mdw@git.distorted.org.uk Git - tripe/blob - keyexch.c

   1 /* -*-c-*-
   2  *
   3  * $Id: keyexch.c,v 1.3 2001/06/19 22:07:09 mdw Exp $
   4  *
   5  * Key exchange protocol
   6  *
   7  * (c) 2001 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Trivial IP Encryption (TrIPE).
  13  *
  14  * TrIPE 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  * TrIPE 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 TrIPE; 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: keyexch.c,v $
  32  * Revision 1.3  2001/06/19 22:07:09  mdw
  33  * Cosmetic fixes.
  34  *
  35  * Revision 1.2  2001/02/16 21:24:27  mdw
  36  * Rewrite for new key exchange protocol.
  37  *
  38  * Revision 1.1  2001/02/03 20:26:37  mdw
  39  * Initial checkin.
  40  *
  41  */
  42
  43 /*----- Header files ------------------------------------------------------*/
  44
  45 #include "tripe.h"
  46
  47 /*----- Tunable parameters ------------------------------------------------*/
  48
  49 #define T_VALID MIN(2)
  50 #define T_RETRY SEC(10)
  51
  52 #define ISVALID(kx, now) ((now) < (kx)->t_valid)
  53
  54 /*----- Various utilities -------------------------------------------------*/
  55
  56 /* --- @hashmp@ --- *
  57  *
  58  * Arguments:   @HASH_CTX *r@ = pointer to hash context
  59  *              @mp *m@ = pointer to multiprecision integer
  60  *
  61  * Returns:     ---
  62  *
  63  * Use:         Adds the hash of a multiprecision integer to the context.
  64  *              Corrupts @buf_t@.
  65  */
  66
  67 static void hashmp(HASH_CTX *r, mp *m)
  68 {
  69   buf b;
  70   buf_init(&b, buf_t, sizeof(buf_t));
  71   buf_putmp(&b, m);
  72   assert(BOK(&b));
  73   HASH(r, BBASE(&b), BLEN(&b));
  74 }
  75
  76 /* --- @timer@ --- *
  77  *
  78  * Arguments:   @struct timeval *tv@ = the current time
  79  *              @void *v@ = pointer to key exchange context
  80  *
  81  * Returns:     ---
  82  *
  83  * Use:         Acts when the key exchange timer goes off.
  84  */
  85
  86 static void timer(struct timeval *tv, void *v)
  87 {
  88   keyexch *kx = v;
  89   kx->f &= ~KXF_TIMER;
  90   T( trace(T_KEYEXCH, "keyexch: timer has popped"); )
  91   kx_start(kx);
  92 }
  93
  94 /* --- @settimer@ --- *
  95  *
  96  * Arguments:   @keyexch *kx@ = pointer to key exchange context
  97  *              @time_t t@ = when to set the timer for
  98  *
  99  * Returns:     ---
 100  *
 101  * Use:         Sets the timer for the next key exchange attempt.
 102  */
 103
 104 static void settimer(keyexch *kx, time_t t)
 105 {
 106   struct timeval tv;
 107   if (kx->f & KXF_TIMER)
 108     sel_rmtimer(&kx->t);
 109   tv.tv_sec = t;
 110   tv.tv_usec = 0;
 111   sel_addtimer(&sel, &kx->t, &tv, timer, kx);
 112   kx->f |= KXF_TIMER;
 113 }
 114
 115 /*----- Challenge management ----------------------------------------------*/
 116
 117 /* --- Notes on challenge management --- *
 118  *
 119  * We may get multiple different replies to our key exchange; some will be
 120  * correct, some inserted by attackers.  Up until @KX_THRESH@, all challenges
 121  * received will be added to the table and given a full response.  After
 122  * @KX_THRESH@ distinct challenges are received, we return only a `cookie':
 123  * our existing challenge, followed by a hash of the sender's challenge.  We
 124  * do %%\emph{not}%% give a bare challenge a reply slot at this stage.  All
 125  * properly-formed cookies are assigned a table slot: if none is spare, a
 126  * used slot is randomly selected and destroyed.  A cookie always receives a
 127  * full reply.
 128  */
 129
 130 /* --- @kxc_destroy@ --- *
 131  *
 132  * Arguments:   @kxchal *kxc@ = pointer to the challenge block
 133  *
 134  * Returns:     ---
 135  *
 136  * Use:         Disposes of a challenge block.
 137  */
 138
 139 static void kxc_destroy(kxchal *kxc)
 140 {
 141   if (kxc->f & KXF_TIMER)
 142     sel_rmtimer(&kxc->t);
 143   mp_drop(kxc->c);
 144   mp_drop(kxc->r);
 145   ks_drop(kxc->ks);
 146   DESTROY(kxc);
 147 }
 148
 149 /* --- @kxc_stoptimer@ --- *
 150  *
 151  * Arguments:   @kxchal *kxc@ = pointer to the challenge block
 152  *
 153  * Returns:     ---
 154  *
 155  * Use:         Stops the challenge's retry timer from sending messages.
