3 * $Id: keyset.c,v 1.8 2003/07/13 11:19:49 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 1.8 2003/07/13 11:19:49 mdw
33 * Incopatible protocol fix! Include message type code under MAC tag to prevent
34 * cut-and-paste from key-exchange messages to general packet transport.
36 * Revision 1.7 2003/05/17 11:00:47 mdw
37 * Don't make scary messages just because one key didn't work on a message:
38 * only be frightened if they all fail. Set initial keyset refcount
41 * Revision 1.6 2003/04/06 10:26:35 mdw
42 * Report peer name on decrypt errors.
44 * Revision 1.5 2001/06/19 22:07:43 mdw
45 * Change the encrypted packet format to be non-malleable.
47 * Revision 1.4 2001/06/16 14:06:40 mdw
48 * Quantify collision probabilities for the stated data volume bounds.
50 * Revision 1.3 2001/02/16 21:39:55 mdw
51 * Major overhaul. Separate functions for manipulating keysets from
52 * functions for manipulating keyset lists. Introduce a concept of
53 * listening-only keys.
55 * Revision 1.2 2001/02/05 19:53:23 mdw
56 * Add sequence number protection.
58 * Revision 1.1 2001/02/03 20:26:37 mdw
63 /*----- Header files ------------------------------------------------------*/
67 /*----- Tunable parameters ------------------------------------------------*/
69 /* --- Note on size limits --- *
71 * For a 64-bit block cipher (e.g., Blowfish), the probability of a collision
72 * occurring after 32 MB is less than %$2^{-21}$%, and the probability of a
73 * collision occurring after 64 MB is less than %$2^{-19}$%.
76 #define T_EXP MIN(60) /* Expiry time for a key */
77 #define T_REGEN MIN(45) /* Regeneration time for a key */
78 #define SZ_EXP MEG(64) /* Expiry data size for a key */
79 #define SZ_REGEN MEG(32) /* Data size threshold for regen */
81 /*----- Handy macros ------------------------------------------------------*/
83 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
85 /*----- Low-level packet encryption and decryption ------------------------*/
87 /* --- Encrypted data format --- *
89 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
92 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
94 * as the CBC-ciphertext of %$p_i$%, and then
96 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
98 * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
99 * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
100 * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
101 * [Bellare and Namprempre].
103 * This also ensures that, assuming the key is good, we have a secure channel
104 * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
105 * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
106 * then-encrypt scheme and still have a secure channel. However, I like the
107 * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
108 * the Horton Principle [Wagner and Schneier].
111 /* --- @doencrypt@ --- *
113 * Arguments: @keyset *ks@ = pointer to keyset to use
114 * @unsigned ty@ = type of message this is
115 * @buf *b@ = pointer to an input buffer
116 * @buf *bb@ = pointer to an output buffer
118 * Returns: Zero if OK, nonzero if a new key is required.
120 * Use: Encrypts a message with the given key. We assume that the
121 * keyset is OK to use.
