3 * $Id: keyset.c,v 1.7 2003/05/17 11:00:47 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 1.7 2003/05/17 11:00:47 mdw
33 * Don't make scary messages just because one key didn't work on a message:
34 * only be frightened if they all fail. Set initial keyset refcount
37 * Revision 1.6 2003/04/06 10:26:35 mdw
38 * Report peer name on decrypt errors.
40 * Revision 1.5 2001/06/19 22:07:43 mdw
41 * Change the encrypted packet format to be non-malleable.
43 * Revision 1.4 2001/06/16 14:06:40 mdw
44 * Quantify collision probabilities for the stated data volume bounds.
46 * Revision 1.3 2001/02/16 21:39:55 mdw
47 * Major overhaul. Separate functions for manipulating keysets from
48 * functions for manipulating keyset lists. Introduce a concept of
49 * listening-only keys.
51 * Revision 1.2 2001/02/05 19:53:23 mdw
52 * Add sequence number protection.
54 * Revision 1.1 2001/02/03 20:26:37 mdw
59 /*----- Header files ------------------------------------------------------*/
63 /*----- Tunable parameters ------------------------------------------------*/
65 /* --- Note on size limits --- *
67 * For a 64-bit block cipher (e.g., Blowfish), the probability of a collision
68 * occurring after 32 MB is less than %$2^{-21}$%, and the probability of a
69 * collision occurring after 64 MB is less than %$2^{-19}$%.
72 #define T_EXP MIN(60) /* Expiry time for a key */
73 #define T_REGEN MIN(45) /* Regeneration time for a key */
74 #define SZ_EXP MEG(64) /* Expiry data size for a key */
75 #define SZ_REGEN MEG(32) /* Data size threshold for regen */
77 /*----- Handy macros ------------------------------------------------------*/
79 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
81 /*----- Low-level packet encryption and decryption ------------------------*/
83 /* --- Encrypted data format --- *
85 * Let %$p_i$% be the %$i$%-th plaintext message. We first compute
87 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
89 * as the CBC-ciphertext of %$p_i$%, and then
91 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(i, c_i)$%
93 * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
94 * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
95 * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
96 * [Bellare and Namprempre].
98 * This also ensures that, assuming the key is good, we have a secure channel
99 * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
100 * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
101 * then-encrypt scheme and still have a secure channel. However, I like the
102 * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
103 * the Horton Principle [Wagner and Schneier].
106 /* --- @doencrypt@ --- *
108 * Arguments: @keyset *ks@ = pointer to keyset to use
109 * @buf *b@ = pointer to an input buffer
110 * @buf *bb@ = pointer to an output buffer
112 * Returns: Zero if OK, nonzero if a new key is required.
114 * Use: Encrypts a message with the given key. We assume that the
115 * keyset is OK to use.
118 static int doencrypt(keyset *ks, buf *b, buf *bb)
122 const octet *p = BCUR(b);
123 size_t sz = BLEFT(b);
124 octet *qmac, *qseq, *qiv, *qpk;
129 /* --- Allocate the required buffer space --- */
132 if (buf_ensure(bb, MACSZ + SEQSZ + IVSZ + sz))
133 return (0); /* Caution! */
134 qmac = BCUR(bb); qseq = qmac + MACSZ; qiv = qseq + SEQSZ; qpk = qiv + IVSZ;
135 BSTEP(bb, MACSZ + SEQSZ + IVSZ + sz);
137 /* --- Encrypt the packet --- */
139 oseq = ks->oseq++; STORE32(qseq, oseq);
140 rand_get(RAND_GLOBAL, qiv, IVSZ);
141 c->ops->setiv(c, qiv);
142 c->ops->encrypt(c, p, qpk, sz);
143 IF_TRACING(T_KEYSET, {
144 trace(T_KEYSET, "keyset: encrypting packet %lu using keyset %u",
145 (unsigned long)oseq, ks->seq);
146 trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
149 /* --- Now compute the MAC --- */
151 h = ks->mout->ops->init(ks->mout);
152 h->ops->hash(h, qseq, SEQSZ + IVSZ + sz);
153 memcpy(qmac, h->ops->done(h, 0), MACSZ);
155 IF_TRACING(T_KEYSET, {
156 trace_block(T_CRYPTO, "crypto: computed MAC", qmac, MACSZ);
159 /* --- Deduct the packet size from the key's data life --- */
166 if (osz >= SZ_REGEN && nsz < SZ_REGEN) {
167 T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
168 "forcing exchange", ks->seq); )
175 /* --- @dodecrypt@ --- *
177 * Arguments: @keyset *ks@ = pointer to keyset to use
178 * @buf *b@ = pointer to an input buffer
179 * @buf *bb@ = pointer to an output buffer
180 * @uint32 *seq@ = where to store the sequence number
182 * Returns: Zero if OK, nonzero if it failed.
184 * Use: Attempts to decrypt a message with the given key. No other
185 * checking (e.g., sequence number checks) is performed. We
186 * assume that the keyset is OK to use, and that there is
187 * sufficient output buffer space reserved. If the decryption
188 * is successful, the buffer pointer is moved past the decrypted
189 * packet, and the packet's sequence number is stored in @*seq@.
