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

   1 /* -*-c-*-
   2  *
   3  * $Id: crypt.c,v 1.5 1998/06/18 15:08:49 mdw Exp $
   4  *
   5  * Cryptographic transfer of `become' requests
   6  *
   7  * (c) 1998 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 1.5  1998/06/18 15:08:49  mdw
  33  * Paranoia: set close-on-exec flag for seed file.
  34  *
  35  * Revision 1.4  1998/01/12 16:45:55  mdw
  36  * Fix copyright date.
  37  *
  38  * Revision 1.3  1997/09/26 09:14:58  mdw
  39  * Merged blowfish branch into trunk.
  40  *
  41  * Revision 1.2.2.1  1997/09/26 09:08:02  mdw
  42  * Use the Blowfish encryption algorithm instead of IDEA.  This is partly
  43  * because I prefer Blowfish (without any particularly strong evidence) but
  44  * mainly because IDEA is patented and Blowfish isn't.
  45  *
  46  * Revision 1.2  1997/08/04 10:24:21  mdw
  47  * Sources placed under CVS control.
  48  *
  49  * Revision 1.1  1997/07/21  13:47:51  mdw
  50  * Initial revision
  51  *
  52  */
  53
  54 /*----- Header files ------------------------------------------------------*/
  55
  56 /* --- ANSI headers --- */
  57
  58 #include <ctype.h>
  59 #include <errno.h>
  60 #include <stdio.h>
  61 #include <stdlib.h>
  62 #include <string.h>
  63 #include <time.h>
  64
  65 /* --- Unix headers --- */
  66
  67 #include <sys/types.h>
  68 #include <sys/time.h>
  69 #include <unistd.h>
  70 #include <syslog.h>
  71 #include <fcntl.h>
  72
  73 /* --- Local headers --- */
  74
  75 #include "become.h"
  76 #include "blowfish.h"
  77 #include "config.h"
  78 #include "crypt.h"
  79 #include "icrypt.h"
  80 #include "md5.h"
  81 #include "noise.h"
  82 #include "rand.h"
  83 #include "tx.h"
  84 #include "utils.h"
  85
  86 /*----- Magic numbers -----------------------------------------------------*/
  87
  88 #define crypt__timeError 60             /* Seconds error to permit */
  89
  90 /*----- Main code ---------------------------------------------------------*/
  91
  92 /* --- @crypt__sessionKey@ --- *
  93  *
  94  * Arguments:   @const char *seedfile@ = pointer to name of seed file
  95  *              @unsigned char *k@ = our secret key
  96  *              @unsigned *sk@ = where to store the session key
  97  *              @unsigned char *iv@ = where to store the IV
  98  *
  99  * Returns:     ---
 100  *
 101  * Use:         Decides on a random session key and initialisation vector.
 102  */
 103
 104 static void crypt__sessionKey(const char *seedfile, unsigned char *k,
 105                               unsigned char *sk, unsigned char *iv)
 106 {
 107   FILE *fp;                             /* File handle for reading */
 108   struct flock l;
 109   int ok = 1;
 110
 111   /* --- Open the random seed file --- *
 112    *
 113    * If I can't manage that, create a new one.