 156  *              Useful when the state machine is in the endgame of the
 157  *              exchange.
 158  */
 159
 160 static void kxc_stoptimer(kxchal *kxc)
 161 {
 162   if (kxc->f & KXF_TIMER)
 163     sel_rmtimer(&kxc->t);
 164 }
 165
 166 /* --- @kxc_new@ --- *
 167  *
 168  * Arguments:   @keyexch *kx@ = pointer to key exchange block
 169  *
 170  * Returns:     A pointer to the challenge block.
 171  *
 172  * Use:         Returns a pointer to a new challenge block to fill in.
 173  */
 174
 175 static kxchal *kxc_new(keyexch *kx)
 176 {
 177   kxchal *kxc;
 178   unsigned i;
 179
 180   /* --- If we're over reply threshold, discard one at random --- */
 181
 182   if (kx->nr < KX_NCHAL)
 183     i = kx->nr++;
 184   else {
 185     i = rand_global.ops->range(&rand_global, KX_NCHAL);
 186     kxc_destroy(kx->r[i]);
 187   }
 188
 189   /* --- Fill in the new structure --- */
 190
 191   kxc = CREATE(kxchal);
 192   kxc->c = 0;
 193   kxc->r = 0;
 194   kxc->ks = 0;
 195   kxc->kx = kx;
 196   kxc->f = 0;
 197   kx->r[i] = kxc;
 198   return (kxc);
 199 }
 200
 201 /* --- @kxc_bychal@ --- *
 202  *
 203  * Arguments:   @keyexch *kx@ = pointer to key exchange block
 204  *              @mp *c@ = challenge from remote host
 205  *
 206  * Returns:     Pointer to the challenge block, or null.
 207  *
 208  * Use:         Finds a challenge block, given its challenge.
 209  */
 210
 211 static kxchal *kxc_bychal(keyexch *kx, mp *c)
 212 {
 213   unsigned i;
 214
 215   for (i = 0; i < kx->nr; i++) {
 216     if (MP_EQ(c, kx->r[i]->c))
 217       return (kx->r[i]);
 218   }
 219   return (0);
 220 }
 221
 222 /* --- @kxc_byhc@ --- *
 223  *
 224  * Arguments:   @keyexch *kx@ = pointer to key exchange block
 225  *              @const octet *hc@ = challenge hash from remote host
 226  *
 227  * Returns:     Pointer to the challenge block, or null.
 228  *
 229  * Use:         Finds a challenge block, given a hash of its challenge.
 230  */
 231
 232 static kxchal *kxc_byhc(keyexch *kx, const octet *hc)
 233 {
 234   unsigned i;
 235
 236   for (i = 0; i < kx->nr; i++) {
 237     if (memcmp(hc, kx->r[i]->hc, HASHSZ) == 0)
 238       return (kx->r[i]);
 239   }
 240   return (0);
 241 }
 242
 243 /* --- @kxc_answer@ --- *
 244  *
 245  * Arguments:   @keyexch *kx@ = pointer to key exchange block
 246  *              @kxchal *kxc@ = pointer to challenge block
 247  *
 248  * Returns:     ---
 249  *
 250  * Use:         Sends a reply to the remote host, according to the data in
 251  *              this challenge block.
 252  */
 253
 254 static void kxc_answer(keyexch *kx, kxchal *kxc);
 255
 256 static void kxc_timer(struct timeval *tv, void *v)
 257 {
 258   kxchal *kxc = v;
 259   kxc->f &= ~KXF_TIMER;
 260   kxc_answer(kxc->kx, kxc);
 261 }
 262
 263 static void kxc_answer(keyexch *kx, kxchal *kxc)
 264 {
 265   stats *st = p_stats(kx->p);
 266   buf *b = p_txstart(kx->p, MSG_KEYEXCH | (kxc->r ? KX_REPLY : KX_CHAL));
 267   struct timeval tv;
 268   buf bb;
 269
 270   /* --- Build the reply packet --- */
 271
 272   if (!kxc->r)
 273     buf_putmp(b, kx->c);
 274   else
 275     buf_put(b, kx->hc, HASHSZ);
 276   buf_put(b, kxc->hc, HASHSZ);
 277   buf_put(b, kxc->hrx, HASHSZ);
 278
 279   /* --- Maybe send an actual reply, if we have one --- */
 280
 281   if (!kxc->r) {
 282     T( trace(T_KEYEXCH, "keyexch: resending challenge to `%s'",
 283              p_name(kx->p)); )
 284   } else {
 285     T( trace(T_KEYEXCH, "keyexch: sending reply to `%s'", p_name(kx->p)); )
 286     buf_init(&bb, buf_i, sizeof(buf_i));
 287     buf_putmp(&bb, kxc->r);
 288     buf_flip(&bb);
 289     ks_encrypt(kxc->ks, &bb, b);
 290   }
 291
 292   /* --- Update the statistics --- */
 293
 294   if (BOK(b)) {
 295     st->n_kxout++;
 296     st->sz_kxout += BLEN(b);
 297     p_txend(kx->p);
 298   }
 299
 300   /* --- Schedule another resend --- */
 301
 302   if (kxc->f & KXF_TIMER)
 303     sel_rmtimer(&kxc->t);
 304   gettimeofday(&tv, 0);
 305   tv.tv_sec += T_RETRY;
 306   sel_addtimer(&sel, &kxc->t, &tv, kxc_timer, kxc);
 307   kxc->f |= KXF_TIMER;
 308 }
 309
 310 /*----- Individual message handlers ---------------------------------------*/
 311
 312 /* --- @getreply@ --- *
 313  *
 314  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 315  *              @mp *c@ = a challenge
 316  *              @const octet *hrx@ = the supplied expected-reply hash
 317  *
 318  * Returns:     A pointer to the reply, or null if the reply-hash was wrong.
