data_size, data, max_data_size);
 185           if (ret < 0)
 186             goto leave;
 187         }
 188
 189 leave:
 190       gnutls_free(tmp_data);
 191       return ret;
 192     }
 193 }
 194
 195
 196 inline static int
 197 calc_enc_length (gnutls_session_t session, int data_size,
 198                  int hash_size, uint8_t * pad, int random_pad,
 199                  unsigned block_algo, unsigned auth_cipher, uint16_t blocksize)
 200 {
 201   uint8_t rnd;
 202   unsigned int length;
 203   int ret;
 204
 205   *pad = 0;
 206
 207   switch (block_algo)
 208     {
 209     case CIPHER_STREAM:
 210       length = data_size + hash_size;
 211       if (auth_cipher)
 212         length += AEAD_EXPLICIT_DATA_SIZE;
 213
 214       break;
 215     case CIPHER_BLOCK:
 216       ret = _gnutls_rnd (GNUTLS_RND_NONCE, &rnd, 1);
 217       if (ret < 0)
 218         return gnutls_assert_val(ret);
 219
 220       /* make rnd a multiple of blocksize */
 221       if (session->security_parameters.version == GNUTLS_SSL3 ||
 222           random_pad == 0)
 223         {
 224           rnd = 0;
 225         }
 226       else
 227         {
 228           rnd = (rnd / blocksize) * blocksize;
 229           /* added to avoid the case of pad calculated 0
 230            * seen below for pad calculation.
 231            */
 232           if (rnd > blocksize)
 233             rnd -= blocksize;
 234         }
 235
 236       length = data_size + hash_size;
 237
 238       *pad = (uint8_t) (blocksize - (length % blocksize)) + rnd;
 239
 240       length += *pad;
 241       if (_gnutls_version_has_explicit_iv
 242           (session->security_parameters.version))
 243         length += blocksize;    /* for the IV */
 244
 245       break;
 246     default:
 247       return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 248     }
 249
 250   return length;
 251 }
 252
 253 #define MAX_PREAMBLE_SIZE 16
 254
 255 /* generates the authentication data (data to be hashed only
 256  * and are not to be sent). Returns their size.
 257  */
 258 static inline int
 259 make_preamble (uint8_t * uint64_data, uint8_t type, unsigned int length,
 260                uint8_t ver, uint8_t * preamble)
 261 {
 262   uint8_t minor = _gnutls_version_get_minor (ver);
 263   uint8_t major = _gnutls_version_get_major (ver);
 264   uint8_t *p = preamble;
 265   uint16_t c_length;
 266
 267   c_length = _gnutls_conv_uint16 (length);
 268
 269   memcpy (p, uint64_data, 8);
 270   p += 8;
 271   *p = type;
 272   p++;
 273   if (ver != GNUTLS_SSL3)
 274     { /* TLS protocols */
 275       *p = major;
 276       p++;
 277       *p = minor;
 278       p++;
 279     }
 280   memcpy (p, &c_length, 2);
 281   p += 2;
 282   return p - preamble;
 283 }
 284
 285 /* This is the actual encryption
 286  * Encrypts the given compressed datum, and puts the result to cipher_data,
 287  * which has cipher_size size.
 288  * return the actual encrypted data length.
 289  */
 290 static int
 291 compressed_to_ciphertext (gnutls_session_t session,
 292                                uint8_t * cipher_data, int cipher_size,
 293                                gnutls_datum_t *compressed,
 294                                content_type_t type,
 295                                record_parameters_st * params)
 296 {
 297   uint8_t * tag_ptr = NULL;
 298   uint8_t pad;
 299   int length, length_to_encrypt, ret;
 300   uint8_t preamble[MAX_PREAMBLE_SIZE];
 301   int preamble_size;
 302   int tag_size = _gnutls_auth_cipher_tag_len (&params->write.cipher_state);
 303   int blocksize = gnutls_cipher_get_block_size (params->cipher_algorithm);
 304   unsigned block_algo =
 305     _gnutls_cipher_is_block (params->cipher_algorithm);
 306   uint8_t *data_ptr;
 307   int ver = gnutls_protocol_get_version (session);
 308   int explicit_iv = _gnutls_version_has_explicit_iv (session->security_parameters.version);
 309   int auth_cipher = _gnutls_auth_cipher_is_aead(&params->write.cipher_state);
 310   int random_pad;
 311
 312   /* We don't use long padding if requested or if we are in DTLS.
