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,
 108                              comp.data, comp.size, session->internals.priorities.stateless_compression);
 109       if (ret < 0)
 110         {
 111           gnutls_free(comp.data);
 112           return gnutls_assert_val(ret);
 113         }
 114
 115       comp.size = ret;
 116     }
 117
 118   ret = compressed_to_ciphertext (session, &ciphertext[headers_size],
 119                                        ciphertext_size - headers_size,
 120                                        &comp, type, params);
 121
 122   if (free_comp)
 123     gnutls_free(comp.data);
 124
 125   if (ret < 0)
 126     return gnutls_assert_val(ret);
 127
 128   /* copy the headers */
 129   memcpy (ciphertext, headers, headers_size);
 130
 131   if(IS_DTLS(session))
 132     _gnutls_write_uint16 (ret, &ciphertext[11]);
 133   else
 134     _gnutls_write_uint16 (ret, &ciphertext[3]);
 135
 136   return ret + headers_size;
 137 }
 138
 139 /* Decrypts the given data.
 140  * Returns the decrypted data length.
 141  */
 142 int
 143 _gnutls_decrypt (gnutls_session_t session, uint8_t * ciphertext,
 144                  size_t ciphertext_size, uint8_t * data,
 145                  size_t max_data_size, content_type_t type,
 146                  record_parameters_st * params, uint64 *sequence)
 147 {
 148   gnutls_datum_t gcipher;
 149   int ret, data_size;
 150
 151   if (ciphertext_size == 0)
 152     return 0;
 153
 154   gcipher.size = ciphertext_size;
 155   gcipher.data = ciphertext;
 156
 157   if (is_read_comp_null (params) == 0)
 158     {
 159       ret =
 160         ciphertext_to_compressed (session, &gcipher, data, max_data_size,
 161                                    type, params, sequence);
 162       if (ret < 0)
 163         return gnutls_assert_val(ret);
 164
 165       return ret;
 166     }
 167   else
 168     {
 169       uint8_t* tmp_data;
 170
 171       tmp_data = gnutls_malloc(max_data_size);
 172       if (tmp_data == NULL)
 173         return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);
 174
 175       ret =
 176         ciphertext_to_compressed (session, &gcipher, tmp_data, max_data_size,
 177                                    type, params, sequence);
 178       if (ret < 0)
 179         goto leave;
 180
 181       data_size = ret;
 182
 183       if (ret != 0)
 184         {
 185           ret = _gnutls_decompress( &params->read.compression_state, tmp_data, data_size, data, max_data_size);
 186           if (ret < 0)
 187             goto leave;
 188         }
 189
 190 leave:
 191       gnutls_free(tmp_data);
 192       return ret;
 193     }
 194 }
 195
 196
 197 inline static int
 198 calc_enc_length_block (gnutls_session_t session, int data_size,
 199                  int hash_size, uint8_t * pad,
 200                  unsigned auth_cipher, uint16_t blocksize)
 201 {
 202   uint8_t rnd = *pad;
 203   unsigned int length;
 204
 205   *pad = 0;
 206
 207   /* make rnd a multiple of blocksize */
 208   if (session->security_parameters.version == GNUTLS_SSL3)
 209     {
 210       rnd = 0;
 211     }
 212
 213   if (rnd > 0)
 214     {
 215       rnd = (rnd / blocksize) * blocksize;
 216       /* added to avoid the case of pad calculated 0
 217        * seen below for pad calculation.
 218        */
 219       if (rnd > blocksize)
 220         rnd -= blocksize;
 221     }
 222
 223   length = data_size + hash_size;
 224
 225   *pad = (uint8_t) (blocksize - (length % blocksize)) + rnd;
 226
 227   length += *pad;
 228   if (_gnutls_version_has_explicit_iv
 229       (session->security_parameters.version))
 230     length += blocksize;    /* for the IV */
 231
 232   return length;
 233 }
 234
 235 inline static int
 236 calc_enc_length_stream (gnutls_session_t session, int data_size,
 237                  int hash_size, unsigned auth_cipher)
 238 {
 239   unsigned int length;
 240
 241   length = data_size + hash_size;
 242   if (auth_cipher)
 243     length += AEAD_EXPLICIT_DATA_SIZE;
 244
 245   return length;
 246 }
 247
 248 #define MAX_PREAMBLE_SIZE 16
 249
 250 /* generates the authentication data (data to be hashed only
 251  * and are not to be sent). Returns their size.
