3 * Key exchange protocol
5 * (c) 2001 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Trivial IP Encryption (TrIPE).
12 * TrIPE is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License as published by
14 * the Free Software Foundation; either version 2 of the License, or
15 * (at your option) any later version.
17 * TrIPE is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU General Public License for more details.
22 * You should have received a copy of the GNU General Public License
23 * along with TrIPE; if not, write to the Free Software Foundation,
24 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
27 /*----- Header files ------------------------------------------------------*/
31 /*----- Brief protocol overview -------------------------------------------*
33 * Let %$G$% be a cyclic group; let %$g$% be a generator of %$G$%, and let
34 * %$q$% be the order of %$G$%; for a key %$K$%, let %$E_K(\cdot)$% denote
35 * application of the symmetric packet protocol to a message; let
36 * %$H(\cdot)$% be the random oracle. Let $\alpha \inr \{0,\ldots,q - 1\}$%
37 * be Alice's private key; let %$a = g^\alpha$% be her public key; let %$b$%
38 * be Bob's public key.
40 * At the beginning of the session, Alice chooses
42 * %$\rho_A \inr \{0, \ldots q - 1\}$%
46 * %$r_A = g^{\rho_A}$% Alice's challenge
47 * %$c_A = H(\cookie{cookie}, r_A)$% Alice's cookie
48 * %$v_A = \rho_A \xor H(\cookie{expected-reply}, a, r_A, r_B, b^{\rho_A})$%
49 * Alice's challenge check value
50 * %$r_B^\alpha = a^{\rho_B}$% Alice's reply
51 * %$K = r_B^{\rho_A} = r_B^{\rho_A} = g^{\rho_A\rho_B}$%
52 * Alice and Bob's shared secret key
53 * %$w_A = H(\cookie{switch-request}, c_A, c_B)$%
54 * Alice's switch request value
55 * %$u_A = H(\cookie{switch-confirm}, c_A, c_B)$%
56 * Alice's switch confirm value
58 * The messages are then:
60 * %$\cookie{kx-pre-challenge}, r_A$%
61 * Initial greeting. In state @KXS_CHAL@.
63 * %$\cookie{kx-challenge}, r_A, c_B, v_A$%
64 * Here's a full challenge for you to answer.
66 * %$\cookie{kx-reply}, r_A, c_B, v_A, E_K(r_B^\alpha))$%
67 * Challenge accpeted: here's the answer. Commit to my challenge. Move
70 * %$\cookie{kx-switch-rq}, c_A, c_B, E_K(r_B^\alpha, w_A))$%
71 * Reply received: here's my reply. Committed; send data; move to
74 * %$\cookie{kx-switch-ok}, E_K(u_A))$%
75 * Switch received. Committed; send data; move to @KXS_SWITCH@.
78 /*----- Static tables -----------------------------------------------------*/
80 static const char *const pkname[] = {
81 "pre-challenge", "challenge", "reply", "switch-rq", "switch-ok"
84 /*----- Various utilities -------------------------------------------------*/
88 * Arguments: @const keyexch *kx@ = key exchange state
89 * @time_t now@ = current time in seconds
91 * Returns: Whether the challenge in the key-exchange state is still
92 * valid or should be regenerated.
95 #define VALIDP(kx, now) ((now) < (kx)->t_valid)
99 * Arguments: @ghash *h@ = pointer to hash context
100 * @ge *x@ = pointer to group element
104 * Use: Adds the hash of a group element to the context. Corrupts
108 static void hashge(ghash *h, ge *x)
111 buf_init(&b, buf_t, sizeof(buf_t));
114 GH_HASH(h, BBASE(&b), BLEN(&b));
117 /* --- @mpmask@ --- *
119 * Arguments: @buf *b@ = output buffer
120 * @mp *x@ = the plaintext integer
121 * @size_t n@ = the expected size of the plaintext
122 * @const octet *k@ = pointer to key material
123 * @size_t ksz@ = size of the key
125 * Returns: Pointer to the output.
127 * Use: Masks a multiprecision integer: returns %$x \xor H(k)$%, so
128 * it's a random oracle thing rather than an encryption thing.
131 static octet *mpmask(buf *b, mp *x, size_t n, const octet *k, size_t ksz)
136 if ((p = buf_get(b, n)) == 0)
138 mgf = GC_INIT(algs.mgf, k, ksz);
139 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
140 trace(T_CRYPTO, "masking index = %s", mpstr(x));
141 trace_block(T_CRYPTO, "masking key", k, ksz);
143 mp_storeb(x, buf_t, n);
144 GC_ENCRYPT(mgf, buf_t, p, n);
145 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
146 trace_block(T_CRYPTO, "index plaintext", buf_t, n);
147 trace_block(T_CRYPTO, "masked ciphertext", p, n);
153 /* --- @mpunmask@ --- *
155 * Arguments: @mp *d@ = the output integer
156 * @const octet *p@ = pointer to the ciphertext
157 * @size_t n@ = the size of the ciphertext
158 * @const octet *k@ = pointer to key material
159 * @size_t ksz@ = size of the key
161 * Returns: The decrypted integer, or null.
