mdw@git.distorted.org.uk Git - become/blob - src/crypt.c

   1 /* -*-c-*-
   2  *
   3  * $Id: crypt.c,v 1.2.2.1 1997/09/26 09:08:02 mdw Exp $
   4  *
   5  * Cryptographic transfer of `become' requests
   6  *
   7  * (c) 1997 EBI
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of `become'
  13  *
  14  * `Become' is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU General Public License as published by
  16  * the Free Software Foundation; either version 2 of the License, or
  17  * (at your option) any later version.
  18  *
  19  * `Become' is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU General Public License
  25  * along with `become'; if not, write to the Free Software Foundation,
  26  * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  27  */
  28
  29 /*----- Revision history --------------------------------------------------*
  30  *
  31  * $Log: crypt.c,v $
  32  * Revision 1.2.2.1  1997/09/26 09:08:02  mdw
  33  * Use the Blowfish encryption algorithm instead of IDEA.  This is partly
  34  * because I prefer Blowfish (without any particularly strong evidence) but
  35  * mainly because IDEA is patented and Blowfish isn't.
  36  *
  37  * Revision 1.2  1997/08/04 10:24:21  mdw
  38  * Sources placed under CVS control.
  39  *
  40  * Revision 1.1  1997/07/21  13:47:51  mdw
  41  * Initial revision
  42  *
  43  */
  44
  45 /*----- Header files ------------------------------------------------------*/
  46
  47 /* --- ANSI headers --- */
  48
  49 #include <ctype.h>
  50 #include <errno.h>
  51 #include <stdio.h>
  52 #include <stdlib.h>
  53 #include <string.h>
  54 #include <time.h>
  55
  56 /* --- Unix headers --- */
  57
  58 #include <sys/types.h>
  59 #include <sys/time.h>
  60 #include <unistd.h>
  61 #include <syslog.h>
  62 #include <fcntl.h>
  63
  64 /* --- Local headers --- */
  65
  66 #include "become.h"
  67 #include "blowfish.h"
  68 #include "config.h"
  69 #include "crypt.h"
  70 #include "icrypt.h"
  71 #include "md5.h"
  72 #include "noise.h"
  73 #include "rand.h"
  74 #include "tx.h"
  75 #include "utils.h"
  76
  77 /*----- Magic numbers -----------------------------------------------------*/
  78
  79 #define crypt__timeError 60             /* Seconds error to permit */
  80
  81 /*----- Main code ---------------------------------------------------------*/
  82
  83 /* --- @crypt__sessionKey@ --- *
  84  *
  85  * Arguments:   @const char *seedfile@ = pointer to name of seed file
  86  *              @unsigned char *k@ = our secret key
  87  *              @unsigned *sk@ = where to store the session key
  88  *              @unsigned char *iv@ = where to store the IV
  89  *
  90  * Returns:     ---
  91  *
  92  * Use:         Decides on a random session key and initialisation vector.
  93  */
  94
  95 static void crypt__sessionKey(const char *seedfile, unsigned char *k,
  96                               unsigned char *sk, unsigned char *iv)
  97 {
  98   FILE *fp;                             /* File handle for reading */
  99   struct flock l;
 100   int ok = 1;
 101
 102   /* --- Open the random seed file --- *
 103    *
 104    * If I can't manage that, create a new one.
