Remove buf, and add Ethereal analysis.
[tripe] / keyset.c
1 /* -*-c-*-
2 *
3 * $Id: keyset.c,v 1.9 2003/10/15 09:29:38 mdw Exp $
4 *
5 * Handling of symmetric keysets
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: keyset.c,v $
32 * Revision 1.9 2003/10/15 09:29:38 mdw
33 * Cosmetic fix to changelog comment.
34 *
35 * Revision 1.8 2003/07/13 11:19:49 mdw
36 * Incompatible protocol fix! Include message type code under MAC tag to
37 * prevent cut-and-paste from key-exchange messages to general packet
38 * transport.
39 *
40 * Revision 1.7 2003/05/17 11:00:47 mdw
41 * Don't make scary messages just because one key didn't work on a message:
42 * only be frightened if they all fail. Set initial keyset refcount
43 * correctly.
44 *
45 * Revision 1.6 2003/04/06 10:26:35 mdw
46 * Report peer name on decrypt errors.
47 *
48 * Revision 1.5 2001/06/19 22:07:43 mdw
49 * Change the encrypted packet format to be non-malleable.
50 *
51 * Revision 1.4 2001/06/16 14:06:40 mdw
52 * Quantify collision probabilities for the stated data volume bounds.
53 *
54 * Revision 1.3 2001/02/16 21:39:55 mdw
55 * Major overhaul. Separate functions for manipulating keysets from
56 * functions for manipulating keyset lists. Introduce a concept of
57 * listening-only keys.
58 *
59 * Revision 1.2 2001/02/05 19:53:23 mdw
60 * Add sequence number protection.
61 *
62 * Revision 1.1 2001/02/03 20:26:37 mdw
63 * Initial checkin.
64 *
65 */
66
67 /*----- Header files ------------------------------------------------------*/
68
69 #include "tripe.h"
70
71 /*----- Tunable parameters ------------------------------------------------*/
72
73 /* --- Note on size limits --- *
74 *
75 * For a 64-bit block cipher (e.g., Blowfish), the probability of a collision
76 * occurring after 32 MB is less than %$2^{-21}$%, and the probability of a
77 * collision occurring after 64 MB is less than %$2^{-19}$%.
78 */
79
80 #define T_EXP MIN(60) /* Expiry time for a key */
81 #define T_REGEN MIN(45) /* Regeneration time for a key */
82 #define SZ_EXP MEG(64) /* Expiry data size for a key */
83 #define SZ_REGEN MEG(32) /* Data size threshold for regen */
84
85 /*----- Handy macros ------------------------------------------------------*/
86
87 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
88
89 /*----- Low-level packet encryption and decryption ------------------------*/
90
91 /* --- Encrypted data format --- *
92 *
93 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
94 * compute
95 *
96 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
97 *
98 * as the CBC-ciphertext of %$p_i$%, and then
99 *
100 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
101 *
102 * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
103 * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
104 * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
105 * [Bellare and Namprempre].
106 *
107 * This also ensures that, assuming the key is good, we have a secure channel
108 * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
109 * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
110 * then-encrypt scheme and still have a secure channel. However, I like the
111 * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
112 * the Horton Principle [Wagner and Schneier].
113 */
114
115 /* --- @doencrypt@ --- *
116 *
117 * Arguments: @keyset *ks@ = pointer to keyset to use
118 * @unsigned ty@ = type of message this is
119 * @buf *b@ = pointer to an input buffer
120 * @buf *bb@ = pointer to an output buffer
121 *
122 * Returns: Zero if OK, nonzero if a new key is required.
123 *
124 * Use: Encrypts a message with the given key. We assume that the
125 * keyset is OK to use.
