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keyexch: Simplify key-exchange protocol.
[tripe] / keyexch.c
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1/* -*-c-*-
2 *
3 * $Id$
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/*----- Header files ------------------------------------------------------*/
30
31#include "tripe.h"
32
33/*----- Brief protocol overview -------------------------------------------*
34 *
35 * Let %$G$% be a cyclic group; let %$g$% be a generator of %$G$%, and let
36 * %$q$% be the order of %$G$%; for a key %$K$%, let %$E_K(\cdot)$% denote
37 * application of the symmetric packet protocol to a message; let
38 * %$H(\cdot)$% be the random oracle. Let $\alpha \inr \{0,\ldots,q - 1\}$%
39 * be Alice's private key; let %$a = g^\alpha$% be her public key; let %$b$%
40 * be Bob's public key.
41 *
42 * At the beginning of the session, Alice chooses
43 *
44 * %$\rho_A \inr \{0, \ldots q - 1\}$%
45 *
46 * We also have:
47 *
48 * %$r_A = g^{\rho_A}$% Alice's challenge
49 * %$c_A = H(\cookie{cookie}, r_A)$% Alice's cookie
50 * %$v_A = \rho_A \xor H(\cookie{expected-reply}, a, r_A, r_B, b^{\rho_A})$%
51 * Alice's challenge check value
52 * %$r_B^\alpha = a^{\rho_B}$% Alice's reply
53 * %$K = r_B^{\rho_A} = r_B^{\rho_A} = g^{\rho_A\rho_B}$%
54 * Alice and Bob's shared secret key
55 * %$w_A = H(\cookie{switch-request}, c_A, c_B)$%
56 * Alice's switch request value
57 * %$u_A = H(\cookie{switch-confirm}, c_A, c_B)$%
58 * Alice's switch confirm value
59 *
60 * The messages are then:
61 *
62 * %$\cookie{kx-pre-challenge}, r_A$%
63 * Initial greeting. In state @KXS_CHAL@.
64 *
65 * %$\cookie{kx-challenge}, r_A, c_B, v_A$%
66 * Here's a full challenge for you to answer.
67 *
68 * %$\cookie{kx-reply}, R_A, c_B, v_A, E_K(r_B^\alpha))$%
69 * Challenge accpeted: here's the answer. Commit to my challenge. Move
70 * to @KXS_COMMIT@.
71 *
72 * %$\cookie{kx-switch-rq}, c_A, c_B, E_K(r_B^\alpha, w_A))$%
73 * Reply received: here's my reply. Committed; send data; move to
74 * @KXS_SWITCH@.
75 *
76 * %$\cookie{kx-switch-ok}, E_K(u_A))$%
77 * Switch received. Committed; send data; move to @KXS_SWITCH@.
78 */
79
80/*----- Tunable parameters ------------------------------------------------*/
81
82#define T_VALID MIN(2) /* Challenge validity period */
83#define T_RETRY SEC(10) /* Challenge retransmit interval */
84
85#define VALIDP(kx, now) ((now) < (kx)->t_valid)
86
87/*----- Static tables -----------------------------------------------------*/
88
89static const char *const pkname[] = {
90 "pre-challenge", "cookie", "challenge",
91 "reply", "switch-rq", "switch-ok"
92};
93
94/*----- Various utilities -------------------------------------------------*/
95
96/* --- @hashge@ --- *
97 *
98 * Arguments: @ghash *h@ = pointer to hash context
99 * @ge *x@ = pointer to group element
100 *
101 * Returns: ---
102 *
103 * Use: Adds the hash of a group element to the context. Corrupts
104 * @buf_t@.
105 */
106
107static void hashge(ghash *h, ge *x)
108{
109 buf b;
110 buf_init(&b, buf_t, sizeof(buf_t));
111 G_TOBUF(gg, &b, x);
112 assert(BOK(&b));
113 GH_HASH(h, BBASE(&b), BLEN(&b));
114}
115
116/* --- @mpmask@ --- *
117 *
118 * Arguments: @buf *b@ = output buffer
119 * @mp *x@ = the plaintext integer
120 * @size_t n@ = the expected size of the plaintext
121 * @const octet *k@ = pointer to key material
122 * @size_t ksz@ = size of the key
123 *
124 * Returns: Pointer to the output.
125 *
126 * Use: Masks a multiprecision integer: returns %$x \xor H(k)$%, so
127 * it's a random oracle thing rather than an encryption thing.
128 */
129
130static octet *mpmask(buf *b, mp *x, size_t n, const octet *k, size_t ksz)
131{
132 gcipher *mgf;
133 octet *p;
134
135 if ((p = buf_get(b, n)) == 0)
136 return (0);
137 mgf = GC_INIT(algs.mgf, k, ksz);
138 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
139 trace(T_CRYPTO, "masking index = %s", mpstr(x));
140 trace_block(T_CRYPTO, "masking key", k, ksz);
141 }))
142 mp_storeb(x, buf_t, n);
143 GC_ENCRYPT(mgf, buf_t, p, n);
144 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
145 trace_block(T_CRYPTO, "index plaintext", buf_t, n);
146 trace_block(T_CRYPTO, "masked ciphertext", p, n);
147 }))
148 GC_DESTROY(mgf);
149 return (p);
150}
151
152/* --- @mpunmask@ --- *
153 *
154 * Arguments: @mp *d@ = the output integer
155 * @const octet *p@ = pointer to the ciphertext
156 * @size_t n@ = the size of the ciphertext
157 * @const octet *k@ = pointer to key material
158 * @size_t ksz@ = size of the key
159 *
160 * Returns: The decrypted integer, or null.
161 *
162 * Use: Unmasks a multiprecision integer.