 105    */
 106
 107   if ((fp = fopen(seedfile, "r+")) == 0) {
 108     ok = 0;
 109     if ((fp = fopen(seedfile, "w+")) == 0)
 110       die("can't create random number file: %s", strerror(errno));
 111     rand_clear();
 112   }
 113
 114   /* --- Lock the seed file against concurrency problems --- */
 115
 116   l.l_type = F_WRLCK;
 117   l.l_whence = SEEK_SET;
 118   l.l_start = 0;
 119   l.l_len = 0;
 120   if (fcntl(fileno(fp), F_SETLKW, &l) < 0)
 121     die("can't lock random number file: %s", strerror(errno));
 122
 123     /* --- Now read the file, and launder the seed --- */
 124
 125   if (ok)
 126     rand_read(fp);
 127
 128   /* --- Encrypt the pool using the secret key --- */
 129
 130   {
 131     icrypt_job j;
 132     icrypt_init(&j, k, BLOWFISH_KEYSIZE, 0);
 133     rand_encrypt(&j);
 134     burn(j);
 135   }
 136
 137   /* --- Generate the session key and IV --- */
 138
 139   noise_acquire();
 140   rand_extract(sk, BLOWFISH_KEYSIZE);
 141   rand_extract(iv, BLOWFISH_BLKSIZE);
 142
 143   IF_TRACING(TRACE_CRYPTO,
 144     traceblk(TRACE_CRYPTO, "crypto: session key:", sk, BLOWFISH_KEYSIZE);
 145     traceblk(TRACE_CRYPTO, "crypto: initialisation vector:",
 146              iv, BLOWFISH_BLKSIZE);
 147   );
 148
 149   /* --- Write the seed back --- */
 150
 151   rewind(fp);
 152   rand_write(fp);
 153   fclose(fp);
 154
 155 }
 156
 157 /* --- @crypt_packRequest@ --- *
 158  *
 159  * Arguments:   @request *rq@ = pointer to request block
 160  *              @unsigned char *buff@ = pointer to a buffer
 161  *              @time_t t@ = the current time
 162  *              @pid_t pid@ = my process ID
 163  *              @unsigned char *k@ = pointer to 128-bit key
 164  *              @unsigned char *sk@ = where to put the session key
 165  *
 166  * Returns:     ---
 167  *
 168  * Use:         Packs a request block into a buffer.  The buffer should have
 169  *              space for at least @crq_size@ bytes.  The buffer comes back
 170  *              encrypted and ready to send.
 171  */
 172
 173 void crypt_packRequest(request *rq, unsigned char *buff,
 174                        time_t t, pid_t pid,
 175                        unsigned char *k, unsigned char *sk)
 176 {
 177   /* --- First, build the easy stuff in the block --- */
 178
 179   buff[crq_cryptType] = cryptType_blowfish;
 180   store32(buff + crq_time, t);
 181   store32(buff + crq_pid, pid);
 182   store32(buff + crq_from, rq->from);
 183   store32(buff + crq_to, rq->to);
 184
 185   /* --- Now generate session keys and things --- */
 186
 187   crypt__sessionKey(file_RANDSEED, k, sk, buff + crq_iv);
 188   memcpy(buff + crq_session, sk, BLOWFISH_KEYSIZE);
 189
 190   /* --- The string causes a few problems --- *
 191    *
 192    * There's a good chance that the string will be a good deal shorter than
 193    * the space allowed for it.  This will probably mean lots of zeroes, and a
 194    * very easy known-plaintext job for a potential attacker.  (An early
 195    * version of this code used @strncpy@ which is even worse!)
 196    *
 197    * I'll fill the block with random (from @rand@(3) -- nothing too
 198    * elaborate) and then encrypt it using Blowfish in CFB mode, using the
 199    * first few bytes as the key.  This should provide a sufficiently
 200    * unpredictable background for the block.
 201    */
 202
 203   {
 204     icrypt_job j;
 205     unsigned char *p;
 206     unsigned u;
 207     md5 md;
 208     unsigned char qk[BLOWFISH_KEYSIZE];
 209
 210     /* --- Initialise the buffer with junk --- */
 211
 212     srand((unsigned int)(t ^ pid));     /* Seed the (bad) RNG */
 213     for (p = buff + crq_cmd; p < buff + crq_cmd + CMDLEN_MAX; p++) {
 214       u = rand(); *p = u ^ (u >> 8);
 215     }
 216
 217     /* --- Now make the junk a whole lot harder to predict --- */
 218
 219     p = buff + crq_cmd;
 220     md5_init(&md); md5_buffer(&md, p, CMDLEN_MAX); md5_final(&md, qk);
 221     icrypt_init(&j, qk, BLOWFISH_KEYSIZE, 0);
 222     icrypt_encrypt(&j, p, p, CMDLEN_MAX);
 223     burn(j); burn(qk); burn(md);
 224
 225     /* --- Copy the string into here --- */
 226
 227     strcpy((char *)buff + crq_cmd, rq->cmd);
 228   }
 229
 230   /* --- Checksum the finished data --- */
 231
 232   {
 233     md5 md;
 234     unsigned char mdbuf[MD5_HASHSIZE];
 235
 236     md5_init(&md);
 237     md5_buffer(&md, buff + crq_cipher, crq_check - crq_cipher);
 238     md5_final(&md, mdbuf);
 239     memcpy(buff + crq_check, mdbuf, 4);
 240     burn(md); burn(mdbuf);
 241   }
 242
 243   /* --- Encrypt the block --- *
 244    *
 245    * First, encrypt the session key using the master key.  Since the session
 246    * key is effectively random, this makes cracking the master key much
 247    * harder.  The rest of the block is then encrypted with the session key,
 248    * using the IV left over from encrypting the session key.