192 static int dodecrypt(keyset *ks, buf *b, buf *bb, uint32 *seq)
194 const octet *pmac, *piv, *pseq, *ppk;
195 size_t psz = BLEFT(b);
199 gcipher *c = ks->cin;
200 size_t ivsz = c->ops->c->blksz;
204 /* --- Break up the packet into its components --- */
206 if (psz < ivsz + 4) {
207 T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
210 sz = psz - IVSZ - SEQSZ - MACSZ;
211 pmac = BCUR(b); pseq = pmac + MACSZ; piv = pseq + SEQSZ; ppk = piv + IVSZ;
213 /* --- Verify the MAC on the packet --- */
215 h = ks->min->ops->init(ks->min);
216 h->ops->hash(h, pseq, SEQSZ + IVSZ + sz);
217 mac = h->ops->done(h, 0);
218 eq = !memcmp(mac, pmac, MACSZ);
219 IF_TRACING(T_KEYSET, {
220 trace(T_KEYSET, "keyset: decrypting using keyset %u", ks->seq);
221 trace_block(T_CRYPTO, "crypto: computed MAC", mac, MACSZ);
225 IF_TRACING(T_KEYSET, {
226 trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
227 trace_block(T_CRYPTO, "crypto: expected MAC", pmac, MACSZ);
232 /* --- Decrypt the packet --- */
234 c->ops->setiv(c, piv);
235 c->ops->decrypt(c, ppk, q, sz);
238 IF_TRACING(T_KEYSET, {
239 trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
240 (unsigned long)LOAD32(pseq));
241 trace_block(T_CRYPTO, "crypto: decrypted packet", q, sz);
247 /* --- @dosequence@ --- *
249 * Arguments: @keyset *ks@ = pointer to a keyset
250 * @uint32 seq@ = a sequence number from a packet
252 * Returns: Zero if the sequence number is OK, nonzero if it's not.
254 * Use: Checks a sequence number. The data in the keyset which keeps
255 * track of valid sequence numbers is updated if the sequence
256 * number given is good. It's assumed that the sequence number
257 * has already been checked for authenticity.
260 static int dosequence(keyset *ks, uint32 seq)
265 if (seq < ks->iseq) {
266 a_warn("received packet has old sequence number (possible replay)");
269 if (seq >= ks->iseq + KS_SEQWINSZ) {
270 n = seq - (ks->iseq + KS_SEQWINSZ - 1);
277 seqbit = 1 << (seq - ks->iseq);
278 if (ks->iwin & seqbit) {
279 a_warn("received packet repeats old sequence number");
286 /*----- Operations on a single keyset -------------------------------------*/
288 /* --- @ks_drop@ --- *
290 * Arguments: @keyset *ks@ = pointer to a keyset
294 * Use: Decrements a keyset's reference counter. If the counter hits
295 * zero, the keyset is freed.
298 void ks_drop(keyset *ks)
302 ks->cin->ops->destroy(ks->cin);
303 ks->cout->ops->destroy(ks->cout);
304 ks->min->ops->destroy(ks->min);
305 ks->mout->ops->destroy(ks->mout);
309 /* --- @ks_gen@ --- *
311 * Arguments: @const void *k@ = pointer to key material
312 * @size_t x, y, z@ = offsets into key material (see below)
313 * @peer *p@ = pointer to peer information
315 * Returns: A pointer to the new keyset.
317 * Use: Derives a new keyset from the given key material. The
318 * offsets @x@, @y@ and @z@ separate the key material into three
319 * parts. Between the @k@ and @k + x@ is `my' contribution to
320 * the key material; between @k + x@ and @k + y@ is `your'
321 * contribution; and between @k + y@ and @k + z@ is a shared
322 * value we made together. These are used to construct two
323 * pairs of symmetric keys. Each pair consists of an encryption
324 * key and a message authentication key. One pair is used for
325 * outgoing messages, the other for incoming messages.
327 * The new key is marked so that it won't be selected for output
328 * by @ksl_encrypt@. You can still encrypt data with it by
329 * calling @ks_encrypt@ directly.
332 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
336 keyset *ks = CREATE(keyset);
337 time_t now = time(0);
339 T( static unsigned seq = 0; )
341 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
343 /* --- Construct the various keys --- *
345 * This is done with macros, because it's quite tedious.
348 #define MINE HASH(&h, pp, x)
349 #define YOURS HASH(&h, pp + x, y - x)
350 #define OURS HASH(&h, pp + y, z - y)
352 #define IN MINE; YOURS; OURS
353 #define OUT YOURS; MINE; OURS
354 #define STR_IN "incoming"
355 #define STR_OUT "outgoing"
357 #define GETHASH(str, dir) do { \
359 HASH_STRING(&h, "tripe-" str); \
361 HASH_DONE(&h, buf); \
362 IF_TRACING(T_KEYSET, { \
363 trace_block(T_CRYPTO, "crypto: " STR_##dir " key " str, \
368 GETHASH("encryption", IN); ks->cin = CIPHER->init(buf, sizeof(buf));
369 GETHASH("integrity", IN); ks->min = MAC->key(buf, sizeof(buf));
370 GETHASH("encryption", OUT); ks->cout = CIPHER->init(buf, sizeof(buf));
371 GETHASH("integrity", OUT); ks->mout = MAC->key(buf, sizeof(buf));
382 T( ks->seq = seq++; )
384 ks->t_exp = now + T_EXP;
386 ks->oseq = ks->iseq = 0;
395 /* --- @ks_tregen@ --- *
397 * Arguments: @keyset *ks@ = pointer to a keyset
399 * Returns: The time at which moves ought to be made to replace this key.
