3 * $Id: keyset.c,v 1.9 2003/10/15 09:29:38 mdw Exp $
5 * Handling of symmetric keysets
7 * (c) 2001 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Trivial IP Encryption (TrIPE).
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.
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.
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.
29 /*----- Revision history --------------------------------------------------*
32 * Revision 1.9 2003/10/15 09:29:38 mdw
33 * Cosmetic fix to changelog comment.
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
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
45 * Revision 1.6 2003/04/06 10:26:35 mdw
46 * Report peer name on decrypt errors.
48 * Revision 1.5 2001/06/19 22:07:43 mdw
49 * Change the encrypted packet format to be non-malleable.
51 * Revision 1.4 2001/06/16 14:06:40 mdw
52 * Quantify collision probabilities for the stated data volume bounds.
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.
59 * Revision 1.2 2001/02/05 19:53:23 mdw
60 * Add sequence number protection.
62 * Revision 1.1 2001/02/03 20:26:37 mdw
67 /*----- Header files ------------------------------------------------------*/
71 /*----- Tunable parameters ------------------------------------------------*/
73 /* --- Note on size limits --- *
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 %$2^{-19}$%.
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 */
85 /*----- Handy macros ------------------------------------------------------*/
87 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
89 /*----- Low-level packet encryption and decryption ------------------------*/
91 /* --- Encrypted data format --- *
93 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
96 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
98 * as the CBC-ciphertext of %$p_i$%, and then
100 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
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].
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].
115 /* --- @doencrypt@ --- *
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
122 * Returns: Zero if OK, nonzero if a new key is required.
124 * Use: Encrypts a message with the given key. We assume that the
125 * keyset is OK to use.
128 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
132 const octet *p = BCUR(b);
133 size_t sz = BLEFT(b);
134 octet *qmac, *qseq, *qiv, *qpk;
140 /* --- Allocate the required buffer space --- */
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);
149 /* --- Encrypt the packet --- */
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);
161 /* --- Now compute the MAC --- */
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);
168 IF_TRACING(T_KEYSET, {
169 trace_block(T_CRYPTO, "crypto: computed MAC", qmac, MACSZ);
172 /* --- Deduct the packet size from the key's data life --- */
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); )
188 /* --- @dodecrypt@ --- *
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
196 * Returns: Zero if OK, nonzero if it failed.
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@.
206 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
208 const octet *pmac, *piv, *pseq, *ppk;
209 size_t psz = BLEFT(b);
213 gcipher *c = ks->cin;
214 size_t ivsz = c->ops->c->blksz;
219 /* --- Break up the packet into its components --- */
221 if (psz < ivsz + 4) {
222 T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
225 sz = psz - IVSZ - SEQSZ - MACSZ;
226 pmac = BCUR(b); pseq = pmac + MACSZ; piv = pseq + SEQSZ; ppk = piv + IVSZ;
229 /* --- Verify the MAC on the packet --- */
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);
242 IF_TRACING(T_KEYSET, {
243 trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
244 trace_block(T_CRYPTO, "crypto: expected MAC", pmac, MACSZ);
249 /* --- Decrypt the packet --- */
251 c->ops->setiv(c, piv);
252 c->ops->decrypt(c, ppk, q, sz);
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);
264 /* --- @dosequence@ --- *
266 * Arguments: @keyset *ks@ = pointer to a keyset
267 * @uint32 seq@ = a sequence number from a packet
269 * Returns: Zero if the sequence number is OK, nonzero if it's not.
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.
277 static int dosequence(keyset *ks, uint32 seq)
282 if (seq < ks->iseq) {
283 a_warn("received packet has old sequence number (possible replay)");
286 if (seq >= ks->iseq + KS_SEQWINSZ) {
287 n = seq - (ks->iseq + KS_SEQWINSZ - 1);
294 seqbit = 1 << (seq - ks->iseq);
295 if (ks->iwin & seqbit) {
296 a_warn("received packet repeats old sequence number");
303 /*----- Operations on a single keyset -------------------------------------*/
305 /* --- @ks_drop@ --- *
307 * Arguments: @keyset *ks@ = pointer to a keyset
311 * Use: Decrements a keyset's reference counter. If the counter hits
312 * zero, the keyset is freed.
315 void ks_drop(keyset *ks)
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);
326 /* --- @ks_gen@ --- *
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
332 * Returns: A pointer to the new keyset.