 319  *
 320  * Use:         Computes replies to challenges.
 321  */
 322
 323 static mp *getreply(keyexch *kx, mp *c, const octet *hrx)
 324 {
 325   mp *r = mpmont_exp(&mg, MP_NEW, c, kpriv.x);
 326   HASH_CTX h;
 327   octet buf[HASHSZ];
 328
 329   HASH_INIT(&h);
 330   HASH_STRING(&h, "tripe-expected-reply");
 331   hashmp(&h, c);
 332   hashmp(&h, kx->c);
 333   hashmp(&h, r);
 334   HASH_DONE(&h, buf);
 335   IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
 336     trace(T_CRYPTO, "crypto: computed reply = %s", mpstr(r));
 337     trace_block(T_CRYPTO, "crypto: computed reply hash", buf, HASHSZ);
 338   }))
 339   if (memcmp(buf, hrx, HASHSZ) != 0) {
 340     a_warn("invalid expected-reply hash from `%s'", p_name(kx->p));
 341     mp_drop(r);
 342     return (0);
 343   }
 344   return (r);
 345 }
 346
 347 /* --- @dochallenge@ --- *
 348  *
 349  * Arguments:   @keyexch *kx@ = pointer to key exchange block
 350  *              @unsigned msg@ = message code for the packet
 351  *              @buf *b@ = buffer containing the packet
 352  *
 353  * Returns:     Zero if OK, nonzero if the packet was rejected.
 354  *
 355  * Use:         Processes a packet containing a challenge.
 356  */
 357
 358 static int dochallenge(keyexch *kx, unsigned msg, buf *b)
 359 {
 360   mp *c = 0;
 361   const octet *hc = 0, *hrx = 0;
 362   kxchal *kxc;
 363   HASH_CTX h;
 364
 365   /* --- Ensure that we're in a sensible state --- */
 366
 367   if (kx->s != KXS_CHAL) {
 368     a_warn("unexpected challenge from `%s'", p_name(kx->p));
 369     goto bad;
 370   }
 371
 372   /* --- Unpack the packet --- */
 373
 374   if ((c = buf_getmp(b)) == 0 ||
 375       (msg >= KX_COOKIE && (hc = buf_get(b, HASHSZ)) == 0) ||
 376       (msg >= KX_CHAL && (hrx = buf_get(b, HASHSZ)) == 0) ||
 377       BLEFT(b)) {
 378     a_warn("malformed packet from `%s'", p_name(kx->p));
 379     goto bad;
 380   }
 381
 382   IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
 383     trace(T_CRYPTO, "crypto: challenge = %s", mpstr(c));
 384     if (hc) trace_block(T_CRYPTO, "crypto: cookie", hc, HASHSZ);
 385     if (hrx) trace_block(T_CRYPTO, "crypto: response hash", hrx, HASHSZ);
 386   }))
 387
 388   /* --- First, handle a bare challenge --- *
 389    *
 390    * If the table is heavily loaded, just emit a cookie and return.
 391    */
 392
 393   if (!hc && kx->nr >= KX_THRESH) {
 394     T( trace(T_KEYEXCH, "keyexch: too many challenges -- sending cookie"); )
 395     b = p_txstart(kx->p, MSG_KEYEXCH | KX_COOKIE);
 396     buf_putmp(b, kx->c);
 397     HASH_INIT(&h);
 398     HASH_STRING(&h, "tripe-cookie");
 399     hashmp(&h, c);
 400     HASH_DONE(&h, buf_get(b, HASHSZ));
 401     p_txend(kx->p);
 402     goto tidy;
 403   }
 404
 405   /* --- Discard a packet with an invalid cookie --- */
 406
 407   if (hc && memcmp(hc, kx->hc, HASHSZ) != 0) {
 408     a_warn("incorrect cookie from `%s'", p_name(kx->p));
 409     goto bad;
 410   }
 411
 412   /* --- Find a challenge block for this packet --- *
 413    *
 414    * If there isn't one already, create a new one.