163 * Use: Unmasks a multiprecision integer.
166 static mp *mpunmask(mp *d, const octet *p, size_t n,
167 const octet *k, size_t ksz)
171 mgf = GC_INIT(algs.mgf, k, ksz);
172 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
173 trace_block(T_CRYPTO, "unmasking key", k, ksz);
174 trace_block(T_CRYPTO, "masked ciphertext", p, n);
176 GC_DECRYPT(mgf, p, buf_t, n);
177 d = mp_loadb(d, buf_t, n);
178 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
179 trace_block(T_CRYPTO, "index plaintext", buf_t, n);
180 trace(T_CRYPTO, "unmasked index = %s", mpstr(d));
186 /* --- @hashcheck@ --- *
188 * Arguments: @ge *kpub@ = sender's public key
189 * @ge *cc@ = receiver's challenge
190 * @ge *c@ = sender's challenge
191 * @ge *y@ = reply to sender's challenge
193 * Returns: Pointer to the hash value (in @buf_t@)
195 * Use: Computes the check-value hash, used to mask or unmask
196 * indices to prove the validity of challenges. This computes
197 * the masking key used in challenge check values. This is
198 * really the heart of the whole thing, since it ensures that
199 * the index can be recovered from the history of hashing
200 * queries, which gives us (a) a proof that the authentication
201 * process is zero-knowledge, and (b) a proof that the whole
202 * key-exchange is deniable.
205 static const octet *hashcheck(ge *kpub, ge *cc, ge *c, ge *y)
207 ghash *h = GH_INIT(algs.h);
209 HASH_STRING(h, "tripe-expected-reply");
215 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
216 trace(T_CRYPTO, "computing challenge check hash");
217 trace(T_CRYPTO, "public key = %s", gestr(gg, kpub));
218 trace(T_CRYPTO, "receiver challenge = %s", gestr(gg, cc));
219 trace(T_CRYPTO, "sender challenge = %s", gestr(gg, c));
220 trace(T_CRYPTO, "sender reply = %s", gestr(gg, y));
221 trace_block(T_CRYPTO, "hash output", buf_t, algs.hashsz);
227 /* --- @sendchallenge@ --- *
229 * Arguments: @keyexch *kx@ = pointer to key exchange block
230 * @buf *b@ = output buffer for challenge
231 * @ge *c@ = peer's actual challenge
232 * @const octet *hc@ = peer's challenge cookie
236 * Use: Writes a full challenge to the message buffer.
239 static void sendchallenge(keyexch *kx, buf *b, ge *c, const octet *hc)
241 G_TOBUF(gg, b, kx->c);
242 buf_put(b, hc, algs.hashsz);
243 mpmask(b, kx->alpha, indexsz,
244 hashcheck(kpub, c, kx->c, kx->rx), algs.hashsz);
249 * Arguments: @struct timeval *tv@ = the current time
250 * @void *v@ = pointer to key exchange context
254 * Use: Acts when the key exchange timer goes off.
257 static void timer(struct timeval *tv, void *v)
261 T( trace(T_KEYEXCH, "keyexch: timer has popped"); )
265 /* --- @settimer@ --- *
267 * Arguments: @keyexch *kx@ = pointer to key exchange context
268 * @struct timeval *tv@ = when to set the timer for
272 * Use: Sets the timer for the next key exchange attempt.
275 static void settimer(keyexch *kx, struct timeval *tv)
277 if (kx->f & KXF_TIMER) sel_rmtimer(&kx->t);
278 sel_addtimer(&sel, &kx->t, tv, timer, kx);
284 * Arguments: @struct timeval *tv@ = where to write the timeval
285 * @double t@ = a time as a floating point number
289 * Use: Converts a floating-point time into a timeval.
292 static void f2tv(struct timeval *tv, double t)
295 tv->tv_usec = (t - tv->tv_sec)*MILLION;
298 /* --- @wobble@ --- *
300 * Arguments: @double t@ = a time interval
302 * Returns: The same time interval, with a random error applied.