 313    */
 314   if (session->internals.priorities.no_padding == 0 && (!IS_DTLS(session)))
 315     random_pad = 1;
 316   else
 317     random_pad = 0;
 318
 319   _gnutls_hard_log("ENC[%p]: cipher: %s, MAC: %s, Epoch: %u\n",
 320     session, gnutls_cipher_get_name(params->cipher_algorithm), gnutls_mac_get_name(params->mac_algorithm),
 321     (unsigned int)params->epoch);
 322
 323   preamble_size =
 324     make_preamble (UINT64DATA
 325                    (params->write.sequence_number),
 326                    type, compressed->size, ver, preamble);
 327
 328   /* Calculate the encrypted length (padding etc.)
 329    */
 330   length_to_encrypt = length =
 331     calc_enc_length (session, compressed->size, tag_size, &pad,
 332                      random_pad, block_algo, auth_cipher, blocksize);
 333   if (length < 0)
 334     {
 335       return gnutls_assert_val(length);
 336     }
 337
 338   /* copy the encrypted data to cipher_data.
 339    */
 340   if (cipher_size < length)
 341     {
 342       return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);
 343     }
 344
 345   data_ptr = cipher_data;
 346
 347   if (explicit_iv)
 348     {
 349
 350       if (block_algo == CIPHER_BLOCK)
 351         {
 352           /* copy the random IV.
 353            */
 354           ret = _gnutls_rnd (GNUTLS_RND_NONCE, data_ptr, blocksize);
 355           if (ret < 0)
 356             return gnutls_assert_val(ret);
 357
 358           _gnutls_auth_cipher_setiv(&params->write.cipher_state, data_ptr, blocksize);
 359
 360           data_ptr += blocksize;
 361           cipher_data += blocksize;
 362           length_to_encrypt -= blocksize;
 363         }
 364       else if (auth_cipher)
 365         {
 366           uint8_t nonce[blocksize];
 367
 368           /* Values in AEAD are pretty fixed in TLS 1.2 for 128-bit block
 369            */
 370           if (params->write.IV.data == NULL || params->write.IV.size != AEAD_IMPLICIT_DATA_SIZE)
 371             return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 372
 373           /* Instead of generating a new nonce on every packet, we use the
 374            * write.sequence_number (It is a MAY on RFC 5288).
 375            */
 376           memcpy(nonce, params->write.IV.data, params->write.IV.size);
 377           memcpy(&nonce[AEAD_IMPLICIT_DATA_SIZE], UINT64DATA(params->write.sequence_number), 8);
 378
 379           _gnutls_auth_cipher_setiv(&params->write.cipher_state, nonce, AEAD_IMPLICIT_DATA_SIZE+AEAD_EXPLICIT_DATA_SIZE);
 380
 381           /* copy the explicit part */
 382           memcpy(data_ptr, &nonce[AEAD_IMPLICIT_DATA_SIZE], AEAD_EXPLICIT_DATA_SIZE);
 383
 384           data_ptr += AEAD_EXPLICIT_DATA_SIZE;
 385           cipher_data += AEAD_EXPLICIT_DATA_SIZE;
 386           /* In AEAD ciphers we don't encrypt the tag
 387            */
 388           length_to_encrypt -= AEAD_EXPLICIT_DATA_SIZE + tag_size;
 389         }
 390     }
 391   else
 392     {
 393       /* AEAD ciphers have an explicit IV. Shouldn't be used otherwise.
 394        */
 395       if (auth_cipher) return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 396     }
 397
 398   memcpy (data_ptr, compressed->data, compressed->size);
 399   data_ptr += compressed->size;
 400
 401   if (tag_size > 0)
 402     {
 403       tag_ptr = data_ptr;
 404       data_ptr += tag_size;
 405     }
 406   if (block_algo == CIPHER_BLOCK && pad > 0)
 407     {
 408       memset (data_ptr, pad - 1, pad);
 409     }
 410
 411   /* add the authenticate data */
 412   ret = _gnutls_auth_cipher_add_auth(&params->write.cipher_state, preamble, preamble_size);
 413   if (ret < 0)
 414     return gnutls_assert_val(ret);
 415
 416   /* Actual encryption (inplace).