124 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
128 const octet *p = BCUR(b);
129 size_t sz = BLEFT(b);
130 octet *qmac, *qseq, *qiv, *qpk;
136 /* --- Allocate the required buffer space --- */
139 if (buf_ensure(bb, MACSZ + SEQSZ + IVSZ + sz))
140 return (0); /* Caution! */
141 qmac = BCUR(bb); qseq = qmac + MACSZ; qiv = qseq + SEQSZ; qpk = qiv + IVSZ;
142 BSTEP(bb, MACSZ + SEQSZ + IVSZ + sz);
145 /* --- Encrypt the packet --- */
147 oseq = ks->oseq++; STORE32(qseq, oseq);
148 rand_get(RAND_GLOBAL, qiv, IVSZ);
149 c->ops->setiv(c, qiv);
150 c->ops->encrypt(c, p, qpk, sz);
151 IF_TRACING(T_KEYSET, {
152 trace(T_KEYSET, "keyset: encrypting packet %lu using keyset %u",
153 (unsigned long)oseq, ks->seq);
154 trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
157 /* --- Now compute the MAC --- */
159 h = ks->mout->ops->init(ks->mout);
160 h->ops->hash(h, t, sizeof(t));
161 h->ops->hash(h, qseq, SEQSZ + IVSZ + sz);
162 memcpy(qmac, h->ops->done(h, 0), MACSZ);
164 IF_TRACING(T_KEYSET, {
165 trace_block(T_CRYPTO, "crypto: computed MAC", qmac, MACSZ);
168 /* --- Deduct the packet size from the key's data life --- */
175 if (osz >= SZ_REGEN && nsz < SZ_REGEN) {
176 T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
177 "forcing exchange", ks->seq); )
184 /* --- @dodecrypt@ --- *
186 * Arguments: @keyset *ks@ = pointer to keyset to use
187 * @unsigned ty@ = expected type code
188 * @buf *b@ = pointer to an input buffer
189 * @buf *bb@ = pointer to an output buffer
190 * @uint32 *seq@ = where to store the sequence number
192 * Returns: Zero if OK, nonzero if it failed.
194 * Use: Attempts to decrypt a message with the given key. No other
195 * checking (e.g., sequence number checks) is performed. We
196 * assume that the keyset is OK to use, and that there is
197 * sufficient output buffer space reserved. If the decryption
198 * is successful, the buffer pointer is moved past the decrypted
199 * packet, and the packet's sequence number is stored in @*seq@.
202 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
204 const octet *pmac, *piv, *pseq, *ppk;
205 size_t psz = BLEFT(b);
209 gcipher *c = ks->cin;
210 size_t ivsz = c->ops->c->blksz;
215 /* --- Break up the packet into its components --- */
217 if (psz < ivsz + 4) {
218 T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
221 sz = psz - IVSZ - SEQSZ - MACSZ;
222 pmac = BCUR(b); pseq = pmac + MACSZ; piv = pseq + SEQSZ; ppk = piv + IVSZ;
225 /* --- Verify the MAC on the packet --- */
227 h = ks->min->ops->init(ks->min);
228 h->ops->hash(h, t, sizeof(t));
229 h->ops->hash(h, pseq, SEQSZ + IVSZ + sz);
230 mac = h->ops->done(h, 0);
231 eq = !memcmp(mac, pmac, MACSZ);
232 IF_TRACING(T_KEYSET, {
233 trace(T_KEYSET, "keyset: decrypting using keyset %u", ks->seq);
234 trace_block(T_CRYPTO, "crypto: computed MAC", mac, MACSZ);
238 IF_TRACING(T_KEYSET, {
239 trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
240 trace_block(T_CRYPTO, "crypto: expected MAC", pmac, MACSZ);
245 /* --- Decrypt the packet --- */
247 c->ops->setiv(c, piv);
248 c->ops->decrypt(c, ppk, q, sz);
251 IF_TRACING(T_KEYSET, {
252 trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
253 (unsigned long)LOAD32(pseq));
254 trace_block(T_CRYPTO, "crypto: decrypted packet", q, sz);
260 /* --- @dosequence@ --- *
262 * Arguments: @keyset *ks@ = pointer to a keyset
263 * @uint32 seq@ = a sequence number from a packet
265 * Returns: Zero if the sequence number is OK, nonzero if it's not.
267 * Use: Checks a sequence number. The data in the keyset which keeps
268 * track of valid sequence numbers is updated if the sequence
269 * number given is good. It's assumed that the sequence number
270 * has already been checked for authenticity.
