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

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