 114    */
 115
 116   if ((fp = fopen(seedfile, "r+")) == 0) {
 117     ok = 0;
 118     if ((fp = fopen(seedfile, "w+")) == 0)
 119       die("can't create random number file: %s", strerror(errno));
 120     rand_clear();
 121   }
 122   if (fcntl(fileno(fp), F_SETFD, 1) < 0) {
 123     die("can't set close-on-exec for random number file: %s",
 124         strerror(errno));
 125   }
 126
 127   /* --- Lock the seed file against concurrency problems --- */
 128
 129   l.l_type = F_WRLCK;
 130   l.l_whence = SEEK_SET;
 131   l.l_start = 0;
 132   l.l_len = 0;
 133   if (fcntl(fileno(fp), F_SETLKW, &l) < 0)
 134     die("can't lock random number file: %s", strerror(errno));
 135
 136     /* --- Now read the file, and launder the seed --- */
 137
 138   if (ok)
 139     rand_read(fp);
 140
 141   /* --- Encrypt the pool using the secret key --- */
 142
 143   {
 144     icrypt_job j;
 145     icrypt_init(&j, k, BLOWFISH_KEYSIZE, 0);
 146     rand_encrypt(&j);
 147     burn(j);
 148   }
 149
 150   /* --- Generate the session key and IV --- */
 151
 152   noise_acquire();
 153   rand_extract(sk, BLOWFISH_KEYSIZE);
 154   rand_extract(iv, BLOWFISH_BLKSIZE);
 155
 156   IF_TRACING(TRACE_CRYPTO,
 157     traceblk(TRACE_CRYPTO, "crypto: session key:", sk, BLOWFISH_KEYSIZE);
 158     traceblk(TRACE_CRYPTO, "crypto: initialisation vector:",
 159              iv, BLOWFISH_BLKSIZE);
 160   );
 161
 162   /* --- Write the seed back --- */
 163
 164   rewind(fp);
 165   rand_write(fp);
 166   fclose(fp);
 167
 168 }
 169
 170 /* --- @crypt_packRequest@ --- *
 171  *
 172  * Arguments:   @request *rq@ = pointer to request block
 173  *              @unsigned char *buff@ = pointer to a buffer
 174  *              @time_t t@ = the current time
 175  *              @pid_t pid@ = my process ID
 176  *              @unsigned char *k@ = pointer to 128-bit key
 177  *              @unsigned char *sk@ = where to put the session key
 178  *
 179  * Returns:     ---
 180  *
 181  * Use:         Packs a request block into a buffer.  The buffer should have
 182  *              space for at least @crq_size@ bytes.  The buffer comes back
 183  *              encrypted and ready to send.
 184  */
 185
 186 void crypt_packRequest(request *rq, unsigned char *buff,
 187                        time_t t, pid_t pid,
 188                        unsigned char *k, unsigned char *sk)
 189 {
 190   /* --- First, build the easy stuff in the block --- */
 191
 192   buff[crq_cryptType] = cryptType_blowfish;
 193   store32(buff + crq_time, t);
 194   store32(buff + crq_pid, pid);
 195   store32(buff + crq_from, rq->from);
 196   store32(buff + crq_to, rq->to);
 197
 198   /* --- Now generate session keys and things --- */
 199
 200   crypt__sessionKey(file_RANDSEED, k, sk, buff + crq_iv);
 201   memcpy(buff + crq_session, sk, BLOWFISH_KEYSIZE);
 202
 203   /* --- The string causes a few problems --- *
 204    *
 205    * There's a good chance that the string will be a good deal shorter than
 206    * the space allowed for it.  This will probably mean lots of zeroes, and a
 207    * very easy known-plaintext job for a potential attacker.  (An early
 208    * version of this code used @strncpy@ which is even worse!)
 209    *
 210    * I'll fill the block with random (from @rand@(3) -- nothing too
 211    * elaborate) and then encrypt it using Blowfish in CFB mode, using the
 212    * first few bytes as the key.  This should provide a sufficiently
 213    * unpredictable background for the block.
 214    */
 215
 216   {
 217     icrypt_job j;
 218     unsigned char *p;
 219     unsigned u;
 220     md5 md;
 221     unsigned char qk[BLOWFISH_KEYSIZE];
 222
 223     /* --- Initialise the buffer with junk --- */
 224
 225     srand((unsigned int)(t ^ pid));     /* Seed the (bad) RNG */
 226     for (p = buff + crq_cmd; p < buff + crq_cmd + CMDLEN_MAX; p++) {
 227       u = rand(); *p = u ^ (u >> 8);
 228     }
 229
 230     /* --- Now make the junk a whole lot harder to predict --- */
 231
 232     p = buff + crq_cmd;
 233     md5_init(&md); md5_buffer(&md, p, CMDLEN_MAX); md5_final(&md, qk);
 234     icrypt_init(&j, qk, BLOWFISH_KEYSIZE, 0);
 235     icrypt_encrypt(&j, p, p, CMDLEN_MAX);
 236     burn(j); burn(qk); burn(md);
 237
 238     /* --- Copy the string into here --- */
 239
 240     strcpy((char *)buff + crq_cmd, rq->cmd);
 241   }
 242
 243   /* --- Checksum the finished data --- */
 244
 245   {
 246     md5 md;
 247     unsigned char mdbuf[MD5_HASHSIZE];
 248
 249     md5_init(&md);
 250     md5_buffer(&md, buff + crq_cipher, crq_check - crq_cipher);
 251     md5_final(&md, mdbuf);
 252     memcpy(buff + crq_check, mdbuf, 4);
 253     burn(md); burn(mdbuf);
 254   }
 255
 256   /* --- Encrypt the block --- *
 257    *
 258    * First, encrypt the session key using the master key.  Since the session
 259    * key is effectively random, this makes cracking the master key much
 260    * harder.  The rest of the block is then encrypted with the session key,
 261    * using the IV left over from encrypting the session key.