163 */
164
165static mp *mpunmask(mp *d, const octet *p, size_t n,
166 const octet *k, size_t ksz)
167{
168 gcipher *mgf;
169
170 mgf = GC_INIT(algs.mgf, k, ksz);
171 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
172 trace_block(T_CRYPTO, "unmasking key", k, ksz);
173 trace_block(T_CRYPTO, "masked ciphertext", p, n);
174 }))
175 GC_DECRYPT(mgf, p, buf_t, n);
176 d = mp_loadb(d, buf_t, n);
177 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
178 trace_block(T_CRYPTO, "index plaintext", buf_t, n);
179 trace(T_CRYPTO, "unmasked index = %s", mpstr(d));
180 }))
181 GC_DESTROY(mgf);
182 return (d);
183}
184
185/* --- @hashcheck@ --- *
186 *
187 * Arguments: @ge *kpub@ = sender's public key
188 * @ge *cc@ = receiver's challenge
189 * @ge *c@ = sender's challenge
190 * @ge *y@ = reply to sender's challenge
191 *
192 * Returns: Pointer to the hash value (in @buf_t@)
193 *
194 * Use: Computes the check-value hash, used to mask or unmask
195 * indices to prove the validity of challenges. This computes
196 * the masking key used in challenge check values. This is
197 * really the heart of the whole thing, since it ensures that
198 * the index can be recovered from the history of hashing
199 * queries, which gives us (a) a proof that the authentication
200 * process is zero-knowledge, and (b) a proof that the whole
201 * key-exchange is deniable.
202 */
203
204static const octet *hashcheck(ge *kpub, ge *cc, ge *c, ge *y)
205{
206 ghash *h = GH_INIT(algs.h);
207
208 HASH_STRING(h, "tripe-expected-reply");
209 hashge(h, kpub);
210 hashge(h, cc);
211 hashge(h, c);
212 hashge(h, y);
213 GH_DONE(h, buf_t);
214 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
215 trace(T_CRYPTO, "computing challenge check hash");
216 trace(T_CRYPTO, "public key = %s", gestr(gg, kpub));
217 trace(T_CRYPTO, "receiver challenge = %s", gestr(gg, cc));
218 trace(T_CRYPTO, "sender challenge = %s", gestr(gg, c));
219 trace(T_CRYPTO, "sender reply = %s", gestr(gg, y));
220 trace_block(T_CRYPTO, "hash output", buf_t, algs.hashsz);
221 }))
222 GH_DESTROY(h);
223 return (buf_t);
224}
225
226/* --- @sendchallenge@ --- *
227 *
228 * Arguments: @keyexch *kx@ = pointer to key exchange block
229 * @buf *b@ = output buffer for challenge
230 * @ge *c@ = peer's actual challenge
231 * @const octet *hc@ = peer's challenge cookie
232 *
233 * Returns: ---
234 *
235 * Use: Writes a full challenge to the message buffer.
236 */
237
238static void sendchallenge(keyexch *kx, buf *b, ge *c, const octet *hc)
239{
240 G_TOBUF(gg, b, kx->c);
241 buf_put(b, hc, algs.hashsz);
242 mpmask(b, kx->alpha, indexsz,
243 hashcheck(kpub, c, kx->c, kx->rx), algs.hashsz);
244}
245
246/* --- @timer@ --- *
247 *
248 * Arguments: @struct timeval *tv@ = the current time
249 * @void *v@ = pointer to key exchange context
250 *
251 * Returns: ---
252 *
253 * Use: Acts when the key exchange timer goes off.
254 */
255
256static void timer(struct timeval *tv, void *v)
257{
258 keyexch *kx = v;
259 kx->f &= ~KXF_TIMER;
260 T( trace(T_KEYEXCH, "keyexch: timer has popped"); )
261 kx_start(kx, 0);
262}
263
264/* --- @settimer@ --- *
265 *
266 * Arguments: @keyexch *kx@ = pointer to key exchange context
267 * @time_t t@ = when to set the timer for
268 *
269 * Returns: ---
270 *
271 * Use: Sets the timer for the next key exchange attempt.
272 */
273
274static void settimer(keyexch *kx, time_t t)
275{
276 struct timeval tv;
277 if (kx->f & KXF_TIMER)
278 sel_rmtimer(&kx->t);
279 tv.tv_sec = t;
280 tv.tv_usec = 0;
281 sel_addtimer(&sel, &kx->t, &tv, timer, kx);
282 kx->f |= KXF_TIMER;
283}
284
285/*----- Challenge management ----------------------------------------------*/
286
287/* --- Notes on challenge management --- *
288 *
289 * We may get multiple different replies to our key exchange; some will be
290 * correct, some inserted by attackers. Up until @KX_THRESH@, all challenges
291 * received will be added to the table and given a full response. After
292 * @KX_THRESH@ distinct challenges are received, we return only a `cookie':
293 * our existing challenge, followed by a hash of the sender's challenge. We
294 * do %%\emph{not}%% give a bare challenge a reply slot at this stage. All
295 * properly-formed cookies are assigned a table slot: if none is spare, a
296 * used slot is randomly selected and destroyed. A cookie always receives a
297 * full reply.
298 */
299
300/* --- @kxc_destroy@ --- *
301 *
302 * Arguments: @kxchal *kxc@ = pointer to the challenge block
303 *
304 * Returns: ---
305 *
306 * Use: Disposes of a challenge block.
307 */
308
309static void kxc_destroy(kxchal *kxc)
310{
311 if (kxc->f & KXF_TIMER)
312 sel_rmtimer(&kxc->t);
313 G_DESTROY(gg, kxc->c);
314 G_DESTROY(gg, kxc->r);
315 ks_drop(kxc->ks);
316 DESTROY(kxc);
317}
318
319/* --- @kxc_stoptimer@ --- *
320 *
321 * Arguments: @kxchal *kxc@ = pointer to the challenge block
322 *
323 * Returns: ---
324 *
325 * Use: Stops the challenge's retry timer from sending messages.
