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[tripe] / keyset.c
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410c8acf 1/* -*-c-*-
2 *
3cdc3f3a 3 * $Id$
410c8acf 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
410c8acf 29/*----- Header files ------------------------------------------------------*/
30
31#include "tripe.h"
32
33/*----- Tunable parameters ------------------------------------------------*/
34
d132c651 35/* --- Note on size limits --- *
36 *
37 * For a 64-bit block cipher (e.g., Blowfish), the probability of a collision
38 * occurring after 32 MB is less than %$2^{-21}$%, and the probability of a
b5c45da1 39 * collision occurring after 64 MB is less than %$2^{-19}$%. These could be
40 * adjusted dependent on the encryption scheme, but it's too much pain.
d132c651 41 */
42
426c0bc6 43#define T_EXP MIN(60) /* Expiry time for a key */
44#define T_REGEN MIN(45) /* Regeneration time for a key */
45#define SZ_EXP MEG(64) /* Expiry data size for a key */
46#define SZ_REGEN MEG(32) /* Data size threshold for regen */
410c8acf 47
48/*----- Handy macros ------------------------------------------------------*/
49
50#define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
51
b5c45da1 52#define SEQSZ 4 /* Size of sequence number packet */
53
426c0bc6 54/*----- Low-level packet encryption and decryption ------------------------*/
410c8acf 55
59d670e7 56/* --- Encrypted data format --- *
57 *
7ed14135 58 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
59 * compute
59d670e7 60 *
61 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
62 *
63 * as the CBC-ciphertext of %$p_i$%, and then
64 *
7ed14135 65 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
59d670e7 66 *
67 * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
68 * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
69 * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
70 * [Bellare and Namprempre].
71 *
72 * This also ensures that, assuming the key is good, we have a secure channel
73 * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
74 * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
75 * then-encrypt scheme and still have a secure channel. However, I like the
76 * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
77 * the Horton Principle [Wagner and Schneier].
78 */
79
426c0bc6 80/* --- @doencrypt@ --- *
410c8acf 81 *
426c0bc6 82 * Arguments: @keyset *ks@ = pointer to keyset to use
7ed14135 83 * @unsigned ty@ = type of message this is
426c0bc6 84 * @buf *b@ = pointer to an input buffer
85 * @buf *bb@ = pointer to an output buffer
410c8acf 86 *
426c0bc6 87 * Returns: Zero if OK, nonzero if a new key is required.
410c8acf 88 *
426c0bc6 89 * Use: Encrypts a message with the given key. We assume that the
90 * keyset is OK to use.
410c8acf 91 */
92
7ed14135 93static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
410c8acf 94{
426c0bc6 95 ghash *h;
b5c45da1 96 gcipher *c = ks->cout;
426c0bc6 97 const octet *p = BCUR(b);
98 size_t sz = BLEFT(b);
59d670e7 99 octet *qmac, *qseq, *qiv, *qpk;
426c0bc6 100 uint32 oseq;
b5c45da1 101 size_t ivsz = GC_CLASS(c)->blksz;
102 size_t tagsz = ks->tagsz;
426c0bc6 103 size_t osz, nsz;
7ed14135 104 octet t[4];
426c0bc6 105 int rc = 0;
106
107 /* --- Allocate the required buffer space --- */
108
b5c45da1 109 if (buf_ensure(bb, tagsz + SEQSZ + ivsz + sz))