 249    */
 250
 251   {
 252     icrypt_job j;
 253
 254     T( traceblk(TRACE_CRYPTO, "crypto: plaintext request:",
 255                 buff, crq_size); )
 256
 257     T( traceblk(TRACE_CRYPTO, "crypto: master key:", k, BLOWFISH_KEYSIZE); )
 258     T( traceblk(TRACE_CRYPTO, "crypto: initial iv:",
 259                 buff + crq_iv, BLOWFISH_BLKSIZE); )
 260     T( traceblk(TRACE_CRYPTO, "crypto: session key:",
 261                 sk, BLOWFISH_KEYSIZE); )
 262
 263     icrypt_init(&j, k, BLOWFISH_KEYSIZE, buff + crq_iv);
 264
 265     icrypt_encrypt(&j, buff + crq_session,
 266                    buff + crq_session, BLOWFISH_KEYSIZE);
 267     T( traceblk(TRACE_CRYPTO, "crypto: encrypted session key:",
 268                 buff + crq_session, BLOWFISH_KEYSIZE); )
 269
 270     icrypt_reset(&j, sk, BLOWFISH_KEYSIZE, 0);
 271
 272     T( traceblk(TRACE_CRYPTO, "crypto: partial iv:",
 273                 j.iv, BLOWFISH_BLKSIZE); )
 274
 275     icrypt_encrypt(&j, buff + crq_cipher,
 276                    buff + crq_cipher, crq_size - crq_cipher);
 277     burn(j);
 278
 279     T( traceblk(TRACE_CRYPTO, "crypto: ciphertext request:",
 280                 buff, crq_size); )
 281   }
 282 }
 283
 284 /* --- @crypt_unpackRequest@ --- *
 285  *
 286  * Arguments:   @reqest *rq@ = pointer to destination request block
 287  *              @unsigned char *buff@ = pointer to source buffer
 288  *              @unsigned char *k@ = pointer to encryption key
 289  *              @unsigned char *sk@ = pointer to where to store session key
 290  *              @unsigned char *rpl@ = where to start building reply
 291  *
 292  * Returns:     Nonzero if it was decrypted OK
 293  *
 294  * Use:         Decrypts and unpacks a request buffer.