305 static double wobble(double t)
307 uint32 r = rand_global.ops->word(&rand_global);
308 double w = (r/F_2P32) - 0.5;
309 return (t + t*w*T_WOBBLE);
312 /* --- @rs_time@ --- *
314 * Arguments: @retry *rs@ = current retry state
315 * @struct timeval *tv@ = where to write the result
316 * @const struct timeval *now@ = current time, or null
320 * Use: Computes a time at which to retry sending a key-exchange
321 * packet. This algorithm is subject to change, but it's
322 * currently a capped exponential backoff, slightly randomized
323 * to try to keep clients from hammering a server that's only
326 * If @now@ is null then the function works out the time for
330 static void rs_time(retry *rs, struct timeval *tv, const struct timeval *now)
339 if (t > MIN(5)) t = MIN(5);
347 f2tv(&rtv, wobble(t));
348 TV_ADD(tv, now, &rtv);
351 /* --- @retry_reset@ --- *
353 * Arguments: @retry *rs@ = retry state
357 * Use: Resets a retry state to indicate that progress has been
358 * made. Also useful for initializing the state in the first
362 static void rs_reset(retry *rs) { rs->t = 0; }
364 /*----- Challenge management ----------------------------------------------*/
366 /* --- Notes on challenge management --- *
368 * We may get multiple different replies to our key exchange; some will be
369 * correct, some inserted by attackers. Up until @KX_THRESH@, all challenges
370 * received will be added to the table and given a full response. After
371 * @KX_THRESH@ distinct challenges are received, we return only a `cookie':
372 * our existing challenge, followed by a hash of the sender's challenge. We
373 * do %%\emph{not}%% give a bare challenge a reply slot at this stage. All
374 * properly-formed cookies are assigned a table slot: if none is spare, a
375 * used slot is randomly selected and destroyed. A cookie always receives a
379 /* --- @kxc_destroy@ --- *
381 * Arguments: @kxchal *kxc@ = pointer to the challenge block
385 * Use: Disposes of a challenge block.
388 static void kxc_destroy(kxchal *kxc)
390 if (kxc->f & KXF_TIMER)
391 sel_rmtimer(&kxc->t);
392 G_DESTROY(gg, kxc->c);
393 G_DESTROY(gg, kxc->r);
398 /* --- @kxc_stoptimer@ --- *
400 * Arguments: @kxchal *kxc@ = pointer to the challenge block
404 * Use: Stops the challenge's retry timer from sending messages.
405 * Useful when the state machine is in the endgame of the
409 static void kxc_stoptimer(kxchal *kxc)
411 if (kxc->f & KXF_TIMER)
412 sel_rmtimer(&kxc->t);
413 kxc->f &= ~KXF_TIMER;
416 /* --- @kxc_new@ --- *
418 * Arguments: @keyexch *kx@ = pointer to key exchange block
420 * Returns: A pointer to the challenge block.
422 * Use: Returns a pointer to a new challenge block to fill in.
425 static kxchal *kxc_new(keyexch *kx)
430 /* --- If we're over reply threshold, discard one at random --- */
432 if (kx->nr < KX_NCHAL)
435 i = rand_global.ops->range(&rand_global, KX_NCHAL);
436 kxc_destroy(kx->r[i]);
439 /* --- Fill in the new structure --- */
441 kxc = CREATE(kxchal);
442 kxc->c = G_CREATE(gg);
443 kxc->r = G_CREATE(gg);
452 /* --- @kxc_bychal@ --- *
454 * Arguments: @keyexch *kx@ = pointer to key exchange block
455 * @ge *c@ = challenge from remote host
457 * Returns: Pointer to the challenge block, or null.
459 * Use: Finds a challenge block, given its challenge.
462 static kxchal *kxc_bychal(keyexch *kx, ge *c)
466 for (i = 0; i < kx->nr; i++) {
467 if (G_EQ(gg, c, kx->r[i]->c))
473 /* --- @kxc_byhc@ --- *
475 * Arguments: @keyexch *kx@ = pointer to key exchange block
476 * @const octet *hc@ = challenge hash from remote host
478 * Returns: Pointer to the challenge block, or null.
480 * Use: Finds a challenge block, given a hash of its challenge.
483 static kxchal *kxc_byhc(keyexch *kx, const octet *hc)
487 for (i = 0; i < kx->nr; i++) {
488 if (memcmp(hc, kx->r[i]->hc, algs.hashsz) == 0)
494 /* --- @kxc_answer@ --- *
496 * Arguments: @keyexch *kx@ = pointer to key exchange block
497 * @kxchal *kxc@ = pointer to challenge block
501 * Use: Sends a reply to the remote host, according to the data in
502 * this challenge block.