 417    */
 418   ret =
 419     _gnutls_auth_cipher_encrypt2_tag (&params->write.cipher_state,
 420         cipher_data, length_to_encrypt,
 421         cipher_data, cipher_size,
 422         tag_ptr, tag_size, compressed->size);
 423   if (ret < 0)
 424     return gnutls_assert_val(ret);
 425
 426   return length;
 427 }
 428
 429
 430 /* Deciphers the ciphertext packet, and puts the result to compress_data, of compress_size.
 431  * Returns the actual compressed packet size.
 432  */
 433 static int
 434 ciphertext_to_compressed (gnutls_session_t session,
 435                           gnutls_datum_t *ciphertext,
 436                           uint8_t * compress_data,
 437                           int compress_size,
 438                           uint8_t type, record_parameters_st * params,
 439                           uint64* sequence)
 440 {
 441   uint8_t tag[MAX_HASH_SIZE];
 442   uint8_t pad;
 443   int length, length_to_decrypt;
 444   uint16_t blocksize;
 445   int ret, i, pad_failed = 0;
 446   uint8_t preamble[MAX_PREAMBLE_SIZE];
 447   unsigned int preamble_size;
 448   unsigned int ver = gnutls_protocol_get_version (session);
 449   unsigned int tag_size = _gnutls_auth_cipher_tag_len (&params->read.cipher_state);
 450   unsigned int explicit_iv = _gnutls_version_has_explicit_iv (session->security_parameters.version);
 451
 452   blocksize = gnutls_cipher_get_block_size (params->cipher_algorithm);
 453
 454   /* actual decryption (inplace)
 455    */
 456   switch (_gnutls_cipher_is_block (params->cipher_algorithm))
 457     {
 458     case CIPHER_STREAM:
 459       /* The way AEAD ciphers are defined in RFC5246, it allows
 460        * only stream ciphers.
 461        */
 462       if (explicit_iv && _gnutls_auth_cipher_is_aead(&params->read.cipher_state))
 463         {
 464           uint8_t nonce[blocksize];
 465           /* Values in AEAD are pretty fixed in TLS 1.2 for 128-bit block
 466            */
 467           if (params->read.IV.data == NULL || params->read.IV.size != 4)
 468             return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 469
 470           if (ciphertext->size < tag_size+AEAD_EXPLICIT_DATA_SIZE)
 471             return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
 472
 473           memcpy(nonce, params->read.IV.data, AEAD_IMPLICIT_DATA_SIZE);
 474           memcpy(&nonce[AEAD_IMPLICIT_DATA_SIZE], ciphertext->data, AEAD_EXPLICIT_DATA_SIZE);
 475
 476           _gnutls_auth_cipher_setiv(&params->read.cipher_state, nonce, AEAD_EXPLICIT_DATA_SIZE+AEAD_IMPLICIT_DATA_SIZE);
 477
 478           ciphertext->data += AEAD_EXPLICIT_DATA_SIZE;
 479           ciphertext->size -= AEAD_EXPLICIT_DATA_SIZE;
 480
 481           length_to_decrypt = ciphertext->size - tag_size;
 482         }
 483       else
 484         {
 485           if (ciphertext->size < tag_size)
 486             return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
 487
 488           length_to_decrypt = ciphertext->size;
 489         }
 490
 491       length = ciphertext->size - tag_size;
 492
 493       /* Pass the type, version, length and compressed through
 494        * MAC.