 295  */
 296
 297 int crypt_unpackRequest(request *rq, unsigned char *buff,
 298                         unsigned char *k, unsigned char *sk,
 299                         unsigned char *rpl)
 300 {
 301   {
 302     /* --- Check the encryption format --- */
 303
 304     if (buff[crq_cryptType] != cryptType_blowfish)
 305       return (0);
 306   }
 307
 308   {
 309     /* --- First things first: decrypt the block --- */
 310
 311     icrypt_job j;
 312
 313     T( traceblk(TRACE_CRYPTO, "crypto: ciphertext request:",
 314                 buff, crq_size); )
 315
 316     T( traceblk(TRACE_CRYPTO, "crypto: master key:", k, BLOWFISH_KEYSIZE); )
 317     T( traceblk(TRACE_CRYPTO, "crypto: initial iv:",
 318                 buff + crq_iv, BLOWFISH_BLKSIZE); )
 319
 320     icrypt_init(&j, k, BLOWFISH_KEYSIZE, buff + crq_iv);
 321     T( traceblk(TRACE_CRYPTO, "crypto: job block:", &j, sizeof(j)); )
 322
 323     T( traceblk(TRACE_CRYPTO, "crypto: encrypted session key:",
 324                 buff + crq_session, BLOWFISH_KEYSIZE); )
 325     icrypt_decrypt(&j, buff + crq_session,
 326                    buff + crq_session, BLOWFISH_KEYSIZE);
 327     memcpy(sk, buff + crq_session, BLOWFISH_KEYSIZE);
 328     T( traceblk(TRACE_CRYPTO, "crypto: session key:",
 329                 sk, BLOWFISH_KEYSIZE); )
 330
 331     icrypt_reset(&j, sk, BLOWFISH_KEYSIZE, 0);
 332
 333     T( traceblk(TRACE_CRYPTO, "crypto: partial iv:",
 334                 j.iv, BLOWFISH_BLKSIZE); )
 335
 336     icrypt_decrypt(&j, buff + crq_cipher,
 337                    buff + crq_cipher, crq_size - crq_cipher);
 338     icrypt_saveIV(&j, rpl + crp_iv);
 339
 340     T( traceblk(TRACE_CRYPTO, "crypto: plaintext request:",
 341                 buff, crq_size); )
 342
 343     memset(buff + crq_session, 0, BLOWFISH_KEYSIZE); /* Burn, baby, burn */
 344     burn(j);
 345   }
 346
 347   {
 348     /* --- Check the validity of the data therein --- */
 349
 350     md5 md;
 351     unsigned char mdbuf[MD5_HASHSIZE];
 352
 353     md5_init(&md);
 354     md5_buffer(&md, buff + crq_cipher, crq_check - crq_cipher);
 355     md5_final(&md, mdbuf);
 356     if (memcmp(mdbuf, buff + crq_check, 4) != 0) {
 357       syslog(LOG_INFO, "packet rejected: bad checksum");
 358       T( trace(TRACE_CRYPTO, "crypto: bad checksum on incoming request"); )
 359       return (0);
 360     }
 361     burn(md); burn(mdbuf);
 362   }
 363
 364   {
 365     /* --- Extract fields from the block --- */
 366
 367     rq->from = load32(buff + crq_from);
 368     rq->to = load32(buff + crq_to);
 369     memcpy(rq->cmd, buff + crq_cmd, CMDLEN_MAX);
 370   }
 371
 372   {
 373     /* --- Fill in bits of the reply block --- */
 374
 375     long t = (long)time(0);
 376     long u = (long)load32(buff + crq_time);
 377
 378     if (t - u > crypt__timeError || u - t > crypt__timeError) {
 379       syslog(LOG_INFO, "packet rejected: bad time");
 380       T( trace(TRACE_CRYPTO, "crypto: bad time on incoming request"); )
 381       return (0);
 382     }
 383     memcpy(rpl + crp_time, buff + crq_time, 8);
 384   }
 385
 386   /* --- Done --- */
 387
 388   T( trace(TRACE_CRYPTO, "crypto: valid request received"); )
 389   return (1);
 390 }
 391
 392 /* --- @crypt_packReply@ --- *
 393  *
 394  * Arguments:   @char *buff@ = pointer to reply block
 395  *              @unsigned char *sk@ = pointer to session key
 396  *              @int answer@ = yes or no
 397  *
 398  * Returns:     ---
 399  *
 400  * Use:         Packs and encrypts a reply block.