273 static int dosequence(keyset *ks, uint32 seq)
278 if (seq < ks->iseq) {
279 a_warn("received packet has old sequence number (possible replay)");
282 if (seq >= ks->iseq + KS_SEQWINSZ) {
283 n = seq - (ks->iseq + KS_SEQWINSZ - 1);
290 seqbit = 1 << (seq - ks->iseq);
291 if (ks->iwin & seqbit) {
292 a_warn("received packet repeats old sequence number");
299 /*----- Operations on a single keyset -------------------------------------*/
301 /* --- @ks_drop@ --- *
303 * Arguments: @keyset *ks@ = pointer to a keyset
307 * Use: Decrements a keyset's reference counter. If the counter hits
308 * zero, the keyset is freed.
311 void ks_drop(keyset *ks)
315 ks->cin->ops->destroy(ks->cin);
316 ks->cout->ops->destroy(ks->cout);
317 ks->min->ops->destroy(ks->min);
318 ks->mout->ops->destroy(ks->mout);
322 /* --- @ks_gen@ --- *
324 * Arguments: @const void *k@ = pointer to key material
325 * @size_t x, y, z@ = offsets into key material (see below)
326 * @peer *p@ = pointer to peer information
328 * Returns: A pointer to the new keyset.
330 * Use: Derives a new keyset from the given key material. The
331 * offsets @x@, @y@ and @z@ separate the key material into three
332 * parts. Between the @k@ and @k + x@ is `my' contribution to
333 * the key material; between @k + x@ and @k + y@ is `your'
334 * contribution; and between @k + y@ and @k + z@ is a shared
335 * value we made together. These are used to construct two
336 * pairs of symmetric keys. Each pair consists of an encryption
337 * key and a message authentication key. One pair is used for
338 * outgoing messages, the other for incoming messages.
340 * The new key is marked so that it won't be selected for output
341 * by @ksl_encrypt@. You can still encrypt data with it by
342 * calling @ks_encrypt@ directly.
345 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
349 keyset *ks = CREATE(keyset);
350 time_t now = time(0);
352 T( static unsigned seq = 0; )
354 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
356 /* --- Construct the various keys --- *
358 * This is done with macros, because it's quite tedious.
361 #define MINE HASH(&h, pp, x)
362 #define YOURS HASH(&h, pp + x, y - x)
363 #define OURS HASH(&h, pp + y, z - y)
365 #define IN MINE; YOURS; OURS
366 #define OUT YOURS; MINE; OURS
367 #define STR_IN "incoming"
368 #define STR_OUT "outgoing"
370 #define GETHASH(str, dir) do { \
372 HASH_STRING(&h, "tripe-" str); \
374 HASH_DONE(&h, buf); \
375 IF_TRACING(T_KEYSET, { \
376 trace_block(T_CRYPTO, "crypto: " STR_##dir " key " str, \
381 GETHASH("encryption", IN); ks->cin = CIPHER->init(buf, sizeof(buf));
382 GETHASH("integrity", IN); ks->min = MAC->key(buf, sizeof(buf));
383 GETHASH("encryption", OUT); ks->cout = CIPHER->init(buf, sizeof(buf));
384 GETHASH("integrity", OUT); ks->mout = MAC->key(buf, sizeof(buf));
395 T( ks->seq = seq++; )
397 ks->t_exp = now + T_EXP;
399 ks->oseq = ks->iseq = 0;
408 /* --- @ks_tregen@ --- *
410 * Arguments: @keyset *ks@ = pointer to a keyset
412 * Returns: The time at which moves ought to be made to replace this key.
415 time_t ks_tregen(keyset *ks) { return (ks->t_exp - T_EXP + T_REGEN); }
417 /* --- @ks_activate@ --- *
419 * Arguments: @keyset *ks@ = pointer to a keyset
423 * Use: Activates a keyset, so that it can be used for encrypting
427 void ks_activate(keyset *ks)
429 if (ks->f & KSF_LISTEN) {
430 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
431 ks->f &= ~KSF_LISTEN;
435 /* --- @ks_encrypt@ --- *
437 * Arguments: @keyset *ks@ = pointer to a keyset
438 * @unsigned ty@ = message type
439 * @buf *b@ = pointer to input buffer
440 * @buf *bb@ = pointer to output buffer
442 * Returns: Zero if OK, nonzero if the key needs replacing. If the
443 * encryption failed, the output buffer is broken and zero is
446 * Use: Encrypts a block of data using the key. Note that the `key
447 * ought to be replaced' notification is only ever given once
448 * for each key. Also note that this call forces a keyset to be
449 * used even if it's marked as not for data output.