 262    */
 263
 264   {
 265     icrypt_job j;
 266
 267     T( traceblk(TRACE_CRYPTO, "crypto: plaintext request:",
 268                 buff, crq_size); )
 269
 270     T( traceblk(TRACE_CRYPTO, "crypto: master key:", k, BLOWFISH_KEYSIZE); )
 271     T( traceblk(TRACE_CRYPTO, "crypto: initial iv:",
 272                 buff + crq_iv, BLOWFISH_BLKSIZE); )
 273     T( traceblk(TRACE_CRYPTO, "crypto: session key:",
 274                 sk, BLOWFISH_KEYSIZE); )
 275
 276     icrypt_init(&j, k, BLOWFISH_KEYSIZE, buff + crq_iv);
 277
 278     icrypt_encrypt(&j, buff + crq_session,
 279                    buff + crq_session, BLOWFISH_KEYSIZE);
 280     T( traceblk(TRACE_CRYPTO, "crypto: encrypted session key:",
 281                 buff + crq_session, BLOWFISH_KEYSIZE); )
 282
 283     icrypt_reset(&j, sk, BLOWFISH_KEYSIZE, 0);
 284
 285     T( traceblk(TRACE_CRYPTO, "crypto: partial iv:",
 286                 j.iv, BLOWFISH_BLKSIZE); )
 287
 288     icrypt_encrypt(&j, buff + crq_cipher,
 289                    buff + crq_cipher, crq_size - crq_cipher);
 290     burn(j);
 291
 292     T( traceblk(TRACE_CRYPTO, "crypto: ciphertext request:",
 293                 buff, crq_size); )
 294   }
 295 }
 296
 297 /* --- @crypt_unpackRequest@ --- *
 298  *
 299  * Arguments:   @reqest *rq@ = pointer to destination request block
 300  *              @unsigned char *buff@ = pointer to source buffer
 301  *              @unsigned char *k@ = pointer to encryption key
 302  *              @unsigned char *sk@ = pointer to where to store session key
 303  *              @unsigned char *rpl@ = where to start building reply
 304  *
 305  * Returns:     Nonzero if it was decrypted OK
 306  *
 307  * Use:         Decrypts and unpacks a request buffer.