 401  */
 402
 403 void crypt_packReply(unsigned char *buff, unsigned char *sk, int answer)
 404 {
 405   {
 406     /* --- Store the answer --- */
 407
 408     buff[crp_answer] = (answer != 0);
 409   }
 410
 411   {
 412     /* --- Build the checksum --- */
 413
 414     md5 md;
 415     unsigned char mdbuf[MD5_HASHSIZE];
 416
 417     md5_init(&md);
 418     md5_buffer(&md, buff + crp_cipher, crp_check - crp_cipher);
 419     md5_final(&md, mdbuf);
 420     memcpy(buff + crp_check, mdbuf, 4);
 421     burn(md); burn(mdbuf);
 422   }
 423
 424   {
 425     /* --- Encrypt the buffer --- */
 426
 427     icrypt_job j;
 428
 429     T( traceblk(TRACE_CRYPTO, "crypto: plaintext reply:", buff, crp_size); )
 430
 431     icrypt_init(&j, sk, BLOWFISH_KEYSIZE, buff + crp_iv);
 432     icrypt_encrypt(&j, buff + crp_cipher,
 433                    buff + crp_cipher, crp_size - crp_cipher);
 434     burn(j);
 435
 436     T( traceblk(TRACE_CRYPTO, "crypto: ciphertext reply:", buff, crp_size); )
 437   }
 438 }
 439
 440 /* --- @crypt_unpackReply@ --- *
 441  *
 442  * Arguments:   @unsigned char *buff@ = pointer to reply buffer
 443  *              @unsigned char *sk@ = pointer to session key
 444  *              @time_t t@ = time at which request was sent
 445  *              @pid_t pid@ = my process ID
 446  *
 447  * Returns:     >0 if request granted, zero if denied, <0 if reply rejected
 448  *
 449  * Use:         Unpacks a reply block, and informs the caller of the outcome.
 450  */
 451
 452 int crypt_unpackReply(unsigned char *buff, unsigned char *sk,
 453                       time_t t, pid_t pid)
 454 {
 455   {
 456     /* --- Decrypt my reply block --- */
 457
 458     icrypt_job j;
 459
 460     T( traceblk(TRACE_CRYPTO, "crypto: ciphertext reply:", buff, crp_size); )
 461
 462     icrypt_init(&j, sk, BLOWFISH_KEYSIZE, buff + crp_iv);
 463     icrypt_decrypt(&j, buff + crp_cipher,
 464                    buff + crp_cipher, crp_size - crp_cipher);
 465     burn(j);
 466
 467     T( traceblk(TRACE_CRYPTO, "crypto: plaintext reply:", buff, crp_size); )
 468   }
 469
 470   {
 471     /* --- Check validity --- */
 472
 473     md5 md;
 474     unsigned char mdbuf[MD5_HASHSIZE];
 475     char b[8];
 476
 477     /* --- Check the checksum --- */
 478
 479     md5_init(&md);
 480     md5_buffer(&md, buff + crp_cipher, crp_check - crp_cipher);
 481     md5_final(&md, mdbuf);
 482     if (memcmp(buff + crp_check, mdbuf, 4) != 0) {
 483       syslog(LOG_INFO, "reply rejected: bad checksum");
 484       T( trace(TRACE_CRYPTO, "crypto: bad checksum on reply"); )
 485       return (-1);
 486     }
 487
 488     /* --- Check the identifier --- */
 489
 490     store32(b + 0, t); store32(b + 4, pid);
 491     if (memcmp(b, buff + crp_time, sizeof(b)) != 0) {
 492       syslog(LOG_INFO, "reply rejected: bad identification marker");
 493       T( trace(TRACE_CRYPTO, "crypto: bad id on reply"); )
 494       return (-1);
 495     }
 496   }
 497
 498   /* --- Return the value --- */
 499
 500   T( trace(TRACE_CRYPTO, "crypto: valid reply received"); )
 501   return (buff[crp_answer]);
 502 }
 503
 504 /*----- Test rig ----------------------------------------------------------*/
 505
 506 #ifdef TEST_RIG
 507
 508 int main(int argc, char *argv[])
 509 {
 510   unsigned char buff[8];
 511   unsigned char sk[BLOWFISH_KEYSIZE], k[BLOWFISH_KEYSIZE];
 512   FILE *fp;
 513
 514   ego(argv[0]);
 515   traceon(stdout, TRACE_CRYPTO);
 516   if (argc < 3)
 517     die("bad args");
 518   fp = fopen(argv[1], "r");
 519   if (!fp)
 520     die("fopen: %s", strerror(errno));
 521   tx_getBits(k, 128, fp);
 522   fclose(fp);
 523   crypt__sessionKey(argv[2], k, sk, buff);
 524   return (0);
 525 }
 526
 527 #endif
 528
 529 /*----- That's all, folks -------------------------------------------------*/