505 static void kxc_answer(keyexch *kx, kxchal *kxc);
507 static void kxc_timer(struct timeval *tv, void *v)
510 kxc->f &= ~KXF_TIMER;
511 kxc_answer(kxc->kx, kxc);
514 static void kxc_answer(keyexch *kx, kxchal *kxc)
516 stats *st = p_stats(kx->p);
517 buf *b = p_txstart(kx->p, MSG_KEYEXCH | KX_REPLY);
521 /* --- Build the reply packet --- */
523 T( trace(T_KEYEXCH, "keyexch: sending reply to `%s'", p_name(kx->p)); )
524 sendchallenge(kx, b, kxc->c, kxc->hc);
525 buf_init(&bb, buf_i, sizeof(buf_i));
526 G_TORAW(gg, &bb, kxc->r);
528 ks_encrypt(kxc->ks, MSG_KEYEXCH | KX_REPLY, &bb, b);
530 /* --- Update the statistics --- */
534 st->sz_kxout += BLEN(b);
538 /* --- Schedule another resend --- */
540 if (kxc->f & KXF_TIMER)
541 sel_rmtimer(&kxc->t);
542 gettimeofday(&tv, 0);
543 rs_time(&kxc->rs, &tv, &tv);
544 sel_addtimer(&sel, &kxc->t, &tv, kxc_timer, kxc);
548 /*----- Individual message handlers ---------------------------------------*/
550 /* --- @doprechallenge@ --- *
552 * Arguments: @keyexch *kx@ = pointer to key exchange block
553 * @buf *b@ = buffer containing the packet
555 * Returns: Zero if OK, nonzero of the packet was rejected.
557 * Use: Processes a pre-challenge message.
560 static int doprechallenge(keyexch *kx, buf *b)
562 stats *st = p_stats(kx->p);
563 ge *c = G_CREATE(gg);
566 /* --- Ensure that we're in a sensible state --- */
568 if (kx->s != KXS_CHAL) {
569 a_warn("KX", "?PEER", kx->p, "unexpected", "pre-challenge", A_END);
573 /* --- Unpack the packet --- */
575 if (G_FROMBUF(gg, b, c) || BLEFT(b))
578 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
579 trace(T_CRYPTO, "crypto: challenge = %s", gestr(gg, c));
582 /* --- Send out a full challenge by return --- */
584 b = p_txstart(kx->p, MSG_KEYEXCH | KX_CHAL);
586 HASH_STRING(h, "tripe-cookie");
588 sendchallenge(kx, b, c, GH_DONE(h, 0));
591 st->sz_kxout += BLEN(b);
600 if (c) G_DESTROY(gg, c);
604 /* --- @respond@ --- *
606 * Arguments: @keyexch *kx@ = pointer to key exchange block
607 * @unsigned msg@ = message code for this packet
608 * @buf *b@ = buffer containing the packet
610 * Returns: Key-exchange challenge block, or null.
612 * Use: Computes a response for the given challenge, entering it into
613 * a challenge block and so on.
616 static kxchal *respond(keyexch *kx, unsigned msg, buf *b)
618 ge *c = G_CREATE(gg);
619 ge *r = G_CREATE(gg);
620 ge *cc = G_CREATE(gg);
621 const octet *hc, *ck;
629 /* --- Unpack the packet --- */
631 if (G_FROMBUF(gg, b, c) ||
632 (hc = buf_get(b, algs.hashsz)) == 0 ||
633 (ck = buf_get(b, indexsz)) == 0) {
634 a_warn("KX", "?PEER", kx->p, "invalid", "%s", pkname[msg], A_END);
637 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
638 trace(T_CRYPTO, "crypto: challenge = %s", gestr(gg, c));
639 trace_block(T_CRYPTO, "crypto: cookie", hc, algs.hashsz);
640 trace_block(T_CRYPTO, "crypto: check-value", ck, indexsz);
643 /* --- Discard a packet with an invalid cookie --- */
645 if (hc && memcmp(hc, kx->hc, algs.hashsz) != 0) {
646 a_warn("KX", "?PEER", kx->p, "incorrect", "cookie", A_END);
650 /* --- Recover the check value and verify it --- *
652 * To avoid recomputation on replays, we store a hash of the `right'
653 * value. The `correct' value is unique, so this is right.
655 * This will also find a challenge block and, if necessary, populate it.