126 */
127
128 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
129 {
130 ghash *h;
131 gcipher *c;
132 const octet *p = BCUR(b);
133 size_t sz = BLEFT(b);
134 octet *qmac, *qseq, *qiv, *qpk;
135 uint32 oseq;
136 size_t osz, nsz;
137 octet t[4];
138 int rc = 0;
139
140 /* --- Allocate the required buffer space --- */
141
142 c = ks->cout;
143 if (buf_ensure(bb, MACSZ + SEQSZ + IVSZ + sz))
144 return (0); /* Caution! */
145 qmac = BCUR(bb); qseq = qmac + MACSZ; qiv = qseq + SEQSZ; qpk = qiv + IVSZ;
146 BSTEP(bb, MACSZ + SEQSZ + IVSZ + sz);
147 STORE32(t, ty);
148
149 /* --- Encrypt the packet --- */
150
151 oseq = ks->oseq++; STORE32(qseq, oseq);
152 rand_get(RAND_GLOBAL, qiv, IVSZ);
153 c->ops->setiv(c, qiv);
154 c->ops->encrypt(c, p, qpk, sz);
155 IF_TRACING(T_KEYSET, {
156 trace(T_KEYSET, "keyset: encrypting packet %lu using keyset %u",
157 (unsigned long)oseq, ks->seq);
158 trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
159 })
160
161 /* --- Now compute the MAC --- */
162
163 h = ks->mout->ops->init(ks->mout);
164 h->ops->hash(h, t, sizeof(t));
165 h->ops->hash(h, qseq, SEQSZ + IVSZ + sz);
166 memcpy(qmac, h->ops->done(h, 0), MACSZ);
167 h->ops->destroy(h);
168 IF_TRACING(T_KEYSET, {
169 trace_block(T_CRYPTO, "crypto: computed MAC", qmac, MACSZ);
170 })
171
172 /* --- Deduct the packet size from the key's data life --- */
173
174 osz = ks->sz_exp;
175 if (osz > sz)
176 nsz = osz - sz;
177 else
178 nsz = 0;
179 if (osz >= SZ_REGEN && nsz < SZ_REGEN) {
180 T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
181 "forcing exchange", ks->seq); )
182 rc = -1;
183 }
184 ks->sz_exp = nsz;
185 return (rc);
186 }
187
188 /* --- @dodecrypt@ --- *
189 *
190 * Arguments: @keyset *ks@ = pointer to keyset to use
191 * @unsigned ty@ = expected type code
192 * @buf *b@ = pointer to an input buffer
193 * @buf *bb@ = pointer to an output buffer
194 * @uint32 *seq@ = where to store the sequence number
195 *
196 * Returns: Zero if OK, nonzero if it failed.
197 *
198 * Use: Attempts to decrypt a message with the given key. No other
199 * checking (e.g., sequence number checks) is performed. We
200 * assume that the keyset is OK to use, and that there is
201 * sufficient output buffer space reserved. If the decryption
202 * is successful, the buffer pointer is moved past the decrypted
203 * packet, and the packet's sequence number is stored in @*seq@.
204 */
205
206 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
207 {
208 const octet *pmac, *piv, *pseq, *ppk;
209 size_t psz = BLEFT(b);
210 size_t sz;
211 octet *q = BCUR(bb);
212 ghash *h;
213 gcipher *c = ks->cin;
214 size_t ivsz = c->ops->c->blksz;
215 octet *mac;
216 int eq;
217 octet t[4];
218
219 /* --- Break up the packet into its components --- */
220
221 if (psz < ivsz + 4) {
222 T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
223 return (-1);
224 }
225 sz = psz - IVSZ - SEQSZ - MACSZ;
226 pmac = BCUR(b); pseq = pmac + MACSZ; piv = pseq + SEQSZ; ppk = piv + IVSZ;
227 STORE32(t, ty);
228
229 /* --- Verify the MAC on the packet --- */
230
231 h = ks->min->ops->init(ks->min);
232 h->ops->hash(h, t, sizeof(t));
233 h->ops->hash(h, pseq, SEQSZ + IVSZ + sz);
234 mac = h->ops->done(h, 0);
235 eq = !memcmp(mac, pmac, MACSZ);
236 IF_TRACING(T_KEYSET, {
237 trace(T_KEYSET, "keyset: decrypting using keyset %u", ks->seq);
238 trace_block(T_CRYPTO, "crypto: computed MAC", mac, MACSZ);
239 })
240 h->ops->destroy(h);
241 if (!eq) {
242 IF_TRACING(T_KEYSET, {
243 trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
244 trace_block(T_CRYPTO, "crypto: expected MAC", pmac, MACSZ);
245 })
246 return (-1);
247 }
248
249 /* --- Decrypt the packet --- */
250
251 c->ops->setiv(c, piv);
252 c->ops->decrypt(c, ppk, q, sz);
253 if (seq)
254 *seq = LOAD32(pseq);
255 IF_TRACING(T_KEYSET, {
256 trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
257 (unsigned long)LOAD32(pseq));
258 trace_block(T_CRYPTO, "crypto: decrypted packet", q, sz);
259 })
260 BSTEP(bb, sz);
261 return (0);
262 }
263
264 /* --- @dosequence@ --- *
265 *
266 * Arguments: @keyset *ks@ = pointer to a keyset
267 * @uint32 seq@ = a sequence number from a packet
268 *
269 * Returns: Zero if the sequence number is OK, nonzero if it's not.