 415    */
 416
 417   if ((kxc = kxc_bychal(kx, c)) == 0) {
 418     size_t x, y, z;
 419     mp *r;
 420
 421     /* --- Be careful here --- *
 422      *
 423      * If this is a full challenge, and it's the first time I've seen it, I
 424      * want to be able to throw it away before committing a table entry to
 425      * it.
 426      */
 427
 428     if (!hrx)
 429       kxc = kxc_new(kx);
 430     else {
 431       if ((r = getreply(kx, c, hrx)) == 0)
 432         goto bad;
 433       kxc = kxc_new(kx);
 434       kxc->r = r;
 435     }
 436     kxc->c = mp_copy(c);
 437
 438     /* --- Work out the cookie for this challenge --- */
 439
 440     HASH_INIT(&h);
 441     HASH_STRING(&h, "tripe-cookie");
 442     hashmp(&h, kxc->c);
 443     HASH_DONE(&h, kxc->hc);
 444
 445     /* --- Compute the expected-reply hash --- */
 446
 447     HASH_INIT(&h);
 448     HASH_STRING(&h, "tripe-expected-reply");
 449     hashmp(&h, kx->c);
 450     hashmp(&h, kxc->c);
 451     hashmp(&h, kx->rx);
 452     HASH_DONE(&h, kxc->hrx);
 453
 454     /* --- Work out the shared key --- */
 455
 456     r = mpmont_exp(&mg, MP_NEW, c, kx->alpha);
 457
 458     /* --- Compute the switch messages --- */
 459
 460     HASH_INIT(&h); HASH_STRING(&h, "tripe-switch-request");
 461     hashmp(&h, kx->c); hashmp(&h, kxc->c);
 462     HASH_DONE(&h, kxc->hswrq_out);
 463     HASH_INIT(&h); HASH_STRING(&h, "tripe-switch-confirm");
 464     hashmp(&h, kx->c); hashmp(&h, kxc->c);
 465     HASH_DONE(&h, kxc->hswok_out);
 466
 467     HASH_INIT(&h); HASH_STRING(&h, "tripe-switch-request");
 468     hashmp(&h, kxc->c); hashmp(&h, kx->c);
 469     HASH_DONE(&h, kxc->hswrq_in);
 470     HASH_INIT(&h); HASH_STRING(&h, "tripe-switch-confirm");
 471     hashmp(&h, kxc->c); hashmp(&h, kx->c);
 472     HASH_DONE(&h, kxc->hswok_in);
 473
 474     IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
 475       trace_block(T_CRYPTO, "crypto: computed cookie", kxc->hc, HASHSZ);
 476       trace_block(T_CRYPTO, "crypto: my reply hash", kxc->hrx, HASHSZ);
 477       trace(T_CRYPTO, "crypto: shared secret = %s", mpstr(r));
 478       trace_block(T_CRYPTO, "crypto: outbound switch request",
 479                   kxc->hswrq_out, HASHSZ);
 480       trace_block(T_CRYPTO, "crypto: outbound switch confirm",
 481                   kxc->hswok_out, HASHSZ);
 482       trace_block(T_CRYPTO, "crypto: inbound switch request",
 483                   kxc->hswrq_in, HASHSZ);
 484       trace_block(T_CRYPTO, "crypto: inbound switch confirm",
 485                   kxc->hswok_in, HASHSZ);
 486     }))
 487
 488     /* --- Create a new symmetric keyset --- */
 489
 490     buf_init(b, buf_o, sizeof(buf_o));
 491     buf_putmp(b, kx->c); x = BLEN(b);
 492     buf_putmp(b, kxc->c); y = BLEN(b);
 493     buf_putmp(b, r); z = BLEN(b);
 494     assert(BOK(b));
 495
 496     kxc->ks = ks_gen(BBASE(b), x, y, z);
 497     mp_drop(r);
 498   }
 499
 500   /* --- Answer the challenge if we need to --- */
 501
 502   if (hrx && !kxc->r) {
 503     mp *r;
 504     if ((r = getreply(kx, c, hrx)) == 0)
 505       goto bad;
 506     kxc->r = r;
 507   }
 508
 509   kxc_answer(kx, kxc);
 510
 511   /* --- Tidy up and go home --- */
 512
 513 tidy:
 514   mp_drop(c);
 515   return (0);
 516
 517 bad:
 518   mp_drop(c);
 519   return (-1);
 520 }
 521
 522 /* --- @resend@ --- *
 523  *
 524  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 525  *
 526  * Returns:     ---
 527  *
 528  * Use:         Sends the next message for a key exchange.