658 if ((kxc = kxc_bychal(kx, c)) != 0) {
660 HASH_STRING(h, "tripe-check-hash");
661 GH_HASH(h, ck, indexsz);
662 ok = !memcmp(kxc->ck, GH_DONE(h, 0), algs.hashsz);
664 if (!ok) goto badcheck;
667 /* --- Compute the reply, and check the magic --- */
669 G_EXP(gg, r, c, kpriv);
670 cv = mpunmask(MP_NEW, ck, indexsz,
671 hashcheck(kx->kpub, kx->c, c, r), algs.hashsz);
672 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
673 trace(T_CRYPTO, "crypto: computed reply = %s", gestr(gg, r));
674 trace(T_CRYPTO, "crypto: recovered log = %s", mpstr(cv));
676 if (MP_CMP(cv, >, gg->r) ||
677 (G_EXP(gg, cc, gg->g, cv), !G_EQ(gg, c, cc)))
680 /* --- Fill in a new challenge block --- */
683 G_COPY(gg, kxc->c, c);
684 G_COPY(gg, kxc->r, r);
687 HASH_STRING(h, "tripe-check-hash");
688 GH_HASH(h, ck, indexsz);
693 HASH_STRING(h, "tripe-cookie");
698 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
699 trace_block(T_CRYPTO, "crypto: computed cookie", kxc->hc, algs.hashsz);
702 /* --- Work out the shared key --- */
704 G_EXP(gg, r, c, kx->alpha);
705 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
706 trace(T_CRYPTO, "crypto: shared secret = %s", gestr(gg, r));
709 /* --- Compute the switch messages --- */
711 h = GH_INIT(algs.h); HASH_STRING(h, "tripe-switch-request");
712 hashge(h, kx->c); hashge(h, kxc->c);
713 GH_DONE(h, kxc->hswrq_out); GH_DESTROY(h);
714 h = GH_INIT(algs.h); HASH_STRING(h, "tripe-switch-confirm");
715 hashge(h, kx->c); hashge(h, kxc->c);
716 GH_DONE(h, kxc->hswok_out); GH_DESTROY(h);
718 h = GH_INIT(algs.h); HASH_STRING(h, "tripe-switch-request");
719 hashge(h, kxc->c); hashge(h, kx->c);
720 GH_DONE(h, kxc->hswrq_in); GH_DESTROY(h);
721 h = GH_INIT(algs.h); HASH_STRING(h, "tripe-switch-confirm");
722 hashge(h, kxc->c); hashge(h, kx->c);
723 GH_DONE(h, kxc->hswok_in); GH_DESTROY(h);
725 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
726 trace_block(T_CRYPTO, "crypto: outbound switch request",
727 kxc->hswrq_out, algs.hashsz);
728 trace_block(T_CRYPTO, "crypto: outbound switch confirm",
729 kxc->hswok_out, algs.hashsz);
730 trace_block(T_CRYPTO, "crypto: inbound switch request",
731 kxc->hswrq_in, algs.hashsz);
732 trace_block(T_CRYPTO, "crypto: inbound switch confirm",
733 kxc->hswok_in, algs.hashsz);
736 /* --- Create a new symmetric keyset --- */
738 buf_init(&bb, buf_o, sizeof(buf_o));
739 G_TOBUF(gg, &bb, kx->c); x = BLEN(&bb);
740 G_TOBUF(gg, &bb, kxc->c); y = BLEN(&bb);
741 G_TOBUF(gg, &bb, r); z = BLEN(&bb);
744 kxc->ks = ks_gen(BBASE(&bb), x, y, z, kx->p);
754 a_warn("KX", "?PEER", kx->p, "bad-expected-reply-log", A_END);
764 /* --- @dochallenge@ --- *
766 * Arguments: @keyexch *kx@ = pointer to key exchange block
767 * @unsigned msg@ = message code for the packet
768 * @buf *b@ = buffer containing the packet
770 * Returns: Zero if OK, nonzero if the packet was rejected.
772 * Use: Processes a packet containing a challenge.
775 static int dochallenge(keyexch *kx, buf *b)
779 if (kx->s != KXS_CHAL) {
780 a_warn("KX", "?PEER", kx->p, "unexpected", "challenge", A_END);
783 if ((kxc = respond(kx, KX_CHAL, b)) == 0)
786 a_warn("KX", "?PEER", kx->p, "invalid", "challenge", A_END);
796 /* --- @resend@ --- *
798 * Arguments: @keyexch *kx@ = pointer to key exchange context
802 * Use: Sends the next message for a key exchange.
805 static void resend(keyexch *kx)
809 stats *st = p_stats(kx->p);
815 T( trace(T_KEYEXCH, "keyexch: sending prechallenge to `%s'",
817 b = p_txstart(kx->p, MSG_KEYEXCH | KX_PRECHAL);
818 G_TOBUF(gg, b, kx->c);
821 T( trace(T_KEYEXCH, "keyexch: sending switch request to `%s'",
824 b = p_txstart(kx->p, MSG_KEYEXCH | KX_SWITCH);
825 buf_put(b, kx->hc, algs.hashsz);
826 buf_put(b, kxc->hc, algs.hashsz);
827 buf_init(&bb, buf_i, sizeof(buf_i));
828 G_TORAW(gg, &bb, kxc->r);
829 buf_put(&bb, kxc->hswrq_out, algs.hashsz);
831 ks_encrypt(kxc->ks, MSG_KEYEXCH | KX_SWITCH, &bb, b);
834 T( trace(T_KEYEXCH, "keyexch: sending switch confirmation to `%s'",
837 b = p_txstart(kx->p, MSG_KEYEXCH | KX_SWITCHOK);
838 buf_init(&bb, buf_i, sizeof(buf_i));
839 buf_put(&bb, kxc->hswok_out, algs.hashsz);
841 ks_encrypt(kxc->ks, MSG_KEYEXCH | KX_SWITCHOK, &bb, b);
849 st->sz_kxout += BLEN(b);
853 if (kx->s < KXS_SWITCH) {
854 rs_time(&kx->rs, &tv, 0);
859 /* --- @decryptrest@ --- *
861 * Arguments: @keyexch *kx@ = pointer to key exchange context
862 * @kxchal *kxc@ = pointer to challenge block
863 * @unsigned msg@ = type of incoming message
864 * @buf *b@ = encrypted remainder of the packet
866 * Returns: Zero if OK, nonzero on some kind of error.