270 *
271 * Use: Checks a sequence number. The data in the keyset which keeps
272 * track of valid sequence numbers is updated if the sequence
273 * number given is good. It's assumed that the sequence number
274 * has already been checked for authenticity.
275 */
276
277 static int dosequence(keyset *ks, uint32 seq)
278 {
279 uint32 seqbit;
280 uint32 n;
281
282 if (seq < ks->iseq) {
283 a_warn("received packet has old sequence number (possible replay)");
284 return (-1);
285 }
286 if (seq >= ks->iseq + KS_SEQWINSZ) {
287 n = seq - (ks->iseq + KS_SEQWINSZ - 1);
288 if (n < KS_SEQWINSZ)
289 ks->iwin >>= n;
290 else
291 ks->iwin = 0;
292 ks->iseq += n;
293 }
294 seqbit = 1 << (seq - ks->iseq);
295 if (ks->iwin & seqbit) {
296 a_warn("received packet repeats old sequence number");
297 return (-1);
298 }
299 ks->iwin |= seqbit;
300 return (0);
301 }
302
303 /*----- Operations on a single keyset -------------------------------------*/
304
305 /* --- @ks_drop@ --- *
306 *
307 * Arguments: @keyset *ks@ = pointer to a keyset
308 *
309 * Returns: ---
310 *
311 * Use: Decrements a keyset's reference counter. If the counter hits
312 * zero, the keyset is freed.
313 */
314
315 void ks_drop(keyset *ks)
316 {
317 if (--ks->ref)
318 return;
319 ks->cin->ops->destroy(ks->cin);
320 ks->cout->ops->destroy(ks->cout);
321 ks->min->ops->destroy(ks->min);
322 ks->mout->ops->destroy(ks->mout);
323 DESTROY(ks);
324 }
325
326 /* --- @ks_gen@ --- *
327 *
328 * Arguments: @const void *k@ = pointer to key material
329 * @size_t x, y, z@ = offsets into key material (see below)
330 * @peer *p@ = pointer to peer information
331 *
332 * Returns: A pointer to the new keyset.
333 *
334 * Use: Derives a new keyset from the given key material. The
335 * offsets @x@, @y@ and @z@ separate the key material into three
336 * parts. Between the @k@ and @k + x@ is `my' contribution to
337 * the key material; between @k + x@ and @k + y@ is `your'
338 * contribution; and between @k + y@ and @k + z@ is a shared
339 * value we made together. These are used to construct two
340 * pairs of symmetric keys. Each pair consists of an encryption
341 * key and a message authentication key. One pair is used for
342 * outgoing messages, the other for incoming messages.
343 *
344 * The new key is marked so that it won't be selected for output
345 * by @ksl_encrypt@. You can still encrypt data with it by
346 * calling @ks_encrypt@ directly.
347 */
348
349 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
350 {
351 HASH_CTX h;
352 octet buf[HASHSZ];
353 keyset *ks = CREATE(keyset);
354 time_t now = time(0);
355 const octet *pp = k;
356 T( static unsigned seq = 0; )
357
358 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
359
360 /* --- Construct the various keys --- *
361 *
362 * This is done with macros, because it's quite tedious.