326 * Useful when the state machine is in the endgame of the
327 * exchange.
328 */
329
330static void kxc_stoptimer(kxchal *kxc)
331{
332 if (kxc->f & KXF_TIMER)
333 sel_rmtimer(&kxc->t);
334 kxc->f &= ~KXF_TIMER;
335}
336
337/* --- @kxc_new@ --- *
338 *
339 * Arguments: @keyexch *kx@ = pointer to key exchange block
340 *
341 * Returns: A pointer to the challenge block.
342 *
343 * Use: Returns a pointer to a new challenge block to fill in.
344 */
345
346static kxchal *kxc_new(keyexch *kx)
347{
348 kxchal *kxc;
349 unsigned i;
350
351 /* --- If we're over reply threshold, discard one at random --- */
352
353 if (kx->nr < KX_NCHAL)
354 i = kx->nr++;
355 else {
356 i = rand_global.ops->range(&rand_global, KX_NCHAL);
357 kxc_destroy(kx->r[i]);
358 }
359
360 /* --- Fill in the new structure --- */
361
362 kxc = CREATE(kxchal);
363 kxc->c = G_CREATE(gg);
364 kxc->r = G_CREATE(gg);
365 kxc->ks = 0;
366 kxc->kx = kx;
367 kxc->f = 0;
368 kx->r[i] = kxc;
369 return (kxc);
370}
371
372/* --- @kxc_bychal@ --- *
373 *
374 * Arguments: @keyexch *kx@ = pointer to key exchange block
375 * @ge *c@ = challenge from remote host
376 *
377 * Returns: Pointer to the challenge block, or null.
378 *
379 * Use: Finds a challenge block, given its challenge.
380 */
381
382static kxchal *kxc_bychal(keyexch *kx, ge *c)
383{
384 unsigned i;
385
386 for (i = 0; i < kx->nr; i++) {
387 if (G_EQ(gg, c, kx->r[i]->c))
388 return (kx->r[i]);
389 }
390 return (0);
391}
392
393/* --- @kxc_byhc@ --- *
394 *
395 * Arguments: @keyexch *kx@ = pointer to key exchange block
396 * @const octet *hc@ = challenge hash from remote host
397 *
398 * Returns: Pointer to the challenge block, or null.
399 *
400 * Use: Finds a challenge block, given a hash of its challenge.
401 */
402
403static kxchal *kxc_byhc(keyexch *kx, const octet *hc)
404{
405 unsigned i;
406
407 for (i = 0; i < kx->nr; i++) {
408 if (memcmp(hc, kx->r[i]->hc, algs.hashsz) == 0)
409 return (kx->r[i]);
410 }
411 return (0);
412}
413
414/* --- @kxc_answer@ --- *
415 *
416 * Arguments: @keyexch *kx@ = pointer to key exchange block
417 * @kxchal *kxc@ = pointer to challenge block
418 *
419 * Returns: ---
420 *
421 * Use: Sends a reply to the remote host, according to the data in
422 * this challenge block.
423 */
424
425static void kxc_answer(keyexch *kx, kxchal *kxc);
426
427static void kxc_timer(struct timeval *tv, void *v)
428{
429 kxchal *kxc = v;
430 kxc->f &= ~KXF_TIMER;
431 kxc_answer(kxc->kx, kxc);
432}
433
434static void kxc_answer(keyexch *kx, kxchal *kxc)
435{
436 stats *st = p_stats(kx->p);
437 buf *b = p_txstart(kx->p, MSG_KEYEXCH | KX_REPLY);
438 struct timeval tv;
439 buf bb;
440
441 /* --- Build the reply packet --- */
442
443 T( trace(T_KEYEXCH, "keyexch: sending reply to `%s'", p_name(kx->p)); )
444 sendchallenge(kx, b, kxc->c, kxc->hc);
445 buf_init(&bb, buf_i, sizeof(buf_i));
446 G_TORAW(gg, &bb, kxc->r);
447 buf_flip(&bb);
448 ks_encrypt(kxc->ks, MSG_KEYEXCH | KX_REPLY, &bb, b);
449
450 /* --- Update the statistics --- */
451
452 if (BOK(b)) {
453 st->n_kxout++;
454 st->sz_kxout += BLEN(b);
455 p_txend(kx->p);
456 }
457
458 /* --- Schedule another resend --- */
459
460 if (kxc->f & KXF_TIMER)
461 sel_rmtimer(&kxc->t);
462 gettimeofday(&tv, 0);
463 tv.tv_sec += T_RETRY;
464 sel_addtimer(&sel, &kxc->t, &tv, kxc_timer, kxc);
465 kxc->f |= KXF_TIMER;
466}
467
468/*----- Individual message handlers ---------------------------------------*/
469
470/* --- @doprechallenge@ --- *
471 *
472 * Arguments: @keyexch *kx@ = pointer to key exchange block
473 * @buf *b@ = buffer containing the packet
474 *
475 * Returns: Zero if OK, nonzero of the packet was rejected.
476 *
477 * Use: Processes a pre-challenge message.