 529  */
 530
 531 static void resend(keyexch *kx)
 532 {
 533   kxchal *kxc;
 534   buf bb;
 535   stats *st = p_stats(kx->p);
 536   buf *b;
 537
 538   switch (kx->s) {
 539     case KXS_CHAL:
 540       T( trace(T_KEYEXCH, "sending prechallenge to `%s'", p_name(kx->p)); )
 541       b = p_txstart(kx->p, MSG_KEYEXCH | KX_PRECHAL);
 542       buf_putmp(b, kx->c);
 543       break;
 544     case KXS_COMMIT:
 545       T( trace(T_KEYEXCH, "sending switch request to `%s'", p_name(kx->p)); )
 546       kxc = kx->r[0];
 547       b = p_txstart(kx->p, MSG_KEYEXCH | KX_SWITCH);
 548       buf_put(b, kx->hc, HASHSZ);
 549       buf_put(b, kxc->hc, HASHSZ);
 550       buf_init(&bb, buf_i, sizeof(buf_i));
 551       buf_putmp(&bb, kxc->r);
 552       buf_put(&bb, kxc->hswrq_out, HASHSZ);
 553       buf_flip(&bb);
 554       ks_encrypt(kxc->ks, &bb, b);
 555       break;
 556     case KXS_SWITCH:
 557       T( trace(T_KEYEXCH, "sending switch confirmation to `%s'",
 558                p_name(kx->p)); )
 559       kxc = kx->r[0];
 560       b = p_txstart(kx->p, MSG_KEYEXCH | KX_SWITCHOK);
 561       buf_init(&bb, buf_i, sizeof(buf_i));
 562       buf_put(&bb, kxc->hswok_out, HASHSZ);
 563       buf_flip(&bb);
 564       ks_encrypt(kxc->ks, &bb, b);
 565       break;
 566     default:
 567       abort();
 568   }
 569
 570   if (BOK(b)) {
 571     st->n_kxout++;
 572     st->sz_kxout += BLEN(b);
 573     p_txend(kx->p);
 574   }
 575
 576   if (kx->s < KXS_SWITCH)
 577     settimer(kx, time(0) + T_RETRY);
 578 }
 579
 580 /* --- @matchreply@ --- *
 581  *
 582  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 583  *              @const octet *hc_in@ = a hash of his challenge
 584  *              @const octet *hc_out@ = a hash of my challenge (cookie)
 585  *              @const octet *krx@ = his expected-reply hash (optional)
 586  *              @buf *b@ = encrypted remainder of the packet
 587  *
 588  * Returns:     A pointer to the challenge block if OK, or null on failure.
 589  *
 590  * Use:         Checks a reply or switch packet, ensuring that its contents
 591  *              are sensible and correct.  If they are, @*b@ is set to point
 592  *              to the remainder of the encrypted data, and the correct
 593  *              challenge is returned.
 594  */
 595
 596 static kxchal *matchreply(keyexch *kx, const octet *hc_in,
 597                           const octet *hc_out, const octet *hrx, buf *b)
 598 {
 599   kxchal *kxc;
 600   buf bb;
 601   mp *r = 0;
 602
 603   /* --- Check the plaintext portions of the data --- */
 604
 605   IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
 606     trace_block(T_CRYPTO, "crypto: challenge", hc_in, HASHSZ);
 607     trace_block(T_CRYPTO, "crypto: cookie", hc_out, HASHSZ);
 608     if (hrx) trace_block(T_CRYPTO, "crypto: response hash", hrx, HASHSZ);
 609   }))
 610   if (memcmp(hc_out, kx->hc, HASHSZ) != 0) {
 611     a_warn("incorrect cookie from `%s'", p_name(kx->p));
 612     goto bad;
 613   }
 614   if ((kxc = kxc_byhc(kx, hc_in)) == 0) {
 615     a_warn("received reply for unknown challenge from `%s'", p_name(kx->p));
 616     goto bad;
 617   }
 618
 619   /* --- Maybe compute a reply for the challenge --- */
 620
 621   if (!kxc->r) {
 622     if (!hrx) {
 623       a_warn("unexpected switch request from `%s'", p_name(kx->p));
 624       goto bad;
 625     }
 626     if ((r = getreply(kx, kxc->c, hrx)) == 0)
 627       goto bad;
 628     kxc->r = r;
 629     r = 0;
 630   }
 631
 632   /* --- Decrypt the rest of the packet --- */
 633
 634   buf_init(&bb, buf_o, sizeof(buf_o));
 635   if (ks_decrypt(kxc->ks, b, &bb)) {
 636     a_warn("failed to decrypt reply from `%s'", p_name(kx->p));
 637     goto bad;
 638   }
 639   buf_init(b, BBASE(&bb), BLEN(&bb));
 640   if ((r = buf_getmp(b)) == 0) {
 641     a_warn("invalid reply packet from `%s'", p_name(kx->p));
 642     goto bad;
 643   }
 644   IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
 645     trace(T_CRYPTO, "crypto: reply = %s", mpstr(r));
 646   }))
 647   if (!mp_eq(r, kx->rx)) {
 648     a_warn("incorrect reply from `%s'", p_name(kx->p));
 649     goto bad;
 650   }
 651
 652   /* --- Done --- */
 653
 654   mp_drop(r);
 655   return (kxc);
 656
 657 bad:
 658   mp_drop(r);
 659   return (0);
 660 }
 661
 662 /* --- @commit@ --- *
 663  *
 664  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 665  *              @kxchal *kxc@ = pointer to challenge to commit to
 666  *
 667  * Returns:     ---
 668  *
 669  * Use:         Commits to a particular challenge as being the `right' one,
 670  *              since a reply has arrived for it.