363 */
364
365 #define MINE HASH(&h, pp, x)
366 #define YOURS HASH(&h, pp + x, y - x)
367 #define OURS HASH(&h, pp + y, z - y)
368
369 #define IN MINE; YOURS; OURS
370 #define OUT YOURS; MINE; OURS
371 #define STR_IN "incoming"
372 #define STR_OUT "outgoing"
373
374 #define GETHASH(str, dir) do { \
375 HASH_INIT(&h); \
376 HASH_STRING(&h, "tripe-" str); \
377 dir; \
378 HASH_DONE(&h, buf); \
379 IF_TRACING(T_KEYSET, { \
380 trace_block(T_CRYPTO, "crypto: " STR_##dir " key " str, \
381 buf, sizeof(buf)); \
382 }) \
383 } while (0)
384
385 GETHASH("encryption", IN); ks->cin = CIPHER->init(buf, sizeof(buf));
386 GETHASH("integrity", IN); ks->min = MAC->key(buf, sizeof(buf));
387 GETHASH("encryption", OUT); ks->cout = CIPHER->init(buf, sizeof(buf));
388 GETHASH("integrity", OUT); ks->mout = MAC->key(buf, sizeof(buf));
389
390 #undef MINE
391 #undef YOURS
392 #undef OURS
393 #undef IN
394 #undef OUT
395 #undef STR_IN
396 #undef STR_OUT
397 #undef GETHASH
398
399 T( ks->seq = seq++; )
400 ks->ref = 1;
401 ks->t_exp = now + T_EXP;
402 ks->sz_exp = SZ_EXP;
403 ks->oseq = ks->iseq = 0;
404 ks->iwin = 0;
405 ks->next = 0;
406 ks->p = p;
407 ks->f = KSF_LISTEN;
408 BURN(buf);
409 return (ks);
410 }
411
412 /* --- @ks_tregen@ --- *
413 *
414 * Arguments: @keyset *ks@ = pointer to a keyset
415 *
416 * Returns: The time at which moves ought to be made to replace this key.
417 */
418
419 time_t ks_tregen(keyset *ks) { return (ks->t_exp - T_EXP + T_REGEN); }
420
421 /* --- @ks_activate@ --- *
422 *
423 * Arguments: @keyset *ks@ = pointer to a keyset
424 *
425 * Returns: ---
426 *
427 * Use: Activates a keyset, so that it can be used for encrypting
428 * outgoing messages.
429 */
430
431 void ks_activate(keyset *ks)
432 {
433 if (ks->f & KSF_LISTEN) {
434 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
435 ks->f &= ~KSF_LISTEN;
436 }
437 }
438
439 /* --- @ks_encrypt@ --- *
440 *
441 * Arguments: @keyset *ks@ = pointer to a keyset
442 * @unsigned ty@ = message type
443 * @buf *b@ = pointer to input buffer
444 * @buf *bb@ = pointer to output buffer
445 *
446 * Returns: Zero if OK, nonzero if the key needs replacing. If the
447 * encryption failed, the output buffer is broken and zero is
448 * returned.
449 *
450 * Use: Encrypts a block of data using the key. Note that the `key
451 * ought to be replaced' notification is only ever given once
452 * for each key. Also note that this call forces a keyset to be
453 * used even if it's marked as not for data output.
454 */
455
456 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
457 {
458 time_t now = time(0);
459
460 if (!KEYOK(ks, now)) {
461 buf_break(bb);
462 return (0);
463 }
464 return (doencrypt(ks, ty, b, bb));
465 }
466
467 /* --- @ks_decrypt@ --- *
468 *
469 * Arguments: @keyset *ks@ = pointer to a keyset
470 * @unsigned ty@ = expected type code
471 * @buf *b@ = pointer to an input buffer
472 * @buf *bb@ = pointer to an output buffer
473 *
474 * Returns: Zero on success, or nonzero if there was some problem.
475 *
476 * Use: Attempts to decrypt a message using a given key. Note that
477 * requesting decryption with a key directly won't clear a
478 * marking that it's not for encryption.