478 */
479
480static int doprechallenge(keyexch *kx, buf *b)
481{
482 stats *st = p_stats(kx->p);
483 ge *c = G_CREATE(gg);
484 ghash *h;
485
486 /* --- Ensure that we're in a sensible state --- */
487
488 if (kx->s != KXS_CHAL) {
489 a_warn("KX", "?PEER", kx->p, "unexpected", "pre-challenge", A_END);
490 goto bad;
491 }
492
493 /* --- Unpack the packet --- */
494
495 if (G_FROMBUF(gg, b, c) || BLEFT(b))
496 goto bad;
497
498 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
499 trace(T_CRYPTO, "crypto: challenge = %s", gestr(gg, c));
500 }))
501
502 /* --- Send out a full challenge by return --- */
503
504 b = p_txstart(kx->p, MSG_KEYEXCH | KX_CHAL);
505 h = GH_INIT(algs.h);
506 HASH_STRING(h, "tripe-cookie");
507 hashge(h, c);
508 sendchallenge(kx, b, c, GH_DONE(h, 0));
509 GH_DESTROY(h);
510 st->n_kxout++;
511 st->sz_kxout += BLEN(b);
512 p_txend(kx->p);
513
514 /* --- Done --- */
515
516 G_DESTROY(gg, c);
517 return (0);
518
519bad:
520 if (c) G_DESTROY(gg, c);
521 return (-1);
522}
523
524/* --- @respond@ --- *
525 *
526 * Arguments: @keyexch *kx@ = pointer to key exchange block
527 * @unsigned msg@ = message code for this packet
528 * @buf *b@ = buffer containing the packet
529 *
530 * Returns: Key-exchange challenge block, or null.
531 *
532 * Use: Computes a response for the given challenge, entering it into
533 * a challenge block and so on.
534 */
535
536static kxchal *respond(keyexch *kx, unsigned msg, buf *b)
537{
538 ge *c = G_CREATE(gg);
539 ge *r = G_CREATE(gg);
540 ge *cc = G_CREATE(gg);
541 const octet *hc, *ck;
542 size_t x, y, z;
543 mp *cv = 0;
544 kxchal *kxc;
545 ghash *h = 0;
546 buf bb;
547 int ok;
548
549 /* --- Unpack the packet --- */
550
551 if (G_FROMBUF(gg, b, c) ||
552 (hc = buf_get(b, algs.hashsz)) == 0 ||
553 (ck = buf_get(b, indexsz)) == 0) {
554 a_warn("KX", "?PEER", kx->p, "invalid", "%s", pkname[msg], A_END);
555 goto bad;
556 }
557 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
558 trace(T_CRYPTO, "crypto: challenge = %s", gestr(gg, c));
559 trace_block(T_CRYPTO, "crypto: cookie", hc, algs.hashsz);
560 trace_block(T_CRYPTO, "crypto: check-value", ck, indexsz);
561 }))
562
563 /* --- Discard a packet with an invalid cookie --- */
564
565 if (hc && memcmp(hc, kx->hc, algs.hashsz) != 0) {
566 a_warn("KX", "?PEER", "incorrect", "cookie", A_END);
567 goto bad;
568 }
569
570 /* --- Recover the check value and verify it --- *
571 *
572 * To avoid recomputation on replays, we store a hash of the `right'
573 * value. The `correct' value is unique, so this is right.
574 *
575 * This will also find a challenge block and, if necessary, populate it.
576 */
577
578 if ((kxc = kxc_bychal(kx, c)) != 0) {
579 h = GH_INIT(algs.h);
580 HASH_STRING(h, "tripe-check-hash");
581 GH_HASH(h, ck, indexsz);
582 ok = !memcmp(kxc->ck, GH_DONE(h, 0), algs.hashsz);
583 GH_DESTROY(h);
584 if (!ok) goto badcheck;
585 } else {
586
587 /* --- Compute the reply, and check the magic --- */
588
589 G_EXP(gg, r, c, kpriv);
590 cv = mpunmask(MP_NEW, ck, indexsz,
591 hashcheck(kx->kpub, kx->c, c, r), algs.hashsz);
592 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
593 trace(T_CRYPTO, "crypto: computed reply = %s", gestr(gg, r));
594 trace(T_CRYPTO, "crypto: recovered log = %s", mpstr(cv));
595 }))
596 if (MP_CMP(cv, >, gg->r) ||
597 (G_EXP(gg, cc, gg->g, cv), !G_EQ(gg, c, cc)))
598 goto badcheck;
599
600 /* --- Fill in a new challenge block --- */
601
602 kxc = kxc_new(kx);
603 G_COPY(gg, kxc->c, c);
604 G_COPY(gg, kxc->r, r);
605
606 h = GH_INIT(algs.h);
607 HASH_STRING(h, "tripe-check-hash");
608 GH_HASH(h, ck, indexsz);
609 GH_DONE(h, kxc->hc);
610 GH_DESTROY(h);
611
612 h = GH_INIT(algs.h);
613 HASH_STRING(h, "tripe-cookie");
614 hashge(h, kxc->c);
615 GH_DONE(h, kxc->hc);
616 GH_DESTROY(h);
617
618 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
619 trace_block(T_CRYPTO, "crypto: computed cookie", kxc->hc, algs.hashsz);
620 }))
621
622 /* --- Work out the shared key --- */
623
624 G_EXP(gg, r, c, kx->alpha);
625 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
626 trace(T_CRYPTO, "crypto: shared secret = %s", gestr(gg, r));
627 }))
628
629 /* --- Compute the switch messages --- */
630
631 h = GH_INIT(algs.h); HASH_STRING(h, "tripe-switch-request");
632 hashge(h, kx->c); hashge(h, kxc->c);