426c0bc6 110 return (0); /* Caution! */
b5c45da1 111 qmac = BCUR(bb); qseq = qmac + tagsz; qiv = qseq + SEQSZ; qpk = qiv + ivsz;
112 BSTEP(bb, tagsz + SEQSZ + ivsz + sz);
7ed14135 113 STORE32(t, ty);
426c0bc6 114
426c0bc6 115 oseq = ks->oseq++; STORE32(qseq, oseq);
426c0bc6 116 IF_TRACING(T_KEYSET, {
117 trace(T_KEYSET, "keyset: encrypting packet %lu using keyset %u",
118 (unsigned long)oseq, ks->seq);
b5c45da1 119 trace_block(T_CRYPTO, "crypto: plaintext packet", p, sz);
426c0bc6 120 })
59d670e7 121
b5c45da1 122 /* --- Encrypt the packet --- */
59d670e7 123
b5c45da1 124 if (ivsz) {
125 rand_get(RAND_GLOBAL, qiv, ivsz);
126 GC_SETIV(c, qiv);
127 IF_TRACING(T_KEYSET, {
128 trace_block(T_CRYPTO, "crypto: initialization vector", qiv, ivsz);
129 })
130 }
131 GC_ENCRYPT(c, p, qpk, sz);
426c0bc6 132 IF_TRACING(T_KEYSET, {
b5c45da1 133 trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
426c0bc6 134 })
135
b5c45da1 136 /* --- Now compute the MAC --- */
137
138 if (tagsz) {
139 h = GM_INIT(ks->mout);
140 GH_HASH(h, t, sizeof(t));
141 GH_HASH(h, qseq, SEQSZ + ivsz + sz);
142 memcpy(qmac, GH_DONE(h, 0), tagsz);
143 GH_DESTROY(h);
144 IF_TRACING(T_KEYSET, {
145 trace_block(T_CRYPTO, "crypto: computed MAC", qmac, tagsz);
146 })
147 }
148
426c0bc6 149 /* --- Deduct the packet size from the key's data life --- */
150
151 osz = ks->sz_exp;
152 if (osz > sz)
153 nsz = osz - sz;
154 else
155 nsz = 0;
156 if (osz >= SZ_REGEN && nsz < SZ_REGEN) {
157 T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
158 "forcing exchange", ks->seq); )
159 rc = -1;
160 }
161 ks->sz_exp = nsz;
162 return (rc);
410c8acf 163}
164
426c0bc6 165/* --- @dodecrypt@ --- *
410c8acf 166 *
426c0bc6 167 * Arguments: @keyset *ks@ = pointer to keyset to use
7ed14135 168 * @unsigned ty@ = expected type code
426c0bc6 169 * @buf *b@ = pointer to an input buffer
170 * @buf *bb@ = pointer to an output buffer
171 * @uint32 *seq@ = where to store the sequence number
410c8acf 172 *
426c0bc6 173 * Returns: Zero if OK, nonzero if it failed.
410c8acf 174 *
426c0bc6 175 * Use: Attempts to decrypt a message with the given key. No other
176 * checking (e.g., sequence number checks) is performed. We
177 * assume that the keyset is OK to use, and that there is
178 * sufficient output buffer space reserved. If the decryption
179 * is successful, the buffer pointer is moved past the decrypted
180 * packet, and the packet's sequence number is stored in @*seq@.
410c8acf 181 */
182
7ed14135 183static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
410c8acf 184{
59d670e7 185 const octet *pmac, *piv, *pseq, *ppk;
426c0bc6 186 size_t psz = BLEFT(b);
187 size_t sz;
188 octet *q = BCUR(bb);
189 ghash *h;
190 gcipher *c = ks->cin;
b5c45da1 191 size_t ivsz = GC_CLASS(c)->blksz;
192 size_t tagsz = ks->tagsz;
426c0bc6 193 octet *mac;
194 int eq;
7ed14135 195 octet t[4];
426c0bc6 196
197 /* --- Break up the packet into its components --- */
198
b5c45da1 199 if (psz < ivsz + SEQSZ + tagsz) {
426c0bc6 200 T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
201 return (-1);
410c8acf 202 }
b5c45da1 203 sz = psz - ivsz - SEQSZ - tagsz;
204 pmac = BCUR(b); pseq = pmac + tagsz; piv = pseq + SEQSZ; ppk = piv + ivsz;
7ed14135 205 STORE32(t, ty);
426c0bc6 206
426c0bc6 207 IF_TRACING(T_KEYSET, {