868 * Use: Decrypts the remainder of the packet, and points @b@ at the
869 * recovered plaintext.
872 static int decryptrest(keyexch *kx, kxchal *kxc, unsigned msg, buf *b)
876 buf_init(&bb, buf_o, sizeof(buf_o));
877 if (ks_decrypt(kxc->ks, MSG_KEYEXCH | msg, b, &bb)) {
878 a_warn("KX", "?PEER", kx->p, "decrypt-failed", "%s", pkname[msg], A_END);
881 if (!BOK(&bb)) return (-1);
882 buf_init(b, BBASE(&bb), BLEN(&bb));
886 /* --- @checkresponse@ --- *
888 * Arguments: @keyexch *kx@ = pointer to key exchange context
889 * @unsigned msg@ = type of incoming message
890 * @buf *b@ = decrypted remainder of the packet
892 * Returns: Zero if OK, nonzero on some kind of error.
894 * Use: Checks a reply or switch packet, ensuring that its response
898 static int checkresponse(keyexch *kx, unsigned msg, buf *b)
900 ge *r = G_CREATE(gg);
902 if (G_FROMRAW(gg, b, r)) {
903 a_warn("KX", "?PEER", kx->p, "invalid", "%s", pkname[msg], A_END);
906 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
907 trace(T_CRYPTO, "crypto: reply = %s", gestr(gg, r));
909 if (!G_EQ(gg, r, kx->rx)) {
910 a_warn("KX", "?PEER", kx->p, "incorrect", "response", A_END);
922 /* --- @commit@ --- *
924 * Arguments: @keyexch *kx@ = pointer to key exchange context
925 * @kxchal *kxc@ = pointer to challenge to commit to
929 * Use: Commits to a particular challenge as being the `right' one,
930 * since a reply has arrived for it.
933 static void commit(keyexch *kx, kxchal *kxc)
937 for (i = 0; i < kx->nr; i++) {
939 kxc_destroy(kx->r[i]);
944 ksl_link(kx->ks, kxc->ks);
947 /* --- @doreply@ --- *
949 * Arguments: @keyexch *kx@ = pointer to key exchange context
950 * @buf *b@ = buffer containing packet
952 * Returns: Zero if OK, nonzero if the packet was rejected.
954 * Use: Handles a reply packet. This doesn't handle the various
955 * switch packets: they're rather too different.
958 static int doreply(keyexch *kx, buf *b)
962 if (kx->s != KXS_CHAL && kx->s != KXS_COMMIT) {
963 a_warn("KX", "?PEER", kx->p, "unexpected", "reply", A_END);
966 if ((kxc = respond(kx, KX_REPLY, b)) == 0 ||
967 decryptrest(kx, kxc, KX_REPLY, b) ||
968 checkresponse(kx, KX_REPLY, b))
971 a_warn("KX", "?PEER", kx->p, "invalid", "reply", A_END);
974 if (kx->s == KXS_CHAL) {
985 /* --- @kxfinish@ --- *
987 * Arguments: @keyexch *kx@ = pointer to key exchange block
991 * Use: Sets everything up following a successful key exchange.
994 static void kxfinish(keyexch *kx)
996 kxchal *kxc = kx->r[0];
997 struct timeval now, tv;
999 ks_activate(kxc->ks);
1000 gettimeofday(&now, 0);
1001 f2tv(&tv, wobble(T_REGEN));
1002 TV_ADD(&tv, &now, &tv);
1005 a_notify("KXDONE", "?PEER", kx->p, A_END);
1006 p_stats(kx->p)->t_kx = time(0);
1009 /* --- @doswitch@ --- *
1011 * Arguments: @keyexch *kx@ = pointer to key exchange block
1012 * @buf *b@ = pointer to buffer containing packet
1014 * Returns: Zero if OK, nonzero if the packet was rejected.
1016 * Use: Handles a reply with a switch request bolted onto it.