633 GH_DONE(h, kxc->hswrq_out); GH_DESTROY(h);
634 h = GH_INIT(algs.h); HASH_STRING(h, "tripe-switch-confirm");
635 hashge(h, kx->c); hashge(h, kxc->c);
636 GH_DONE(h, kxc->hswok_out); GH_DESTROY(h);
637
638 h = GH_INIT(algs.h); HASH_STRING(h, "tripe-switch-request");
639 hashge(h, kxc->c); hashge(h, kx->c);
640 GH_DONE(h, kxc->hswrq_in); GH_DESTROY(h);
641 h = GH_INIT(algs.h); HASH_STRING(h, "tripe-switch-confirm");
642 hashge(h, kxc->c); hashge(h, kx->c);
643 GH_DONE(h, kxc->hswok_in); GH_DESTROY(h);
644
645 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
646 trace_block(T_CRYPTO, "crypto: outbound switch request",
647 kxc->hswrq_out, algs.hashsz);
648 trace_block(T_CRYPTO, "crypto: outbound switch confirm",
649 kxc->hswok_out, algs.hashsz);
650 trace_block(T_CRYPTO, "crypto: inbound switch request",
651 kxc->hswrq_in, algs.hashsz);
652 trace_block(T_CRYPTO, "crypto: inbound switch confirm",
653 kxc->hswok_in, algs.hashsz);
654 }))
655
656 /* --- Create a new symmetric keyset --- */
657
658 buf_init(&bb, buf_o, sizeof(buf_o));
659 G_TOBUF(gg, &bb, kx->c); x = BLEN(&bb);
660 G_TOBUF(gg, &bb, kxc->c); y = BLEN(&bb);
661 G_TOBUF(gg, &bb, r); z = BLEN(&bb);
662 assert(BOK(&bb));
663
664 kxc->ks = ks_gen(BBASE(&bb), x, y, z, kx->p);
665 }
666
667 G_DESTROY(gg, c);
668 G_DESTROY(gg, cc);
669 G_DESTROY(gg, r);
670 mp_drop(cv);
671 return (kxc);
672
673badcheck:
674 a_warn("KX", "?PEER", kx->p, "bad-expected-reply-log", A_END);
675 goto bad;
676bad:
677 G_DESTROY(gg, c);
678 G_DESTROY(gg, cc);
679 G_DESTROY(gg, r);
680 mp_drop(cv);
681 return (0);
682}
683
684/* --- @dochallenge@ --- *
685 *
686 * Arguments: @keyexch *kx@ = pointer to key exchange block
687 * @unsigned msg@ = message code for the packet
688 * @buf *b@ = buffer containing the packet
689 *
690 * Returns: Zero if OK, nonzero if the packet was rejected.
691 *
692 * Use: Processes a packet containing a challenge.
693 */
694
695static int dochallenge(keyexch *kx, buf *b)
696{
697 kxchal *kxc;
698
699 if (kx->s != KXS_CHAL) {
700 a_warn("KX", "?PEER", kx->p, "unexpected", "challenge", A_END);
701 goto bad;
702 }
703 if ((kxc = respond(kx, KX_CHAL, b)) == 0)
704 goto bad;
705 if (BLEFT(b)) {
706 a_warn("KX", "?PEER", kx->p, "invalid", "challenge", A_END);
707 goto bad;
708 }
709 kxc_answer(kx, kxc);
710 return (0);
711
712bad:
713 return (-1);
714}
715
716/* --- @resend@ --- *
717 *
718 * Arguments: @keyexch *kx@ = pointer to key exchange context
719 *
720 * Returns: ---
721 *
722 * Use: Sends the next message for a key exchange.
723 */
724
725static void resend(keyexch *kx)
726{
727 kxchal *kxc;
728 buf bb;
729 stats *st = p_stats(kx->p);
730 buf *b;
731
732 switch (kx->s) {
733 case KXS_CHAL:
734 T( trace(T_KEYEXCH, "keyexch: sending prechallenge to `%s'",
735 p_name(kx->p)); )
736 b = p_txstart(kx->p, MSG_KEYEXCH | KX_PRECHAL);
737 G_TOBUF(gg, b, kx->c);
738 break;
739 case KXS_COMMIT:
740 T( trace(T_KEYEXCH, "keyexch: sending switch request to `%s'",
741 p_name(kx->p)); )
742 kxc = kx->r[0];
743 b = p_txstart(kx->p, MSG_KEYEXCH | KX_SWITCH);
744 buf_put(b, kx->hc, algs.hashsz);
745 buf_put(b, kxc->hc, algs.hashsz);
746 buf_init(&bb, buf_i, sizeof(buf_i));
747 G_TORAW(gg, &bb, kxc->r);
748 buf_put(&bb, kxc->hswrq_out, algs.hashsz);
749 buf_flip(&bb);
750 ks_encrypt(kxc->ks, MSG_KEYEXCH | KX_SWITCH, &bb, b);
751 break;
752 case KXS_SWITCH:
753 T( trace(T_KEYEXCH, "keyexch: sending switch confirmation to `%s'",
754 p_name(kx->p)); )
755 kxc = kx->r[0];
756 b = p_txstart(kx->p, MSG_KEYEXCH | KX_SWITCHOK);
757 buf_init(&bb, buf_i, sizeof(buf_i));
758 buf_put(&bb, kxc->hswok_out, algs.hashsz);
759 buf_flip(&bb);
760 ks_encrypt(kxc->ks, MSG_KEYEXCH | KX_SWITCHOK, &bb, b);
761 break;
762 default:
763 abort();
764 }
765
766 if (BOK(b)) {
767 st->n_kxout++;
768 st->sz_kxout += BLEN(b);
769 p_txend(kx->p);
770 }
771
772 if (kx->s < KXS_SWITCH)
773 settimer(kx, time(0) + T_RETRY);
774}
775
776/* --- @decryptrest@ --- *
777 *
778 * Arguments: @keyexch *kx@ = pointer to key exchange context
779 * @kxchal *kxc@ = pointer to challenge block
780 * @unsigned msg@ = type of incoming message
781 * @buf *b@ = encrypted remainder of the packet
782 *
783 * Returns: Zero if OK, nonzero on some kind of error.
784 *
785 * Use: Decrypts the remainder of the packet, and points @b@ at the
786 * recovered plaintext.