 671  */
 672
 673 static void commit(keyexch *kx, kxchal *kxc)
 674 {
 675   unsigned i;
 676
 677   for (i = 0; i < kx->nr; i++) {
 678     if (kx->r[i] != kxc)
 679       kxc_destroy(kx->r[i]);
 680   }
 681   kx->r[0] = kxc;
 682   kx->nr = 1;
 683   kxc_stoptimer(kxc);
 684   ksl_link(kx->ks, kxc->ks);
 685 }
 686
 687 /* --- @doreply@ --- *
 688  *
 689  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 690  *              @buf *b@ = buffer containing packet
 691  *
 692  * Returns:     Zero if OK, nonzero if the packet was rejected.
 693  *
 694  * Use:         Handles a reply packet.  This doesn't handle the various
 695  *              switch packets: they're rather too different.
 696  */
 697
 698 static int doreply(keyexch *kx, buf *b)
 699 {
 700   const octet *hc_in, *hc_out, *hrx;
 701   kxchal *kxc;
 702
 703   if (kx->s != KXS_CHAL && kx->s != KXS_COMMIT) {
 704     a_warn("unexpected reply from `%s'", p_name(kx->p));
 705     goto bad;
 706   }
 707   if ((hc_in = buf_get(b, HASHSZ)) == 0 ||
 708       (hc_out = buf_get(b, HASHSZ)) == 0 ||
 709       (hrx = buf_get(b, HASHSZ)) == 0) {
 710     a_warn("invalid reply packet from `%s'", p_name(kx->p));
 711     goto bad;
 712   }
 713   if ((kxc = matchreply(kx, hc_in, hc_out, hrx, b)) == 0)
 714     goto bad;
 715   if (BLEFT(b)) {
 716     a_warn("invalid reply packet from `%s'", p_name(kx->p));
 717     goto bad;
 718   }
 719   if (kx->s == KXS_CHAL) {
 720     commit(kx, kxc);
 721     kx->s = KXS_COMMIT;
 722   }
 723   resend(kx);
 724   return (0);
 725
 726 bad:
 727   return (-1);
 728 }
 729
 730 /* --- @doswitch@ --- *
 731  *
 732  * Arguments:   @keyexch *kx@ = pointer to key exchange block
 733  *              @buf *b@ = pointer to buffer containing packet
 734  *
 735  * Returns:     Zero if OK, nonzero if the packet was rejected.
 736  *
 737  * Use:         Handles a reply with a switch request bolted onto it.
 738  */
 739
 740 static int doswitch(keyexch *kx, buf *b)
 741 {
 742   const octet *hc_in, *hc_out, *hswrq;
 743   kxchal *kxc;
 744
 745   if ((hc_in = buf_get(b, HASHSZ)) == 0 ||
 746       (hc_out = buf_get(b, HASHSZ)) == 0) {
 747     a_warn("invalid switch request from `%s'", p_name(kx->p));
 748     goto bad;
 749   }
 750   if ((kxc = matchreply(kx, hc_in, hc_out, 0, b)) == 0)
 751     goto bad;
 752   if ((hswrq = buf_get(b, HASHSZ)) == 0 || BLEFT(b)) {
 753     a_warn("invalid switch request from `%s'", p_name(kx->p));
 754     goto bad;
 755   }
 756   IF_TRACING(T_KEYEXCH, {
 757     trace_block(T_CRYPTO, "crypto: switch request hash", hswrq, HASHSZ);
 758   })
 759   if (memcmp(hswrq, kxc->hswrq_in, HASHSZ) != 0) {
 760     a_warn("incorrect switch request hash from `%s'", p_name(kx->p));
 761     goto bad;
 762   }
 763   switch (kx->s) {
 764     case KXS_CHAL:
 765       commit(kx, kxc);
 766     case KXS_COMMIT:
 767       ks_activate(kxc->ks);
 768       settimer(kx, ks_tregen(kxc->ks));
 769       kx->s = KXS_SWITCH;
 770       break;
 771   }
 772   resend(kx);
 773   return (0);
 774
 775 bad:
 776   return (-1);
 777 }
 778
 779 /* --- @doswitchok@ --- *
 780  *
 781  * Arguments:   @keyexch *kx@ = pointer to key exchange block
 782  *              @buf *b@ = pointer to buffer containing packet
 783  *
 784  * Returns:     Zero if OK, nonzero if the packet was rejected.