 308  */
 309
 310 int crypt_unpackRequest(request *rq, unsigned char *buff,
 311                         unsigned char *k, unsigned char *sk,
 312                         unsigned char *rpl)
 313 {
 314   {
 315     /* --- Check the encryption format --- */
 316
 317     if (buff[crq_cryptType] != cryptType_blowfish)
 318       return (0);
 319   }
 320
 321   {
 322     /* --- First things first: decrypt the block --- */
 323
 324     icrypt_job j;
 325
 326     T( traceblk(TRACE_CRYPTO, "crypto: ciphertext request:",
 327                 buff, crq_size); )
 328
 329     T( traceblk(TRACE_CRYPTO, "crypto: master key:", k, BLOWFISH_KEYSIZE); )
 330     T( traceblk(TRACE_CRYPTO, "crypto: initial iv:",
 331                 buff + crq_iv, BLOWFISH_BLKSIZE); )
 332
 333     icrypt_init(&j, k, BLOWFISH_KEYSIZE, buff + crq_iv);
 334     T( traceblk(TRACE_CRYPTO, "crypto: job block:", &j, sizeof(j)); )
 335
 336     T( traceblk(TRACE_CRYPTO, "crypto: encrypted session key:",
 337                 buff + crq_session, BLOWFISH_KEYSIZE); )
 338     icrypt_decrypt(&j, buff + crq_session,
 339                    buff + crq_session, BLOWFISH_KEYSIZE);
 340     memcpy(sk, buff + crq_session, BLOWFISH_KEYSIZE);
 341     T( traceblk(TRACE_CRYPTO, "crypto: session key:",
 342                 sk, BLOWFISH_KEYSIZE); )
 343
 344     icrypt_reset(&j, sk, BLOWFISH_KEYSIZE, 0);
 345
 346     T( traceblk(TRACE_CRYPTO, "crypto: partial iv:",
 347                 j.iv, BLOWFISH_BLKSIZE); )
 348
 349     icrypt_decrypt(&j, buff + crq_cipher,
 350                    buff + crq_cipher, crq_size - crq_cipher);
 351     icrypt_saveIV(&j, rpl + crp_iv);
 352
 353     T( traceblk(TRACE_CRYPTO, "crypto: plaintext request:",
 354                 buff, crq_size); )
 355
 356     memset(buff + crq_session, 0, BLOWFISH_KEYSIZE); /* Burn, baby, burn */
 357     burn(j);
 358   }
 359
 360   {
 361     /* --- Check the validity of the data therein --- */
 362
 363     md5 md;
 364     unsigned char mdbuf[MD5_HASHSIZE];
 365
 366     md5_init(&md);
 367     md5_buffer(&md, buff + crq_cipher, crq_check - crq_cipher);
 368     md5_final(&md, mdbuf);
 369     if (memcmp(mdbuf, buff + crq_check, 4) != 0) {
 370       syslog(LOG_INFO, "packet rejected: bad checksum");
 371       T( trace(TRACE_CRYPTO, "crypto: bad checksum on incoming request"); )
 372       return (0);
 373     }
 374     burn(md); burn(mdbuf);
 375   }
 376
 377   {
 378     /* --- Extract fields from the block --- */
 379
 380     rq->from = load32(buff + crq_from);
 381     rq->to = load32(buff + crq_to);
 382     memcpy(rq->cmd, buff + crq_cmd, CMDLEN_MAX);
 383   }
 384
 385   {
 386     /* --- Fill in bits of the reply block --- */
 387
 388     long t = (long)time(0);
 389     long u = (long)load32(buff + crq_time);
 390
 391     if (t - u > crypt__timeError || u - t > crypt__timeError) {
 392       syslog(LOG_INFO, "packet rejected: bad time");
 393       T( trace(TRACE_CRYPTO, "crypto: bad time on incoming request"); )
 394       return (0);
 395     }
 396     memcpy(rpl + crp_time, buff + crq_time, 8);
 397   }
 398
 399   /* --- Done --- */
 400
 401   T( trace(TRACE_CRYPTO, "crypto: valid request received"); )
 402   return (1);
 403 }
 404
 405 /* --- @crypt_packReply@ --- *
 406  *
 407  * Arguments:   @char *buff@ = pointer to reply block
 408  *              @unsigned char *sk@ = pointer to session key
 409  *              @int answer@ = yes or no
 410  *
 411  * Returns:     ---
 412  *
 413  * Use:         Packs and encrypts a reply block.