787 */
788
789static int decryptrest(keyexch *kx, kxchal *kxc, unsigned msg, buf *b)
790{
791 buf bb;
792
793 buf_init(&bb, buf_o, sizeof(buf_o));
794 if (ks_decrypt(kxc->ks, MSG_KEYEXCH | msg, b, &bb)) {
795 a_warn("KX", "?PEER", kx->p, "decrypt-failed", "%s", pkname[msg], A_END);
796 return (-1);
797 }
798 buf_init(b, BBASE(&bb), BLEN(&bb));
799 return (0);
800}
801
802/* --- @checkresponse@ --- *
803 *
804 * Arguments: @keyexch *kx@ = pointer to key exchange context
805 * @unsigned msg@ = type of incoming message
806 * @buf *b@ = decrypted remainder of the packet
807 *
808 * Returns: Zero if OK, nonzero on some kind of error.
809 *
810 * Use: Checks a reply or switch packet, ensuring that its response
811 * is correct.
812 */
813
814static int checkresponse(keyexch *kx, unsigned msg, buf *b)
815{
816 ge *r = G_CREATE(gg);
817
818 if (G_FROMRAW(gg, b, r)) {
819 a_warn("KX", "?PEER", kx->p, "invalid", "%s", pkname[msg], A_END);
820 goto bad;
821 }
822 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
823 trace(T_CRYPTO, "crypto: reply = %s", gestr(gg, r));
824 }))
825 if (!G_EQ(gg, r, kx->rx)) {
826 a_warn("KX", "?PEER", kx->p, "incorrect", "response", A_END);
827 goto bad;
828 }
829
830 G_DESTROY(gg, r);
831 return (0);
832
833bad:
834 G_DESTROY(gg, r);
835 return (-1);
836}
837
838/* --- @commit@ --- *
839 *
840 * Arguments: @keyexch *kx@ = pointer to key exchange context
841 * @kxchal *kxc@ = pointer to challenge to commit to
842 *
843 * Returns: ---
844 *
845 * Use: Commits to a particular challenge as being the `right' one,
846 * since a reply has arrived for it.
847 */
848
849static void commit(keyexch *kx, kxchal *kxc)
850{
851 unsigned i;
852
853 for (i = 0; i < kx->nr; i++) {
854 if (kx->r[i] != kxc)
855 kxc_destroy(kx->r[i]);
856 }
857 kx->r[0] = kxc;
858 kx->nr = 1;
859 kxc_stoptimer(kxc);
860 ksl_link(kx->ks, kxc->ks);
861}
862
863/* --- @doreply@ --- *
864 *
865 * Arguments: @keyexch *kx@ = pointer to key exchange context
866 * @buf *b@ = buffer containing packet
867 *
868 * Returns: Zero if OK, nonzero if the packet was rejected.
869 *
870 * Use: Handles a reply packet. This doesn't handle the various
871 * switch packets: they're rather too different.
872 */
873
874static int doreply(keyexch *kx, buf *b)
875{
876 kxchal *kxc;
877
878 if (kx->s != KXS_CHAL && kx->s != KXS_COMMIT) {
879 a_warn("KX", "?PEER", kx->p, "unexpected", "reply", A_END);
880 goto bad;
881 }
882 if ((kxc = respond(kx, KX_REPLY, b)) == 0 ||
883 decryptrest(kx, kxc, KX_REPLY, b) ||
884 checkresponse(kx, KX_REPLY, b))
885 goto bad;
886 if (BLEFT(b)) {
887 a_warn("KX", "?PEER", kx->p, "invalid", "reply", A_END);
888 goto bad;
889 }
890 if (kx->s == KXS_CHAL) {
891 commit(kx, kxc);
892 kx->s = KXS_COMMIT;
893 }
894 resend(kx);
895 return (0);
896
897bad:
898 return (-1);
899}
900
901/* --- @kxfinish@ --- *
902 *
903 * Arguments: @keyexch *kx@ = pointer to key exchange block
904 *
905 * Returns: ---
906 *
907 * Use: Sets everything up following a successful key exchange.
908 */
909
910static void kxfinish(keyexch *kx)
911{
912 kxchal *kxc = kx->r[0];
913 ks_activate(kxc->ks);
914 settimer(kx, ks_tregen(kxc->ks));
915 kx->s = KXS_SWITCH;
916 a_notify("KXDONE", "?PEER", kx->p, A_END);
917 p_stats(kx->p)->t_kx = time(0);
918}
919
920/* --- @doswitch@ --- *
921 *
922 * Arguments: @keyexch *kx@ = pointer to key exchange block
923 * @buf *b@ = pointer to buffer containing packet
924 *
925 * Returns: Zero if OK, nonzero if the packet was rejected.
926 *
927 * Use: Handles a reply with a switch request bolted onto it.
928 */
929
930static int doswitch(keyexch *kx, buf *b)
931{
932 const octet *hc_in, *hc_out, *hswrq;
933 kxchal *kxc;
934
935 if ((hc_in = buf_get(b, algs.hashsz)) == 0 ||
936 (hc_out = buf_get(b, algs.hashsz)) == 0) {
937 a_warn("KX", "?PEER", kx->p, "invalid", "switch-rq", A_END);
938 goto bad;
939 }
940 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
941 trace_block(T_CRYPTO, "crypto: challenge", hc_in, algs.hashsz);
942 trace_block(T_CRYPTO, "crypto: cookie", hc_out, algs.hashsz);
943 }))
944 if ((kxc = kxc_byhc(kx, hc_in)) == 0 ||
945 memcmp(hc_out, kx->hc, algs.hashsz) != 0) {
946 a_warn("KX", "?PEER", kx->p, "incorrect", "switch-rq", A_END);
947 goto bad;
948 }
949 if (decryptrest(kx, kxc, KX_SWITCH, b) ||
950 checkresponse(kx, KX_SWITCH, b))
951 goto bad;
952 if ((hswrq = buf_get(b, algs.hashsz)) == 0 || BLEFT(b)) {
953 a_warn("KX", "?PEER", "invalid", "switch-rq", A_END);
954 goto bad;
955 }
956 IF_TRACING(T_KEYEXCH, {
957 trace_block(T_CRYPTO, "crypto: switch request hash", hswrq, algs.hashsz);
958 })
959 if (memcmp(hswrq, kxc->hswrq_in, algs.hashsz) != 0) {
960 a_warn("KX", "?PEER", kx->p, "incorrect", "switch-rq", A_END);
961 goto bad;
962 }
963 if (kx->s == KXS_CHAL)
964 commit(kx, kxc);
965 if (kx->s < KXS_SWITCH)
966 kxfinish(kx);
967 resend(kx);
968 return (0);
969
970bad:
971 return (-1);
972}
973
974/* --- @doswitchok@ --- *
975 *
976 * Arguments: @keyexch *kx@ = pointer to key exchange block
977 * @buf *b@ = pointer to buffer containing packet
978 *
979 * Returns: Zero if OK, nonzero if the packet was rejected.