402 time_t ks_tregen(keyset *ks) { return (ks->t_exp - T_EXP + T_REGEN); }
404 /* --- @ks_activate@ --- *
406 * Arguments: @keyset *ks@ = pointer to a keyset
410 * Use: Activates a keyset, so that it can be used for encrypting
414 void ks_activate(keyset *ks)
416 if (ks->f & KSF_LISTEN) {
417 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
418 ks->f &= ~KSF_LISTEN;
422 /* --- @ks_encrypt@ --- *
424 * Arguments: @keyset *ks@ = pointer to a keyset
425 * @buf *b@ = pointer to input buffer
426 * @buf *bb@ = pointer to output buffer
428 * Returns: Zero if OK, nonzero if the key needs replacing. If the
429 * encryption failed, the output buffer is broken and zero is
432 * Use: Encrypts a block of data using the key. Note that the `key
433 * ought to be replaced' notification is only ever given once
434 * for each key. Also note that this call forces a keyset to be
435 * used even if it's marked as not for data output.
438 int ks_encrypt(keyset *ks, buf *b, buf *bb)
440 time_t now = time(0);
442 if (!KEYOK(ks, now)) {
446 return (doencrypt(ks, b, bb));
449 /* --- @ks_decrypt@ --- *
451 * Arguments: @keyset *ks@ = pointer to a keyset
452 * @buf *b@ = pointer to an input buffer
453 * @buf *bb@ = pointer to an output buffer
455 * Returns: Zero on success, or nonzero if there was some problem.
457 * Use: Attempts to decrypt a message using a given key. Note that
458 * requesting decryption with a key directly won't clear a
459 * marking that it's not for encryption.
462 int ks_decrypt(keyset *ks, buf *b, buf *bb)
464 time_t now = time(0);
467 if (!KEYOK(ks, now) ||
468 buf_ensure(bb, BLEN(b)) ||
469 dodecrypt(ks, b, bb, &seq) ||
475 /*----- Keyset list handling ----------------------------------------------*/
477 /* --- @ksl_free@ --- *
479 * Arguments: @keyset **ksroot@ = pointer to keyset list head
483 * Use: Frees (releases references to) all of the keys in a keyset.
486 void ksl_free(keyset **ksroot)
489 for (ks = *ksroot; ks; ks = ksn) {
496 /* --- @ksl_link@ --- *
498 * Arguments: @keyset **ksroot@ = pointer to keyset list head
499 * @keyset *ks@ = pointer to a keyset
503 * Use: Links a keyset into a list. A keyset can only be on one list
504 * at a time. Bad things happen otherwise.
507 void ksl_link(keyset **ksroot, keyset *ks)
509 assert(!(ks->f & KSF_LINK));
516 /* --- @ksl_prune@ --- *
518 * Arguments: @keyset **ksroot@ = pointer to keyset list head
522 * Use: Prunes the keyset list by removing keys which mustn't be used
526 void ksl_prune(keyset **ksroot)
528 time_t now = time(0);
531 keyset *ks = *ksroot;
533 if (ks->t_exp <= now) {
534 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
537 } else if (ks->sz_exp == 0) {
538 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
553 /* --- @ksl_encrypt@ --- *
555 * Arguments: @keyset **ksroot@ = pointer to keyset list head
556 * @buf *b@ = pointer to input buffer
557 * @buf *bb@ = pointer to output buffer
559 * Returns: Nonzero if a new key is needed.
561 * Use: Encrypts a packet.
564 int ksl_encrypt(keyset **ksroot, buf *b, buf *bb)
566 time_t now = time(0);
567 keyset *ks = *ksroot;
571 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
575 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
580 return (doencrypt(ks, b, bb));
583 /* --- @ksl_decrypt@ --- *
585 * Arguments: @keyset **ksroot@ = pointer to keyset list head
586 * @buf *b@ = pointer to input buffer
587 * @buf *bb@ = pointer to output buffer
589 * Returns: Nonzero if the packet couldn't be decrypted.
591 * Use: Decrypts a packet.
594 int ksl_decrypt(keyset **ksroot, buf *b, buf *bb)
596 time_t now = time(0);
600 if (buf_ensure(bb, BLEN(b)))
603 for (ks = *ksroot; ks; ks = ks->next) {
606 if (!dodecrypt(ks, b, bb, &seq)) {
607 if (ks->f & KSF_LISTEN) {
608 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
610 ks->f &= ~KSF_LISTEN;
612 return (dosequence(ks, seq));
615 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
619 /*----- That's all, folks -------------------------------------------------*/