452 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
454 time_t now = time(0);
456 if (!KEYOK(ks, now)) {
460 return (doencrypt(ks, ty, b, bb));
463 /* --- @ks_decrypt@ --- *
465 * Arguments: @keyset *ks@ = pointer to a keyset
466 * @unsigned ty@ = expected type code
467 * @buf *b@ = pointer to an input buffer
468 * @buf *bb@ = pointer to an output buffer
470 * Returns: Zero on success, or nonzero if there was some problem.
472 * Use: Attempts to decrypt a message using a given key. Note that
473 * requesting decryption with a key directly won't clear a
474 * marking that it's not for encryption.
477 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
479 time_t now = time(0);
482 if (!KEYOK(ks, now) ||
483 buf_ensure(bb, BLEN(b)) ||
484 dodecrypt(ks, ty, b, bb, &seq) ||
490 /*----- Keyset list handling ----------------------------------------------*/
492 /* --- @ksl_free@ --- *
494 * Arguments: @keyset **ksroot@ = pointer to keyset list head
498 * Use: Frees (releases references to) all of the keys in a keyset.
501 void ksl_free(keyset **ksroot)
504 for (ks = *ksroot; ks; ks = ksn) {
511 /* --- @ksl_link@ --- *
513 * Arguments: @keyset **ksroot@ = pointer to keyset list head
514 * @keyset *ks@ = pointer to a keyset
518 * Use: Links a keyset into a list. A keyset can only be on one list
519 * at a time. Bad things happen otherwise.
522 void ksl_link(keyset **ksroot, keyset *ks)
524 assert(!(ks->f & KSF_LINK));
531 /* --- @ksl_prune@ --- *
533 * Arguments: @keyset **ksroot@ = pointer to keyset list head
537 * Use: Prunes the keyset list by removing keys which mustn't be used
541 void ksl_prune(keyset **ksroot)
543 time_t now = time(0);
546 keyset *ks = *ksroot;
548 if (ks->t_exp <= now) {
549 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
552 } else if (ks->sz_exp == 0) {
553 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
568 /* --- @ksl_encrypt@ --- *
570 * Arguments: @keyset **ksroot@ = pointer to keyset list head
571 * @unsigned ty@ = message type
572 * @buf *b@ = pointer to input buffer
573 * @buf *bb@ = pointer to output buffer
575 * Returns: Nonzero if a new key is needed.
577 * Use: Encrypts a packet.
580 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
582 time_t now = time(0);
583 keyset *ks = *ksroot;
587 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
591 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
596 return (doencrypt(ks, ty, b, bb));
599 /* --- @ksl_decrypt@ --- *
601 * Arguments: @keyset **ksroot@ = pointer to keyset list head
602 * @unsigned ty@ = expected type code
603 * @buf *b@ = pointer to input buffer
604 * @buf *bb@ = pointer to output buffer
606 * Returns: Nonzero if the packet couldn't be decrypted.
608 * Use: Decrypts a packet.
611 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
613 time_t now = time(0);
617 if (buf_ensure(bb, BLEN(b)))
620 for (ks = *ksroot; ks; ks = ks->next) {
623 if (!dodecrypt(ks, ty, b, bb, &seq)) {
624 if (ks->f & KSF_LISTEN) {
625 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
627 ks->f &= ~KSF_LISTEN;
629 return (dosequence(ks, seq));
632 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
636 /*----- That's all, folks -------------------------------------------------*/