 785  *
 786  * Use:         Handles a reply with a switch request bolted onto it.
 787  */
 788
 789 static int doswitchok(keyexch *kx, buf *b)
 790 {
 791   const octet *hswok;
 792   kxchal *kxc;
 793   buf bb;
 794
 795   if (kx->s < KXS_COMMIT) {
 796     a_warn("unexpected switch confirmation from `%s'", p_name(kx->p));
 797     goto bad;
 798   }
 799   kxc = kx->r[0];
 800   buf_init(&bb, buf_o, sizeof(buf_o));
 801   if (ks_decrypt(kxc->ks, b, &bb)) {
 802     a_warn("failed to decrypt switch confirmation from `%s'", p_name(kx->p));
 803     goto bad;
 804   }
 805   buf_init(b, BBASE(&bb), BLEN(&bb));
 806   if ((hswok = buf_get(b, HASHSZ)) == 0 || BLEFT(b)) {
 807     a_warn("invalid switch confirmation from `%s'", p_name(kx->p));
 808     goto bad;
 809   }
 810   IF_TRACING(T_KEYEXCH, {
 811     trace_block(T_CRYPTO, "crypto: switch confirmation hash", hswok, HASHSZ);
 812   })
 813   if (memcmp(hswok, kxc->hswok_in, HASHSZ) != 0) {
 814     a_warn("incorrect switch confirmation hash from `%s'", p_name(kx->p));
 815     goto bad;
 816   }
 817   if (kx->s < KXS_SWITCH) {
 818     ks_activate(kxc->ks);
 819     settimer(kx, ks_tregen(kxc->ks));
 820     kx->s = KXS_SWITCH;
 821   }
 822   return (0);
 823
 824 bad:
 825   return (-1);
 826 }
 827
 828 /*----- Main code ---------------------------------------------------------*/
 829
 830 /* --- @stop@ --- *
 831  *
 832  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 833  *
 834  * Returns:     ---
 835  *
 836  * Use:         Stops a key exchange dead in its tracks.  Throws away all of
 837  *              the context information.  The context is left in an
 838  *              inconsistent state.  The only functions which understand this
 839  *              state are @kx_free@ and @kx_init@ (which cause it internally
 840  *              it), and @start@ (which expects it to be the prevailing
 841  *              state).
 842  */
 843
 844 static void stop(keyexch *kx)
 845 {
 846   unsigned i;
 847
 848   if (kx->f & KXF_TIMER)
 849     sel_rmtimer(&kx->t);
 850   for (i = 0; i < kx->nr; i++)
 851     kxc_destroy(kx->r[i]);
 852   mp_drop(kx->alpha);
 853   mp_drop(kx->c);
 854   mp_drop(kx->rx);
 855 }
 856
 857 /* --- @start@ --- *
 858  *
 859  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 860  *              @time_t now@ = the current time
 861  *
 862  * Returns:     ---
 863  *
 864  * Use:         Starts a new key exchange with the peer.  The context must be
 865  *              in the bizarre state left by @stop@ or @kx_init@.
 866  */
 867
 868 static void start(keyexch *kx, time_t now)
 869 {
 870   HASH_CTX h;
 871
 872   kx->nr = 0;
 873   kx->f = 0;
 874   kx->alpha = mprand_range(MP_NEW, kpriv.dp.q, &rand_global, 0);
 875   kx->c = mpmont_exp(&mg, MP_NEW, kpriv.dp.g, kx->alpha);
 876   kx->rx = mpmont_exp(&mg, MP_NEW, kx->kpub.y, kx->alpha);
 877   kx->s = KXS_CHAL;
 878   kx->t_valid = now + T_VALID;
 879
 880   HASH_INIT(&h);
 881   HASH_STRING(&h, "tripe-cookie");
 882   hashmp(&h, kx->c);
 883   HASH_DONE(&h, kx->hc);
 884
 885   IF_TRACING(T_KEYEXCH, {
 886     trace(T_KEYEXCH, "keyexch: creating new challenge");
 887     IF_TRACING(T_CRYPTO, {
 888       trace(T_CRYPTO, "crypto: secret = %s", mpstr(kx->alpha));
 889       trace(T_CRYPTO, "crypto: challenge = %s", mpstr(kx->c));
 890       trace(T_CRYPTO, "crypto: expected response = %s", mpstr(kx->rx));
 891       trace_block(T_CRYPTO, "crypto: challenge cookie", kx->hc, HASHSZ);
 892     })
 893   })
 894 }
 895
 896 /* --- @kx_start@ --- *
 897  *
 898  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 899  *
 900  * Returns:     ---
 901  *
 902  * Use:         Stimulates a key exchange.  If a key exchage is in progress,
 903  *              a new challenge is sent (unless the quiet timer forbids
 904  *              this); if no exchange is in progress, one is commenced.