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.
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.
349 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
353 keyset *ks = CREATE(keyset);
354 time_t now = time(0);
356 T( static unsigned seq = 0; )
358 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
360 /* --- Construct the various keys --- *
362 * This is done with macros, because it's quite tedious.
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)
369 #define IN MINE; YOURS; OURS
370 #define OUT YOURS; MINE; OURS
371 #define STR_IN "incoming"
372 #define STR_OUT "outgoing"
374 #define GETHASH(str, dir) do { \
376 HASH_STRING(&h, "tripe-" str); \
378 HASH_DONE(&h, buf); \
379 IF_TRACING(T_KEYSET, { \
380 trace_block(T_CRYPTO, "crypto: " STR_##dir " key " str, \
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));
399 T( ks->seq = seq++; )
401 ks->t_exp = now + T_EXP;
403 ks->oseq = ks->iseq = 0;
412 /* --- @ks_tregen@ --- *
414 * Arguments: @keyset *ks@ = pointer to a keyset
416 * Returns: The time at which moves ought to be made to replace this key.
419 time_t ks_tregen(keyset *ks) { return (ks->t_exp - T_EXP + T_REGEN); }
421 /* --- @ks_activate@ --- *
423 * Arguments: @keyset *ks@ = pointer to a keyset
427 * Use: Activates a keyset, so that it can be used for encrypting
431 void ks_activate(keyset *ks)
433 if (ks->f & KSF_LISTEN) {
434 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
435 ks->f &= ~KSF_LISTEN;
439 /* --- @ks_encrypt@ --- *
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
446 * Returns: Zero if OK, nonzero if the key needs replacing. If the
447 * encryption failed, the output buffer is broken and zero is
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.
456 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
458 time_t now = time(0);
460 if (!KEYOK(ks, now)) {
464 return (doencrypt(ks, ty, b, bb));
467 /* --- @ks_decrypt@ --- *
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
474 * Returns: Zero on success, or nonzero if there was some problem.
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.
481 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
483 time_t now = time(0);
486 if (!KEYOK(ks, now) ||
487 buf_ensure(bb, BLEN(b)) ||
488 dodecrypt(ks, ty, b, bb, &seq) ||
494 /*----- Keyset list handling ----------------------------------------------*/
496 /* --- @ksl_free@ --- *
498 * Arguments: @keyset **ksroot@ = pointer to keyset list head
502 * Use: Frees (releases references to) all of the keys in a keyset.
505 void ksl_free(keyset **ksroot)
508 for (ks = *ksroot; ks; ks = ksn) {
515 /* --- @ksl_link@ --- *
517 * Arguments: @keyset **ksroot@ = pointer to keyset list head
518 * @keyset *ks@ = pointer to a keyset
522 * Use: Links a keyset into a list. A keyset can only be on one list
523 * at a time. Bad things happen otherwise.
526 void ksl_link(keyset **ksroot, keyset *ks)
528 assert(!(ks->f & KSF_LINK));
535 /* --- @ksl_prune@ --- *
537 * Arguments: @keyset **ksroot@ = pointer to keyset list head
541 * Use: Prunes the keyset list by removing keys which mustn't be used
545 void ksl_prune(keyset **ksroot)
547 time_t now = time(0);
550 keyset *ks = *ksroot;
552 if (ks->t_exp <= now) {
553 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
556 } else if (ks->sz_exp == 0) {
557 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
572 /* --- @ksl_encrypt@ --- *
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
579 * Returns: Nonzero if a new key is needed.
581 * Use: Encrypts a packet.
584 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
586 time_t now = time(0);
587 keyset *ks = *ksroot;
591 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
595 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
600 return (doencrypt(ks, ty, b, bb));
603 /* --- @ksl_decrypt@ --- *
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
610 * Returns: Nonzero if the packet couldn't be decrypted.
612 * Use: Decrypts a packet.
615 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
617 time_t now = time(0);
621 if (buf_ensure(bb, BLEN(b)))
624 for (ks = *ksroot; ks; ks = ks->next) {
627 if (!dodecrypt(ks, ty, b, bb, &seq)) {
628 if (ks->f & KSF_LISTEN) {
629 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
631 ks->f &= ~KSF_LISTEN;
633 return (dosequence(ks, seq));
636 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
640 /*----- That's all, folks -------------------------------------------------*/