208 trace(T_KEYSET, "keyset: decrypting using keyset %u", ks->seq);
b5c45da1 209 trace_block(T_CRYPTO, "crypto: ciphertext packet", ppk, sz);
426c0bc6 210 })
b5c45da1 211
212 /* --- Verify the MAC on the packet --- */
213
214 if (tagsz) {
215 h = GM_INIT(ks->min);
216 GH_HASH(h, t, sizeof(t));
217 GH_HASH(h, pseq, SEQSZ + ivsz + sz);
218 mac = GH_DONE(h, 0);
219 eq = !memcmp(mac, pmac, tagsz);
426c0bc6 220 IF_TRACING(T_KEYSET, {
b5c45da1 221 trace_block(T_CRYPTO, "crypto: computed MAC", mac, tagsz);
426c0bc6 222 })
b5c45da1 223 GH_DESTROY(h);
224 if (!eq) {
225 IF_TRACING(T_KEYSET, {
226 trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
227 trace_block(T_CRYPTO, "crypto: expected MAC", pmac, tagsz);
228 })
229 return (-1);
230 }
426c0bc6 231 }
59d670e7 232
233 /* --- Decrypt the packet --- */
234
b5c45da1 235 if (ivsz) {
236 GC_SETIV(c, piv);
237 IF_TRACING(T_KEYSET, {
238 trace_block(T_CRYPTO, "crypto: initialization vector", piv, ivsz);
239 })
240 }
241 GC_DECRYPT(c, ppk, q, sz);
426c0bc6 242 if (seq)
243 *seq = LOAD32(pseq);
244 IF_TRACING(T_KEYSET, {
245 trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
246 (unsigned long)LOAD32(pseq));
247 trace_block(T_CRYPTO, "crypto: decrypted packet", q, sz);
248 })
249 BSTEP(bb, sz);
250 return (0);
410c8acf 251}
252
426c0bc6 253/*----- Operations on a single keyset -------------------------------------*/
254
255/* --- @ks_drop@ --- *
256 *
257 * Arguments: @keyset *ks@ = pointer to a keyset
258 *
259 * Returns: ---
260 *
261 * Use: Decrements a keyset's reference counter. If the counter hits
262 * zero, the keyset is freed.
263 */
264
265void ks_drop(keyset *ks)
266{
267 if (--ks->ref)
268 return;
b5c45da1 269 GC_DESTROY(ks->cin);
270 GC_DESTROY(ks->cout);
271 GM_DESTROY(ks->min);
272 GM_DESTROY(ks->mout);
426c0bc6 273 DESTROY(ks);
410c8acf 274}
275
276/* --- @ks_gen@ --- *
277 *
426c0bc6 278 * Arguments: @const void *k@ = pointer to key material
279 * @size_t x, y, z@ = offsets into key material (see below)
9466fafa 280 * @peer *p@ = pointer to peer information
410c8acf 281 *
426c0bc6 282 * Returns: A pointer to the new keyset.
410c8acf 283 *
426c0bc6 284 * Use: Derives a new keyset from the given key material. The
285 * offsets @x@, @y@ and @z@ separate the key material into three
286 * parts. Between the @k@ and @k + x@ is `my' contribution to
287 * the key material; between @k + x@ and @k + y@ is `your'
288 * contribution; and between @k + y@ and @k + z@ is a shared
289 * value we made together. These are used to construct two
290 * pairs of symmetric keys. Each pair consists of an encryption
291 * key and a message authentication key. One pair is used for
292 * outgoing messages, the other for incoming messages.
293 *
294 * The new key is marked so that it won't be selected for output
295 * by @ksl_encrypt@. You can still encrypt data with it by
296 * calling @ks_encrypt@ directly.
410c8acf 297 */
298
9466fafa 299keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
410c8acf 300{
b5c45da1 301 ghash *h;
302 const octet *hh;
410c8acf 303 keyset *ks = CREATE(keyset);
304 time_t now = time(0);
9466fafa 305 const octet *pp = k;
410c8acf 306 T( static unsigned seq = 0; )
307
308 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
309
426c0bc6 310 /* --- Construct the various keys --- *
311 *
312 * This is done with macros, because it's quite tedious.