479 */
480
481 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
482 {
483 time_t now = time(0);
484 uint32 seq;
485
486 if (!KEYOK(ks, now) ||
487 buf_ensure(bb, BLEN(b)) ||
488 dodecrypt(ks, ty, b, bb, &seq) ||
489 dosequence(ks, seq))
490 return (-1);
491 return (0);
492 }
493
494 /*----- Keyset list handling ----------------------------------------------*/
495
496 /* --- @ksl_free@ --- *
497 *
498 * Arguments: @keyset **ksroot@ = pointer to keyset list head
499 *
500 * Returns: ---
501 *
502 * Use: Frees (releases references to) all of the keys in a keyset.
503 */
504
505 void ksl_free(keyset **ksroot)
506 {
507 keyset *ks, *ksn;
508 for (ks = *ksroot; ks; ks = ksn) {
509 ksn = ks->next;
510 ks->f &= ~KSF_LINK;
511 ks_drop(ks);
512 }
513 }
514
515 /* --- @ksl_link@ --- *
516 *
517 * Arguments: @keyset **ksroot@ = pointer to keyset list head
518 * @keyset *ks@ = pointer to a keyset
519 *
520 * Returns: ---
521 *
522 * Use: Links a keyset into a list. A keyset can only be on one list
523 * at a time. Bad things happen otherwise.
524 */
525
526 void ksl_link(keyset **ksroot, keyset *ks)
527 {
528 assert(!(ks->f & KSF_LINK));
529 ks->next = *ksroot;
530 *ksroot = ks;
531 ks->f |= KSF_LINK;
532 ks->ref++;
533 }
534
535 /* --- @ksl_prune@ --- *
536 *
537 * Arguments: @keyset **ksroot@ = pointer to keyset list head
538 *
539 * Returns: ---
540 *
541 * Use: Prunes the keyset list by removing keys which mustn't be used
542 * any more.
543 */
544
545 void ksl_prune(keyset **ksroot)
546 {
547 time_t now = time(0);
548
549 while (*ksroot) {
550 keyset *ks = *ksroot;
551
552 if (ks->t_exp <= now) {
553 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
554 ks->seq); )
555 goto kill;
556 } else if (ks->sz_exp == 0) {
557 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
558 ks->seq); )
559 goto kill;
560 } else {
561 ksroot = &ks->next;
562 continue;
563 }
564
565 kill:
566 *ksroot = ks->next;
567 ks->f &= ~KSF_LINK;
568 ks_drop(ks);
569 }
570 }
571
572 /* --- @ksl_encrypt@ --- *
573 *
574 * Arguments: @keyset **ksroot@ = pointer to keyset list head
575 * @unsigned ty@ = message type
576 * @buf *b@ = pointer to input buffer
577 * @buf *bb@ = pointer to output buffer
578 *
579 * Returns: Nonzero if a new key is needed.
580 *
581 * Use: Encrypts a packet.
582 */
583
584 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
585 {
586 time_t now = time(0);
587 keyset *ks = *ksroot;
588
589 for (;;) {
590 if (!ks) {
591 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
592 buf_break(bb);
593 return (-1);
594 }
595 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
596 break;
597 ks = ks->next;
598 }
599
600 return (doencrypt(ks, ty, b, bb));
601 }
602
603 /* --- @ksl_decrypt@ --- *
604 *
605 * Arguments: @keyset **ksroot@ = pointer to keyset list head
606 * @unsigned ty@ = expected type code
607 * @buf *b@ = pointer to input buffer
608 * @buf *bb@ = pointer to output buffer
609 *
610 * Returns: Nonzero if the packet couldn't be decrypted.
611 *
612 * Use: Decrypts a packet.
613 */
614
615 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
616 {
617 time_t now = time(0);
618 keyset *ks;
619 uint32 seq;
620
621 if (buf_ensure(bb, BLEN(b)))
622 return (-1);
623
624 for (ks = *ksroot; ks; ks = ks->next) {
625 if (!KEYOK(ks, now))
626 continue;
627 if (!dodecrypt(ks, ty, b, bb, &seq)) {
628 if (ks->f & KSF_LISTEN) {
629 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
630 ks->seq); )
631 ks->f &= ~KSF_LISTEN;
632 }
633 return (dosequence(ks, seq));
634 }
635 }
636 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
637 return (-1);
638 }
639
640 /*----- That's all, folks -------------------------------------------------*/