 252  */
 253 static inline int
 254 make_preamble (uint8_t * uint64_data, uint8_t type, unsigned int length,
 255                uint8_t ver, uint8_t * preamble)
 256 {
 257   uint8_t minor = _gnutls_version_get_minor (ver);
 258   uint8_t major = _gnutls_version_get_major (ver);
 259   uint8_t *p = preamble;
 260   uint16_t c_length;
 261
 262   c_length = _gnutls_conv_uint16 (length);
 263
 264   memcpy (p, uint64_data, 8);
 265   p += 8;
 266   *p = type;
 267   p++;
 268   if (ver != GNUTLS_SSL3)
 269     { /* TLS protocols */
 270       *p = major;
 271       p++;
 272       *p = minor;
 273       p++;
 274     }
 275   memcpy (p, &c_length, 2);
 276   p += 2;
 277   return p - preamble;
 278 }
 279
 280 /* This is the actual encryption
 281  * Encrypts the given compressed datum, and puts the result to cipher_data,
 282  * which has cipher_size size.
 283  * return the actual encrypted data length.
 284  */
 285 static int
 286 compressed_to_ciphertext (gnutls_session_t session,
 287                                uint8_t * cipher_data, int cipher_size,
 288                                gnutls_datum_t *compressed,
 289                                content_type_t type,
 290                                record_parameters_st * params)
 291 {
 292   uint8_t * tag_ptr = NULL;
 293   uint8_t pad = 0;
 294   int length, length_to_encrypt, ret;
 295   uint8_t preamble[MAX_PREAMBLE_SIZE];
 296   int preamble_size;
 297   int tag_size = _gnutls_auth_cipher_tag_len (&params->write.cipher_state);
 298   int blocksize = gnutls_cipher_get_block_size (params->cipher_algorithm);
 299   unsigned block_algo =
 300     _gnutls_cipher_is_block (params->cipher_algorithm);
 301   uint8_t *data_ptr;
 302   int ver = gnutls_protocol_get_version (session);
 303   int explicit_iv = _gnutls_version_has_explicit_iv (session->security_parameters.version);
 304   int auth_cipher = _gnutls_auth_cipher_is_aead(&params->write.cipher_state);
 305   uint8_t nonce[MAX_CIPHER_BLOCK_SIZE+1];
 306
 307
 308   _gnutls_hard_log("ENC[%p]: cipher: %s, MAC: %s, Epoch: %u\n",
 309     session, gnutls_cipher_get_name(params->cipher_algorithm), gnutls_mac_get_name(params->mac_algorithm),
 310     (unsigned int)params->epoch);
 311
 312   preamble_size =
 313     make_preamble (UINT64DATA
 314                    (params->write.sequence_number),
 315                    type, compressed->size, ver, preamble);
 316
 317   /* Calculate the encrypted length (padding etc.)
 318    */
 319   if (block_algo == CIPHER_BLOCK)
 320     {
 321       /* Call _gnutls_rnd() once. Get data used for the IV + 1 for
 322        * the random padding.
 323        */
 324       ret = _gnutls_rnd (GNUTLS_RND_NONCE, nonce, blocksize+1);
 325       if (ret < 0)
 326         return gnutls_assert_val(ret);
 327
 328       /* We don't use long padding if requested or if we are in DTLS.
 329        */
 330       if (session->internals.priorities.no_padding == 0 && !IS_DTLS(session))
 331         pad = nonce[blocksize];
 332
 333       length_to_encrypt = length =
 334         calc_enc_length_block (session, compressed->size, tag_size, &pad,
 335                                auth_cipher, blocksize);
 336     }
 337   else
 338     length_to_encrypt = length =
 339       calc_enc_length_stream (session, compressed->size, tag_size,
 340                              auth_cipher);
 341   if (length < 0)
 342     {
 343       return gnutls_assert_val(length);
 344     }
 345
 346   /* copy the encrypted data to cipher_data.
 347    */
 348   if (cipher_size < length)
 349     {
 350       return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);
 351     }
 352
 353   data_ptr = cipher_data;
 354
 355   if (explicit_iv)
 356     {
 357       if (block_algo == CIPHER_BLOCK)
 358         {
 359           /* copy the random IV.
 360            */
 361           memcpy(data_ptr, nonce, blocksize);
 362           _gnutls_auth_cipher_setiv(&params->write.cipher_state, data_ptr, blocksize);
 363
 364           data_ptr += blocksize;
 365           cipher_data += blocksize;
 366           length_to_encrypt -= blocksize;
 367         }
 368       else if (auth_cipher)
 369         {
 370           /* Values in AEAD are pretty fixed in TLS 1.2 for 128-bit block
 371            */
 372           if (params->write.IV.data == NULL || params->write.IV.size != AEAD_IMPLICIT_DATA_SIZE)
 373             return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 374
 375           /* Instead of generating a new nonce on every packet, we use the
 376            * write.sequence_number (It is a MAY on RFC 5288).