 905  */
 906
 907 void kx_start(keyexch *kx)
 908 {
 909   time_t now = time(0);
 910
 911   if (!ISVALID(kx, now)) {
 912     stop(kx);
 913     start(kx, now);
 914   }
 915   resend(kx);
 916 }
 917
 918 /* --- @kx_message@ --- *
 919  *
 920  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 921  *              @unsigned msg@ = the message code
 922  *              @buf *b@ = pointer to buffer containing the packet
 923  *
 924  * Returns:     ---
 925  *
 926  * Use:         Reads a packet containing key exchange messages and handles
 927  *              it.
 928  */
 929
 930 void kx_message(keyexch *kx, unsigned msg, buf *b)
 931 {
 932   time_t now = time(0);
 933   stats *st = p_stats(kx->p);
 934   size_t sz = BSZ(b);
 935   int rc;
 936
 937 #ifndef NTRACE
 938   static const char *const pkname[] = {
 939     "prechallenge", "cookie", "challenge",
 940     "reply", "switch request", "switch confirmation"
 941   };
 942 #endif
 943
 944   if (!ISVALID(kx, now)) {
 945     stop(kx);
 946     start(kx, now);
 947   }
 948
 949   T( trace(T_KEYEXCH, "keyexch: processing %s packet from `%s'",
 950            msg < KX_NMSG ? pkname[msg] : "unknown", p_name(kx->p)); )
 951
 952   switch (msg) {
 953     case KX_PRECHAL:
 954     case KX_COOKIE:
 955     case KX_CHAL:
 956       rc = dochallenge(kx, msg, b);
 957       break;
 958     case KX_REPLY:
 959       rc = doreply(kx, b);
 960       break;
 961     case KX_SWITCH:
 962       rc = doswitch(kx, b);
 963       break;
 964     case KX_SWITCHOK:
 965       rc = doswitchok(kx, b);
 966       break;
 967     default:
 968       a_warn("unexpected key exchange message type %u from `%p'",
 969              p_name(kx->p));
 970       rc = -1;
 971       break;
 972   }
 973
 974   if (rc)
 975     st->n_reject++;
 976   else {
 977     st->n_kxin++;
 978     st->sz_kxin += sz;
 979   }
 980 }
 981
 982 /* --- @kx_free@ --- *
 983  *
 984  * Arguments:   @keyexch *kx@ = pointer to key exchange context
 985  *
 986  * Returns:     ---
 987  *
 988  * Use:         Frees everything in a key exchange context.
 989  */
 990
 991 void kx_free(keyexch *kx)
 992 {
 993   stop(kx);
 994   dh_pubfree(&kx->kpub);
 995 }
 996
 997 /* --- @kx_newkeys@ --- *
 998  *
 999  * Arguments:   @keyexch *kx@ = pointer to key exchange context
1000  *
1001  * Returns:     ---
1002  *
1003  * Use:         Informs the key exchange module that its keys may have
1004  *              changed.  If fetching the new keys fails, the peer will be
1005  *              destroyed, we log messages and struggle along with the old
1006  *              keys.
1007  */
1008
1009 void kx_newkeys(keyexch *kx)
1010 {
1011   dh_pub dp;
1012
1013   if (km_getpubkey(p_name(kx->p), &dp))
1014     return;
1015   dh_pubfree(&kx->kpub);
1016   kx->kpub = dp;
1017   if (kx->s != KXS_SWITCH) {
1018     T( trace(T_KEYEXCH, "keyexch: restarting key negotiation with `%s'",
1019              p_name(kx->p)); )
1020     kx->t_valid = 0;
1021     kx_start(kx);
1022   }
1023 }
1024
1025 /* --- @kx_init@ --- *
1026  *
1027  * Arguments:   @keyexch *kx@ = pointer to key exchange context
1028  *              @peer *p@ = pointer to peer context
1029  *              @keyset **ks@ = pointer to keyset list
1030  *
1031  * Returns:     Zero if OK, nonzero if it failed.
1032  *
1033  * Use:         Initializes a key exchange module.  The module currently
1034  *              contains no keys, and will attempt to initiate a key
1035  *              exchange.
1036  */
1037
1038 int kx_init(keyexch *kx, peer *p, keyset **ks)
1039 {
1040   kx->ks = ks;
1041   kx->p = p;
1042   if (km_getpubkey(p_name(p), &kx->kpub))
1043     return (-1);
1044   start(kx, time(0));
1045   resend(kx);
1046   return (0);
1047 }
1048
1049 /*----- That's all, folks -------------------------------------------------*/