313 */
314
b5c45da1 315#define MINE GH_HASH(h, pp, x)
316#define YOURS GH_HASH(h, pp + x, y - x)
317#define OURS GH_HASH(h, pp + y, z - y)
318
319#define HASH_in MINE; YOURS; OURS
320#define HASH_out YOURS; MINE; OURS
321#define INIT_c(k) GC_INIT(algs.c, (k), algs.cksz)
322#define INIT_m(k) GM_KEY(algs.m, (k), algs.mksz)
323#define STR_c "encryption"
324#define STR_m "integrity"
325#define STR_in "incoming"
326#define STR_out "outgoing"
327
328#define SETKEY(a, dir) do { \
329 h = GH_INIT(algs.h); \
330 HASH_STRING(h, "tripe-" STR_##a); \
331 HASH_##dir; \
332 hh = GH_DONE(h, 0); \
410c8acf 333 IF_TRACING(T_KEYSET, { \
b5c45da1 334 trace_block(T_CRYPTO, "crypto: " STR_##dir " key " STR_##a, \
335 hh, algs.a##ksz); \
410c8acf 336 }) \
b5c45da1 337 ks->a##dir = INIT_##a(hh); \
338 GH_DESTROY(h); \
410c8acf 339} while (0)
340
b5c45da1 341 SETKEY(c, in); SETKEY(c, out);
342 SETKEY(m, in); SETKEY(m, out);
426c0bc6 343
344#undef MINE
345#undef YOURS
346#undef OURS
b5c45da1 347#undef STR_c
348#undef STR_m
349#undef STR_in
350#undef STR_out
351#undef INIT_c
352#undef INIT_m
353#undef HASH_in
354#undef HASH_out
355#undef SETKEY
410c8acf 356
357 T( ks->seq = seq++; )
e945d6e4 358 ks->ref = 1;
426c0bc6 359 ks->t_exp = now + T_EXP;
360 ks->sz_exp = SZ_EXP;
37941236 361 ks->oseq = 0;
362 seq_reset(&ks->iseq);
426c0bc6 363 ks->next = 0;
9466fafa 364 ks->p = p;
426c0bc6 365 ks->f = KSF_LISTEN;
b5c45da1 366 ks->tagsz = algs.tagsz;
426c0bc6 367 return (ks);
368}
369
370/* --- @ks_tregen@ --- *
371 *
372 * Arguments: @keyset *ks@ = pointer to a keyset
373 *
374 * Returns: The time at which moves ought to be made to replace this key.
375 */
376
377time_t ks_tregen(keyset *ks) { return (ks->t_exp - T_EXP + T_REGEN); }
378
379/* --- @ks_activate@ --- *
380 *
381 * Arguments: @keyset *ks@ = pointer to a keyset
382 *
383 * Returns: ---
384 *
385 * Use: Activates a keyset, so that it can be used for encrypting
386 * outgoing messages.
387 */
388
389void ks_activate(keyset *ks)
390{
391 if (ks->f & KSF_LISTEN) {
392 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
393 ks->f &= ~KSF_LISTEN;
394 }
410c8acf 395}
396
397/* --- @ks_encrypt@ --- *
398 *
426c0bc6 399 * Arguments: @keyset *ks@ = pointer to a keyset
7ed14135 400 * @unsigned ty@ = message type
426c0bc6 401 * @buf *b@ = pointer to input buffer
402 * @buf *bb@ = pointer to output buffer
403 *
404 * Returns: Zero if OK, nonzero if the key needs replacing. If the
405 * encryption failed, the output buffer is broken and zero is
406 * returned.
407 *
408 * Use: Encrypts a block of data using the key. Note that the `key
409 * ought to be replaced' notification is only ever given once
410 * for each key. Also note that this call forces a keyset to be
411 * used even if it's marked as not for data output.
412 */
413
7ed14135 414int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
426c0bc6 415{
416 time_t now = time(0);
417
418 if (!KEYOK(ks, now)) {
419 buf_break(bb);
420 return (0);
421 }
7ed14135 422 return (doencrypt(ks, ty, b, bb));
426c0bc6 423}
424
425/* --- @ks_decrypt@ --- *
426 *
427 * Arguments: @keyset *ks@ = pointer to a keyset
7ed14135 428 * @unsigned ty@ = expected type code
426c0bc6 429 * @buf *b@ = pointer to an input buffer
430 * @buf *bb@ = pointer to an output buffer
431 *
432 * Returns: Zero on success, or nonzero if there was some problem.
433 *
434 * Use: Attempts to decrypt a message using a given key. Note that
435 * requesting decryption with a key directly won't clear a
436 * marking that it's not for encryption.