 414  */
 415
 416 void crypt_packReply(unsigned char *buff, unsigned char *sk, int answer)
 417 {
 418   {
 419     /* --- Store the answer --- */
 420
 421     buff[crp_answer] = (answer != 0);
 422   }
 423
 424   {
 425     /* --- Build the checksum --- */
 426
 427     md5 md;
 428     unsigned char mdbuf[MD5_HASHSIZE];
 429
 430     md5_init(&md);
 431     md5_buffer(&md, buff + crp_cipher, crp_check - crp_cipher);
 432     md5_final(&md, mdbuf);
 433     memcpy(buff + crp_check, mdbuf, 4);
 434     burn(md); burn(mdbuf);
 435   }
 436
 437   {
 438     /* --- Encrypt the buffer --- */
 439
 440     icrypt_job j;
 441
 442     T( traceblk(TRACE_CRYPTO, "crypto: plaintext reply:", buff, crp_size); )
 443
 444     icrypt_init(&j, sk, BLOWFISH_KEYSIZE, buff + crp_iv);
 445     icrypt_encrypt(&j, buff + crp_cipher,
 446                    buff + crp_cipher, crp_size - crp_cipher);
 447     burn(j);
 448
 449     T( traceblk(TRACE_CRYPTO, "crypto: ciphertext reply:", buff, crp_size); )
 450   }
 451 }
 452
 453 /* --- @crypt_unpackReply@ --- *
 454  *
 455  * Arguments:   @unsigned char *buff@ = pointer to reply buffer
 456  *              @unsigned char *sk@ = pointer to session key
 457  *              @time_t t@ = time at which request was sent
 458  *              @pid_t pid@ = my process ID
 459  *
 460  * Returns:     >0 if request granted, zero if denied, <0 if reply rejected
 461  *
 462  * Use:         Unpacks a reply block, and informs the caller of the outcome.
 463  */
 464
 465 int crypt_unpackReply(unsigned char *buff, unsigned char *sk,
 466                       time_t t, pid_t pid)
 467 {
 468   {
 469     /* --- Decrypt my reply block --- */
 470
 471     icrypt_job j;
 472
 473     T( traceblk(TRACE_CRYPTO, "crypto: ciphertext reply:", buff, crp_size); )
 474
 475     icrypt_init(&j, sk, BLOWFISH_KEYSIZE, buff + crp_iv);
 476     icrypt_decrypt(&j, buff + crp_cipher,
 477                    buff + crp_cipher, crp_size - crp_cipher);
 478     burn(j);
 479
 480     T( traceblk(TRACE_CRYPTO, "crypto: plaintext reply:", buff, crp_size); )
 481   }
 482
 483   {
 484     /* --- Check validity --- */
 485
 486     md5 md;
 487     unsigned char mdbuf[MD5_HASHSIZE];
 488     char b[8];
 489
 490     /* --- Check the checksum --- */
 491
 492     md5_init(&md);
 493     md5_buffer(&md, buff + crp_cipher, crp_check - crp_cipher);
 494     md5_final(&md, mdbuf);
 495     if (memcmp(buff + crp_check, mdbuf, 4) != 0) {
 496       syslog(LOG_INFO, "reply rejected: bad checksum");
 497       T( trace(TRACE_CRYPTO, "crypto: bad checksum on reply"); )
 498       return (-1);
 499     }
 500
 501     /* --- Check the identifier --- */
 502
 503     store32(b + 0, t); store32(b + 4, pid);
 504     if (memcmp(b, buff + crp_time, sizeof(b)) != 0) {
 505       syslog(LOG_INFO, "reply rejected: bad identification marker");
 506       T( trace(TRACE_CRYPTO, "crypto: bad id on reply"); )
 507       return (-1);
 508     }
 509   }
 510
 511   /* --- Return the value --- */
 512
 513   T( trace(TRACE_CRYPTO, "crypto: valid reply received"); )
 514   return (buff[crp_answer]);
 515 }
 516
 517 /*----- Test rig ----------------------------------------------------------*/
 518
 519 #ifdef TEST_RIG
 520
 521 int main(int argc, char *argv[])
 522 {
 523   unsigned char buff[8];
 524   unsigned char sk[BLOWFISH_KEYSIZE], k[BLOWFISH_KEYSIZE];
 525   FILE *fp;
 526
 527   ego(argv[0]);
 528   traceon(stdout, TRACE_CRYPTO);
 529   if (argc < 3)
 530     die("bad args");
 531   fp = fopen(argv[1], "r");
 532   if (!fp)
 533     die("fopen: %s", strerror(errno));
 534   tx_getBits(k, 128, fp);
 535   fclose(fp);
 536   crypt__sessionKey(argv[2], k, sk, buff);
 537   return (0);
 538 }
 539
 540 #endif
 541
 542 /*----- That's all, folks -------------------------------------------------*/