980 *
981 * Use: Handles a reply with a switch request bolted onto it.
982 */
983
984static int doswitchok(keyexch *kx, buf *b)
985{
986 const octet *hswok;
987 kxchal *kxc;
988 buf bb;
989
990 if (kx->s < KXS_COMMIT) {
991 a_warn("KX", "?PEER", kx->p, "unexpected", "switch-ok", A_END);
992 goto bad;
993 }
994 kxc = kx->r[0];
995 buf_init(&bb, buf_o, sizeof(buf_o));
996 if (decryptrest(kx, kxc, KX_SWITCHOK, b))
997 goto bad;
998 if ((hswok = buf_get(b, algs.hashsz)) == 0 || BLEFT(b)) {
999 a_warn("KX", "?PEER", "invalid", "switch-ok", A_END);
1000 goto bad;
1001 }
1002 IF_TRACING(T_KEYEXCH, {
1003 trace_block(T_CRYPTO, "crypto: switch confirmation hash",
1004 hswok, algs.hashsz);
1005 })
1006 if (memcmp(hswok, kxc->hswok_in, algs.hashsz) != 0) {
1007 a_warn("KX", "?PEER", kx->p, "incorrect", "switch-ok", A_END);
1008 goto bad;
1009 }
1010 if (kx->s < KXS_SWITCH)
1011 kxfinish(kx);
1012 return (0);
1013
1014bad:
1015 return (-1);
1016}
1017
1018/*----- Main code ---------------------------------------------------------*/
1019
1020/* --- @stop@ --- *
1021 *
1022 * Arguments: @keyexch *kx@ = pointer to key exchange context
1023 *
1024 * Returns: ---
1025 *
1026 * Use: Stops a key exchange dead in its tracks. Throws away all of
1027 * the context information. The context is left in an
1028 * inconsistent state. The only functions which understand this
1029 * state are @kx_free@ and @kx_init@ (which cause it internally
1030 * it), and @start@ (which expects it to be the prevailing
1031 * state).
1032 */
1033
1034static void stop(keyexch *kx)
1035{
1036 unsigned i;
1037
1038 if (kx->f & KXF_DEAD)
1039 return;
1040
1041 if (kx->f & KXF_TIMER)
1042 sel_rmtimer(&kx->t);
1043 for (i = 0; i < kx->nr; i++)
1044 kxc_destroy(kx->r[i]);
1045 mp_drop(kx->alpha);
1046 G_DESTROY(gg, kx->c);
1047 G_DESTROY(gg, kx->rx);
1048 kx->t_valid = 0;
1049 kx->f |= KXF_DEAD;
1050 kx->f &= ~KXF_TIMER;
1051}
1052
1053/* --- @start@ --- *
1054 *
1055 * Arguments: @keyexch *kx@ = pointer to key exchange context
1056 * @time_t now@ = the current time
1057 *
1058 * Returns: ---
1059 *
1060 * Use: Starts a new key exchange with the peer. The context must be
1061 * in the bizarre state left by @stop@ or @kx_init@.
1062 */
1063
1064static void start(keyexch *kx, time_t now)
1065{
1066 ghash *h;
1067
1068 assert(kx->f & KXF_DEAD);
1069
1070 kx->f &= ~KXF_DEAD;
1071 kx->nr = 0;
1072 kx->alpha = mprand_range(MP_NEW, gg->r, &rand_global, 0);
1073 kx->c = G_CREATE(gg); G_EXP(gg, kx->c, gg->g, kx->alpha);
1074 kx->rx = G_CREATE(gg); G_EXP(gg, kx->rx, kx->kpub, kx->alpha);
1075 kx->s = KXS_CHAL;
1076 kx->t_valid = now + T_VALID;
1077
1078 h = GH_INIT(algs.h);
1079 HASH_STRING(h, "tripe-cookie");
1080 hashge(h, kx->c);
1081 GH_DONE(h, kx->hc);
1082 GH_DESTROY(h);
1083
1084 IF_TRACING(T_KEYEXCH, {
1085 trace(T_KEYEXCH, "keyexch: creating new challenge");
1086 IF_TRACING(T_CRYPTO, {
1087 trace(T_CRYPTO, "crypto: secret = %s", mpstr(kx->alpha));
1088 trace(T_CRYPTO, "crypto: challenge = %s", gestr(gg, kx->c));
1089 trace(T_CRYPTO, "crypto: expected response = %s", gestr(gg, kx->rx));
1090 trace_block(T_CRYPTO, "crypto: challenge cookie", kx->hc, algs.hashsz);
1091 })
1092 })
1093}
1094
1095/* --- @checkpub@ --- *
1096 *
1097 * Arguments: @keyexch *kx@ = pointer to key exchange context
1098 *
1099 * Returns: Zero if OK, nonzero if the peer's public key has expired.
1100 *
1101 * Use: Deactivates the key-exchange until the peer acquires a new
1102 * public key.
