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