1019 static int doswitch(keyexch *kx, buf *b)
1021 const octet *hc_in, *hc_out, *hswrq;
1024 if ((hc_in = buf_get(b, algs.hashsz)) == 0 ||
1025 (hc_out = buf_get(b, algs.hashsz)) == 0) {
1026 a_warn("KX", "?PEER", kx->p, "invalid", "switch-rq", A_END);
1029 IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, {
1030 trace_block(T_CRYPTO, "crypto: challenge", hc_in, algs.hashsz);
1031 trace_block(T_CRYPTO, "crypto: cookie", hc_out, algs.hashsz);
1033 if ((kxc = kxc_byhc(kx, hc_in)) == 0 ||
1034 memcmp(hc_out, kx->hc, algs.hashsz) != 0) {
1035 a_warn("KX", "?PEER", kx->p, "incorrect", "switch-rq", A_END);
1038 if (decryptrest(kx, kxc, KX_SWITCH, b) ||
1039 checkresponse(kx, KX_SWITCH, b))
1041 if ((hswrq = buf_get(b, algs.hashsz)) == 0 || BLEFT(b)) {
1042 a_warn("KX", "?PEER", kx->p, "invalid", "switch-rq", A_END);
1045 IF_TRACING(T_KEYEXCH, {
1046 trace_block(T_CRYPTO, "crypto: switch request hash", hswrq, algs.hashsz);
1048 if (memcmp(hswrq, kxc->hswrq_in, algs.hashsz) != 0) {
1049 a_warn("KX", "?PEER", kx->p, "incorrect", "switch-rq", A_END);
1052 if (kx->s == KXS_CHAL)
1054 if (kx->s < KXS_SWITCH)
1063 /* --- @doswitchok@ --- *
1065 * Arguments: @keyexch *kx@ = pointer to key exchange block
1066 * @buf *b@ = pointer to buffer containing packet
1068 * Returns: Zero if OK, nonzero if the packet was rejected.
1070 * Use: Handles a reply with a switch request bolted onto it.
1073 static int doswitchok(keyexch *kx, buf *b)
1079 if (kx->s < KXS_COMMIT) {
1080 a_warn("KX", "?PEER", kx->p, "unexpected", "switch-ok", A_END);
1084 buf_init(&bb, buf_o, sizeof(buf_o));
1085 if (decryptrest(kx, kxc, KX_SWITCHOK, b))
1087 if ((hswok = buf_get(b, algs.hashsz)) == 0 || BLEFT(b)) {
1088 a_warn("KX", "?PEER", kx->p, "invalid", "switch-ok", A_END);
1091 IF_TRACING(T_KEYEXCH, {
1092 trace_block(T_CRYPTO, "crypto: switch confirmation hash",
1093 hswok, algs.hashsz);
1095 if (memcmp(hswok, kxc->hswok_in, algs.hashsz) != 0) {
1096 a_warn("KX", "?PEER", kx->p, "incorrect", "switch-ok", A_END);
1099 if (kx->s < KXS_SWITCH)
1107 /*----- Main code ---------------------------------------------------------*/
1111 * Arguments: @keyexch *kx@ = pointer to key exchange context
1115 * Use: Stops a key exchange dead in its tracks. Throws away all of
1116 * the context information. The context is left in an
1117 * inconsistent state. The only functions which understand this
1118 * state are @kx_free@ and @kx_init@ (which cause it internally
1119 * it), and @start@ (which expects it to be the prevailing
1123 static void stop(keyexch *kx)
1127 if (kx->f & KXF_DEAD)
1130 if (kx->f & KXF_TIMER)
1131 sel_rmtimer(&kx->t);
1132 for (i = 0; i < kx->nr; i++)
1133 kxc_destroy(kx->r[i]);
1135 G_DESTROY(gg, kx->c);
1136 G_DESTROY(gg, kx->rx);
1139 kx->f &= ~KXF_TIMER;
1142 /* --- @start@ --- *
1144 * Arguments: @keyexch *kx@ = pointer to key exchange context
1145 * @time_t now@ = the current time
1149 * Use: Starts a new key exchange with the peer. The context must be
1150 * in the bizarre state left by @stop@ or @kx_init@.
1153 static void start(keyexch *kx, time_t now)
1157 assert(kx->f & KXF_DEAD);
1159 kx->f &= ~(KXF_DEAD | KXF_CORK);
1161 kx->alpha = mprand_range(MP_NEW, gg->r, &rand_global, 0);
1162 kx->c = G_CREATE(gg); G_EXP(gg, kx->c, gg->g, kx->alpha);
1163 kx->rx = G_CREATE(gg); G_EXP(gg, kx->rx, kx->kpub, kx->alpha);
1165 kx->t_valid = now + T_VALID;
1167 h = GH_INIT(algs.h);
1168 HASH_STRING(h, "tripe-cookie");
1173 IF_TRACING(T_KEYEXCH, {
1174 trace(T_KEYEXCH, "keyexch: creating new challenge");
1175 IF_TRACING(T_CRYPTO, {
1176 trace(T_CRYPTO, "crypto: secret = %s", mpstr(kx->alpha));
1177 trace(T_CRYPTO, "crypto: challenge = %s", gestr(gg, kx->c));
1178 trace(T_CRYPTO, "crypto: expected response = %s", gestr(gg, kx->rx));
1179 trace_block(T_CRYPTO, "crypto: challenge cookie", kx->hc, algs.hashsz);
1184 /* --- @checkpub@ --- *
1186 * Arguments: @keyexch *kx@ = pointer to key exchange context
1188 * Returns: Zero if OK, nonzero if the peer's public key has expired.