 377            */
 378           memcpy(nonce, params->write.IV.data, params->write.IV.size);
 379           memcpy(&nonce[AEAD_IMPLICIT_DATA_SIZE], UINT64DATA(params->write.sequence_number), 8);
 380
 381           _gnutls_auth_cipher_setiv(&params->write.cipher_state, nonce, AEAD_IMPLICIT_DATA_SIZE+AEAD_EXPLICIT_DATA_SIZE);
 382
 383           /* copy the explicit part */
 384           memcpy(data_ptr, &nonce[AEAD_IMPLICIT_DATA_SIZE], AEAD_EXPLICIT_DATA_SIZE);
 385
 386           data_ptr += AEAD_EXPLICIT_DATA_SIZE;
 387           cipher_data += AEAD_EXPLICIT_DATA_SIZE;
 388           /* In AEAD ciphers we don't encrypt the tag
 389            */
 390           length_to_encrypt -= AEAD_EXPLICIT_DATA_SIZE + tag_size;
 391         }
 392     }
 393   else
 394     {
 395       /* AEAD ciphers have an explicit IV. Shouldn't be used otherwise.
 396        */
 397       if (auth_cipher) return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 398     }
 399
 400   memcpy (data_ptr, compressed->data, compressed->size);
 401   data_ptr += compressed->size;
 402
 403   if (tag_size > 0)
 404     {
 405       tag_ptr = data_ptr;
 406       data_ptr += tag_size;
 407     }
 408   if (block_algo == CIPHER_BLOCK && pad > 0)
 409     {
 410       memset (data_ptr, pad - 1, pad);
 411     }
 412
 413   /* add the authenticate data */
 414   ret = _gnutls_auth_cipher_add_auth(&params->write.cipher_state, preamble, preamble_size);
 415   if (ret < 0)
 416     return gnutls_assert_val(ret);
 417
 418   /* Actual encryption (inplace).
 419    */
 420   ret =
 421     _gnutls_auth_cipher_encrypt2_tag (&params->write.cipher_state,
 422         cipher_data, length_to_encrypt,
 423         cipher_data, cipher_size,
 424         tag_ptr, tag_size, compressed->size);
 425   if (ret < 0)
 426     return gnutls_assert_val(ret);
 427
 428   return length;
 429 }
 430
 431
 432 /* Deciphers the ciphertext packet, and puts the result to compress_data, of compress_size.
 433  * Returns the actual compressed packet size.
 434  */
 435 static int
 436 ciphertext_to_compressed (gnutls_session_t session,
 437                           gnutls_datum_t *ciphertext,
 438                           uint8_t * compress_data,
 439                           int compress_size,
 440                           uint8_t type, record_parameters_st * params,
 441                           uint64* sequence)
 442 {
 443   uint8_t tag[MAX_HASH_SIZE];
 444   uint8_t pad;
 445   int length, length_to_decrypt;
 446   uint16_t blocksize;
 447   int ret, i, pad_failed = 0;
 448   uint8_t preamble[MAX_PREAMBLE_SIZE];
 449   unsigned int preamble_size;
 450   unsigned int ver = gnutls_protocol_get_version (session);
 451   unsigned int tag_size = _gnutls_auth_cipher_tag_len (&params->read.cipher_state);
 452   unsigned int explicit_iv = _gnutls_version_has_explicit_iv (session->security_parameters.version);
 453
 454   blocksize = gnutls_cipher_get_block_size (params->cipher_algorithm);
 455
 456   /* actual decryption (inplace)
 457    */
 458   switch (_gnutls_cipher_is_block (params->cipher_algorithm))
 459     {
 460     case CIPHER_STREAM:
 461       /* The way AEAD ciphers are defined in RFC5246, it allows
 462        * only stream ciphers.
 463        */
 464       if (explicit_iv && _gnutls_auth_cipher_is_aead(&params->read.cipher_state))
 465         {
 466           uint8_t nonce[blocksize];
 467           /* Values in AEAD are pretty fixed in TLS 1.2 for 128-bit block
 468            */
 469           if (params->read.IV.data == NULL || params->read.IV.size != 4)
 470             return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 471
 472           if (ciphertext->size < tag_size+AEAD_EXPLICIT_DATA_SIZE)
 473             return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
 474
 475           memcpy(nonce, params->read.IV.data, AEAD_IMPLICIT_DATA_SIZE);
 476           memcpy(&nonce[AEAD_IMPLICIT_DATA_SIZE], ciphertext->data, AEAD_EXPLICIT_DATA_SIZE);
 477
 478           _gnutls_auth_cipher_setiv(&params->read.cipher_state, nonce, AEAD_EXPLICIT_DATA_SIZE+AEAD_IMPLICIT_DATA_SIZE);
 479
 480           ciphertext->data += AEAD_EXPLICIT_DATA_SIZE;
 481           ciphertext->size -= AEAD_EXPLICIT_DATA_SIZE;
 482
 483           length_to_decrypt = ciphertext->size - tag_size;
 484         }
 485       else
 486         {
 487           if (ciphertext->size < tag_size)
 488             return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
 489
 490           length_to_decrypt = ciphertext->size;
 491         }
 492
 493       length = ciphertext->size - tag_size;
 494
 495       /* Pass the type, version, length and compressed through
 496        * MAC.