 495        */
 496       preamble_size =
 497         make_preamble (UINT64DATA(*sequence), type,
 498                        length, ver, preamble);
 499
 500       ret = _gnutls_auth_cipher_add_auth (&params->read.cipher_state, preamble, preamble_size);
 501       if (ret < 0)
 502         return gnutls_assert_val(ret);
 503
 504       if ((ret =
 505            _gnutls_auth_cipher_decrypt2 (&params->read.cipher_state,
 506              ciphertext->data, length_to_decrypt,
 507              ciphertext->data, ciphertext->size)) < 0)
 508         return gnutls_assert_val(ret);
 509
 510       break;
 511     case CIPHER_BLOCK:
 512       if (ciphertext->size < blocksize || (ciphertext->size % blocksize != 0))
 513         return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
 514
 515       /* ignore the IV in TLS 1.1+
 516        */
 517       if (explicit_iv)
 518         {
 519           _gnutls_auth_cipher_setiv(&params->read.cipher_state,
 520             ciphertext->data, blocksize);
 521
 522           ciphertext->size -= blocksize;
 523           ciphertext->data += blocksize;
 524         }
 525
 526       if (ciphertext->size < tag_size)
 527         return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
 528
 529       /* we don't use the auth_cipher interface here, since
 530        * TLS with block ciphers is impossible to be used under such
 531        * an API. (the length of plaintext is required to calculate
 532        * auth_data, but it is not available before decryption).
 533        */
 534       if ((ret =
 535            _gnutls_cipher_decrypt (&params->read.cipher_state.cipher,
 536              ciphertext->data, ciphertext->size)) < 0)
 537         return gnutls_assert_val(ret);
 538
 539       pad = ciphertext->data[ciphertext->size - 1] + 1;   /* pad */
 540
 541
 542       if ((int) pad > (int) ciphertext->size - tag_size)
 543         {
 544           gnutls_assert ();
 545           _gnutls_record_log
 546             ("REC[%p]: Short record length %d > %d - %d (under attack?)\n",
 547              session, pad, ciphertext->size, tag_size);
 548           /* We do not fail here. We check below for the
 549            * the pad_failed. If zero means success.
 550            */
 551           pad_failed = GNUTLS_E_DECRYPTION_FAILED;
 552           pad %= blocksize;
 553         }
 554
 555       length = ciphertext->size - tag_size - pad;
 556
 557       /* Check the pading bytes (TLS 1.x)
 558        */
 559       if (ver != GNUTLS_SSL3)
 560         for (i = 2; i < pad; i++)
 561           {
 562             if (ciphertext->data[ciphertext->size - i] !=
 563                 ciphertext->data[ciphertext->size - 1])
 564               pad_failed = GNUTLS_E_DECRYPTION_FAILED;
 565           }
 566
 567       if (length < 0)
 568         {
 569           /* Setting a proper length to prevent timing differences in
 570            * processing of records with invalid encryption.
 571            */
 572           length = ciphertext->size - tag_size;
 573         }
 574
 575       /* Pass the type, version, length and compressed through
 576        * MAC.
 577        */
 578       preamble_size =
 579         make_preamble (UINT64DATA(*sequence), type,
 580                        length, ver, preamble);
 581       ret = _gnutls_auth_cipher_add_auth (&params->read.cipher_state, preamble, preamble_size);
 582       if (ret < 0)
 583         return gnutls_assert_val(ret);
 584
 585       ret = _gnutls_auth_cipher_add_auth (&params->read.cipher_state, ciphertext->data, length);
 586       if (ret < 0)
 587         return gnutls_assert_val(ret);
 588
 589       break;
 590     default:
 591       return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 592     }
 593
 594   ret = _gnutls_auth_cipher_tag(&params->read.cipher_state, tag, tag_size);
 595   if (ret < 0)
 596     return gnutls_assert_val(ret);
 597
 598   /* This one was introduced to avoid a timing attack against the TLS
 599    * 1.0 protocol.
 600    */
 601   /* HMAC was not the same.
 602    */
 603   if (memcmp (tag, &ciphertext->data[length], tag_size) != 0 || pad_failed != 0)
 604     return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
 605
 606   /* copy the decrypted stuff to compress_data.
 607    */
 608   if (compress_size < length)
 609     return gnutls_assert_val(GNUTLS_E_DECOMPRESSION_FAILED);
 610
 611   if (compress_data != ciphertext->data)
 612     memcpy (compress_data, ciphertext->data, length);
 613
 614   return length;
 615 }