1190 * Use: Deactivates the key-exchange until the peer acquires a new
1194 static int checkpub(keyexch *kx)
1197 if (kx->f & KXF_DEAD)
1200 if (KEY_EXPIRED(now, kx->texp_kpub)) {
1202 a_warn("KX", "?PEER", kx->p, "public-key-expired", A_END);
1203 G_COPY(gg, kx->kpub, gg->i);
1204 kx->f &= ~KXF_PUBKEY;
1210 /* --- @kx_start@ --- *
1212 * Arguments: @keyexch *kx@ = pointer to key exchange context
1213 * @int forcep@ = nonzero to ignore the quiet timer
1217 * Use: Stimulates a key exchange. If a key exchage is in progress,
1218 * a new challenge is sent (unless the quiet timer forbids
1219 * this); if no exchange is in progress, one is commenced.
1222 void kx_start(keyexch *kx, int forcep)
1224 time_t now = time(0);
1228 if (forcep || !VALIDP(kx, now)) {
1231 a_notify("KXSTART", "?PEER", kx->p, A_END);
1236 /* --- @kx_message@ --- *
1238 * Arguments: @keyexch *kx@ = pointer to key exchange context
1239 * @unsigned msg@ = the message code
1240 * @buf *b@ = pointer to buffer containing the packet
1244 * Use: Reads a packet containing key exchange messages and handles
1248 void kx_message(keyexch *kx, unsigned msg, buf *b)
1250 struct timeval now, tv;
1251 stats *st = p_stats(kx->p);
1255 gettimeofday(&now, 0);
1257 if (kx->f & KXF_CORK) {
1258 start(kx, now.tv_sec);
1259 rs_time(&kx->rs, &tv, &now);
1261 a_notify("KXSTART", A_END);
1267 if (!VALIDP(kx, now.tv_sec)) {
1269 start(kx, now.tv_sec);
1271 T( trace(T_KEYEXCH, "keyexch: processing %s packet from `%s'",
1272 msg < KX_NMSG ? pkname[msg] : "unknown", p_name(kx->p)); )
1276 rc = doprechallenge(kx, b);
1279 rc = dochallenge(kx, b);
1282 rc = doreply(kx, b);
1285 rc = doswitch(kx, b);
1288 rc = doswitchok(kx, b);
1291 a_warn("KX", "?PEER", kx->p, "unknown-message", "0x%02x", msg, A_END);
1304 /* --- @kx_free@ --- *
1306 * Arguments: @keyexch *kx@ = pointer to key exchange context
1310 * Use: Frees everything in a key exchange context.
1313 void kx_free(keyexch *kx)
1316 G_DESTROY(gg, kx->kpub);
1319 /* --- @kx_newkeys@ --- *
1321 * Arguments: @keyexch *kx@ = pointer to key exchange context
1325 * Use: Informs the key exchange module that its keys may have
1326 * changed. If fetching the new keys fails, the peer will be
1327 * destroyed, we log messages and struggle along with the old
1331 void kx_newkeys(keyexch *kx)
1333 if (km_getpubkey(p_tag(kx->p), kx->kpub, &kx->texp_kpub))
1335 kx->f |= KXF_PUBKEY;
1336 if ((kx->f & KXF_DEAD) || kx->s != KXS_SWITCH) {
1337 T( trace(T_KEYEXCH, "keyexch: restarting key negotiation with `%s'",
1345 /* --- @kx_init@ --- *
1347 * Arguments: @keyexch *kx@ = pointer to key exchange context
1348 * @peer *p@ = pointer to peer context
1349 * @keyset **ks@ = pointer to keyset list
1350 * @unsigned f@ = various useful flags
1352 * Returns: Zero if OK, nonzero if it failed.
1354 * Use: Initializes a key exchange module. The module currently
1355 * contains no keys, and will attempt to initiate a key
1359 int kx_init(keyexch *kx, peer *p, keyset **ks, unsigned f)
1363 kx->kpub = G_CREATE(gg);
1364 if (km_getpubkey(p_tag(p), kx->kpub, &kx->texp_kpub)) {
1365 G_DESTROY(gg, kx->kpub);
1368 kx->f = KXF_DEAD | KXF_PUBKEY | f;
1370 if (!(kx->f & KXF_CORK)) {
1373 /* Don't notify here: the ADD message hasn't gone out yet. */
1378 /*----- That's all, folks -------------------------------------------------*/