 497        */
 498       preamble_size =
 499         make_preamble (UINT64DATA(*sequence), type,
 500                        length, ver, preamble);
 501
 502       ret = _gnutls_auth_cipher_add_auth (&params->read.cipher_state, preamble, preamble_size);
 503       if (ret < 0)
 504         return gnutls_assert_val(ret);
 505
 506       if ((ret =
 507            _gnutls_auth_cipher_decrypt2 (&params->read.cipher_state,
 508              ciphertext->data, length_to_decrypt,
 509              ciphertext->data, ciphertext->size)) < 0)
 510         return gnutls_assert_val(ret);
 511
 512       break;
 513     case CIPHER_BLOCK:
 514       if (ciphertext->size < blocksize || (ciphertext->size % blocksize != 0))
 515         return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
 516
 517       /* ignore the IV in TLS 1.1+
 518        */
 519       if (explicit_iv)
 520         {
 521           _gnutls_auth_cipher_setiv(&params->read.cipher_state,
 522             ciphertext->data, blocksize);
 523
 524           ciphertext->size -= blocksize;
 525           ciphertext->data += blocksize;
 526         }
 527
 528       if (ciphertext->size < tag_size)
 529         return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
 530
 531       /* we don't use the auth_cipher interface here, since
 532        * TLS with block ciphers is impossible to be used under such
 533        * an API. (the length of plaintext is required to calculate
 534        * auth_data, but it is not available before decryption).
 535        */
 536       if ((ret =
 537            _gnutls_cipher_decrypt (&params->read.cipher_state.cipher,
 538              ciphertext->data, ciphertext->size)) < 0)
 539         return gnutls_assert_val(ret);
 540
 541       pad = ciphertext->data[ciphertext->size - 1] + 1;   /* pad */
 542
 543
 544       if ((int) pad > (int) ciphertext->size - tag_size)
 545         {
 546           gnutls_assert ();
 547           _gnutls_record_log
 548             ("REC[%p]: Short record length %d > %d - %d (under attack?)\n",
 549              session, pad, ciphertext->size, tag_size);
 550           /* We do not fail here. We check below for the
 551            * the pad_failed. If zero means success.
 552            */
 553           pad_failed = GNUTLS_E_DECRYPTION_FAILED;
 554           pad %= blocksize;
 555         }
 556
 557       length = ciphertext->size - tag_size - pad;
 558
 559       /* Check the pading bytes (TLS 1.x)
 560        */
 561       if (ver != GNUTLS_SSL3)
 562         for (i = 2; i < pad; i++)
 563           {
 564             if (ciphertext->data[ciphertext->size - i] !=
 565                 ciphertext->data[ciphertext->size - 1])
 566               pad_failed = GNUTLS_E_DECRYPTION_FAILED;
 567           }
 568
 569       if (length < 0)
 570         {
 571           /* Setting a proper length to prevent timing differences in
 572            * processing of records with invalid encryption.
 573            */
 574           length = ciphertext->size - tag_size;
 575         }
 576
 577       /* Pass the type, version, length and compressed through
 578        * MAC.
 579        */
 580       preamble_size =
 581         make_preamble (UINT64DATA(*sequence), type,
 582                        length, ver, preamble);
 583       ret = _gnutls_auth_cipher_add_auth (&params->read.cipher_state, preamble, preamble_size);
 584       if (ret < 0)
 585         return gnutls_assert_val(ret);
 586
 587       ret = _gnutls_auth_cipher_add_auth (&params->read.cipher_state, ciphertext->data, length);
 588       if (ret < 0)
 589         return gnutls_assert_val(ret);
 590
 591       break;
 592     default:
 593       return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
 594     }
 595
 596   ret = _gnutls_auth_cipher_tag(&params->read.cipher_state, tag, tag_size);
 597   if (ret < 0)
 598     return gnutls_assert_val(ret);
 599
 600   /* This one was introduced to avoid a timing attack against the TLS
 601    * 1.0 protocol.
 602    */
 603   /* HMAC was not the same.
 604    */
 605   if (memcmp (tag, &ciphertext->data[length], tag_size) != 0 || pad_failed != 0)
 606     return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
 607
 608   /* copy the decrypted stuff to compress_data.
 609    */
 610   if (compress_size < length)
 611     return gnutls_assert_val(GNUTLS_E_DECOMPRESSION_FAILED);
 612
 613   if (compress_data != ciphertext->data)
 614     memcpy (compress_data, ciphertext->data, length);
 615
 616   return length;
 617 }