1103 */
1104
1105static int checkpub(keyexch *kx)
1106{
1107 time_t now;
1108 if (kx->f & KXF_DEAD)
1109 return (-1);
1110 now = time(0);
1111 if (KEY_EXPIRED(now, kx->texp_kpub)) {
1112 stop(kx);
1113 a_warn("KX", "?PEER", kx->p, "public-key-expired", A_END);
1114 G_COPY(gg, kx->kpub, gg->i);
1115 kx->f &= ~KXF_PUBKEY;
1116 return (-1);
1117 }
1118 return (0);
1119}
1120
1121/* --- @kx_start@ --- *
1122 *
1123 * Arguments: @keyexch *kx@ = pointer to key exchange context
1124 * @int forcep@ = nonzero to ignore the quiet timer
1125 *
1126 * Returns: ---
1127 *
1128 * Use: Stimulates a key exchange. If a key exchage is in progress,
1129 * a new challenge is sent (unless the quiet timer forbids
1130 * this); if no exchange is in progress, one is commenced.
1131 */
1132
1133void kx_start(keyexch *kx, int forcep)
1134{
1135 time_t now = time(0);
1136
1137 if (checkpub(kx))
1138 return;
1139 if (forcep || !VALIDP(kx, now)) {
1140 stop(kx);
1141 start(kx, now);
1142 a_notify("KXSTART", "?PEER", kx->p, A_END);
1143 }
1144 resend(kx);
1145}
1146
1147/* --- @kx_message@ --- *
1148 *
1149 * Arguments: @keyexch *kx@ = pointer to key exchange context
1150 * @unsigned msg@ = the message code
1151 * @buf *b@ = pointer to buffer containing the packet
1152 *
1153 * Returns: ---
1154 *
1155 * Use: Reads a packet containing key exchange messages and handles
1156 * it.
1157 */
1158
1159void kx_message(keyexch *kx, unsigned msg, buf *b)
1160{
1161 time_t now = time(0);
1162 stats *st = p_stats(kx->p);
1163 size_t sz = BSZ(b);
1164 int rc;
1165
1166 if (checkpub(kx))
1167 return;
1168
1169 if (!VALIDP(kx, now)) {
1170 stop(kx);
1171 start(kx, now);
1172 }
1173
1174 T( trace(T_KEYEXCH, "keyexch: processing %s packet from `%s'",
1175 msg < KX_NMSG ? pkname[msg] : "unknown", p_name(kx->p)); )
1176
1177 switch (msg) {
1178 case KX_PRECHAL:
1179 rc = doprechallenge(kx, b);
1180 break;
1181 case KX_CHAL:
1182 rc = dochallenge(kx, b);
1183 break;
1184 case KX_REPLY:
1185 rc = doreply(kx, b);
1186 break;
1187 case KX_SWITCH:
1188 rc = doswitch(kx, b);
1189 break;
1190 case KX_SWITCHOK:
1191 rc = doswitchok(kx, b);
1192 break;
1193 default:
1194 a_warn("KX", "?PEER", kx->p, "unknown-message", "0x%02x", msg, A_END);
1195 rc = -1;
1196 break;
1197 }
1198
1199 if (rc)
1200 st->n_reject++;
1201 else {
1202 st->n_kxin++;
1203 st->sz_kxin += sz;
1204 }
1205}
1206
1207/* --- @kx_free@ --- *
1208 *
1209 * Arguments: @keyexch *kx@ = pointer to key exchange context
1210 *
1211 * Returns: ---
1212 *
1213 * Use: Frees everything in a key exchange context.
1214 */
1215
1216void kx_free(keyexch *kx)
1217{
1218 stop(kx);
1219 G_DESTROY(gg, kx->kpub);
1220}
1221
1222/* --- @kx_newkeys@ --- *
1223 *
1224 * Arguments: @keyexch *kx@ = pointer to key exchange context
1225 *
1226 * Returns: ---
1227 *
1228 * Use: Informs the key exchange module that its keys may have
1229 * changed. If fetching the new keys fails, the peer will be
1230 * destroyed, we log messages and struggle along with the old
1231 * keys.
1232 */
1233
1234void kx_newkeys(keyexch *kx)
1235{
1236 if (km_getpubkey(p_name(kx->p), kx->kpub, &kx->texp_kpub))
1237 return;
1238 kx->f |= KXF_PUBKEY;
1239 if ((kx->f & KXF_DEAD) || kx->s != KXS_SWITCH) {
1240 T( trace(T_KEYEXCH, "keyexch: restarting key negotiation with `%s'",
1241 p_name(kx->p)); )
1242 stop(kx);
1243 start(kx, time(0));
1244 resend(kx);
1245 }
1246}
1247
1248/* --- @kx_init@ --- *
1249 *
1250 * Arguments: @keyexch *kx@ = pointer to key exchange context
1251 * @peer *p@ = pointer to peer context
1252 * @keyset **ks@ = pointer to keyset list
1253 *
1254 * Returns: Zero if OK, nonzero if it failed.
1255 *
1256 * Use: Initializes a key exchange module. The module currently
1257 * contains no keys, and will attempt to initiate a key
1258 * exchange.
1259 */
1260
1261int kx_init(keyexch *kx, peer *p, keyset **ks)
1262{
1263 kx->ks = ks;
1264 kx->p = p;
1265 kx->kpub = G_CREATE(gg);
1266 if (km_getpubkey(p_name(p), kx->kpub, &kx->texp_kpub)) {
1267 G_DESTROY(gg, kx->kpub);
1268 return (-1);
1269 }
1270 kx->f = KXF_DEAD | KXF_PUBKEY;
1271 start(kx, time(0));
1272 resend(kx);
1273 /* Don't notify here: the ADD message hasn't gone out yet. */
1274 return (0);
1275}
1276
1277/*----- That's all, folks -------------------------------------------------*/