437 */
438
7ed14135 439int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
426c0bc6 440{
441 time_t now = time(0);
442 uint32 seq;
443
444 if (!KEYOK(ks, now) ||
445 buf_ensure(bb, BLEN(b)) ||
7ed14135 446 dodecrypt(ks, ty, b, bb, &seq) ||
f43df819 447 seq_check(&ks->iseq, seq, "SYMM"))
426c0bc6 448 return (-1);
449 return (0);
450}
451
452/*----- Keyset list handling ----------------------------------------------*/
453
454/* --- @ksl_free@ --- *
455 *
456 * Arguments: @keyset **ksroot@ = pointer to keyset list head
457 *
458 * Returns: ---
459 *
460 * Use: Frees (releases references to) all of the keys in a keyset.
461 */
462
463void ksl_free(keyset **ksroot)
464{
465 keyset *ks, *ksn;
466 for (ks = *ksroot; ks; ks = ksn) {
467 ksn = ks->next;
468 ks->f &= ~KSF_LINK;
469 ks_drop(ks);
470 }
471}
472
473/* --- @ksl_link@ --- *
474 *
475 * Arguments: @keyset **ksroot@ = pointer to keyset list head
476 * @keyset *ks@ = pointer to a keyset
477 *
478 * Returns: ---
479 *
480 * Use: Links a keyset into a list. A keyset can only be on one list
481 * at a time. Bad things happen otherwise.
482 */
483
484void ksl_link(keyset **ksroot, keyset *ks)
485{
486 assert(!(ks->f & KSF_LINK));
487 ks->next = *ksroot;
488 *ksroot = ks;
489 ks->f |= KSF_LINK;
490 ks->ref++;
491}
492
493/* --- @ksl_prune@ --- *
494 *
495 * Arguments: @keyset **ksroot@ = pointer to keyset list head
496 *
497 * Returns: ---
498 *
499 * Use: Prunes the keyset list by removing keys which mustn't be used
500 * any more.
501 */
502
503void ksl_prune(keyset **ksroot)
504{
505 time_t now = time(0);
506
507 while (*ksroot) {
508 keyset *ks = *ksroot;
509
510 if (ks->t_exp <= now) {
511 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
512 ks->seq); )
513 goto kill;
514 } else if (ks->sz_exp == 0) {
515 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
516 ks->seq); )
517 goto kill;
518 } else {
519 ksroot = &ks->next;
520 continue;
521 }
522
523 kill:
524 *ksroot = ks->next;
525 ks->f &= ~KSF_LINK;
526 ks_drop(ks);
527 }
528}
529
530/* --- @ksl_encrypt@ --- *
531 *
410c8acf 532 * Arguments: @keyset **ksroot@ = pointer to keyset list head
7ed14135 533 * @unsigned ty@ = message type
410c8acf 534 * @buf *b@ = pointer to input buffer
535 * @buf *bb@ = pointer to output buffer
536 *
537 * Returns: Nonzero if a new key is needed.
538 *
539 * Use: Encrypts a packet.
540 */
541
7ed14135 542int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
410c8acf 543{
544 time_t now = time(0);
426c0bc6 545 keyset *ks = *ksroot;
410c8acf 546
410c8acf 547 for (;;) {
548 if (!ks) {
426c0bc6 549 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
410c8acf 550 buf_break(bb);
551 return (-1);
552 }
426c0bc6 553 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
410c8acf 554 break;
555 ks = ks->next;
556 }
557
7ed14135 558 return (doencrypt(ks, ty, b, bb));
410c8acf 559}
560
426c0bc6 561/* --- @ksl_decrypt@ --- *
410c8acf 562 *
563 * Arguments: @keyset **ksroot@ = pointer to keyset list head
7ed14135 564 * @unsigned ty@ = expected type code
410c8acf 565 * @buf *b@ = pointer to input buffer
566 * @buf *bb@ = pointer to output buffer
567 *
568 * Returns: Nonzero if the packet couldn't be decrypted.
569 *
570 * Use: Decrypts a packet.
571 */
572
7ed14135 573int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
410c8acf 574{
575 time_t now = time(0);
410c8acf 576 keyset *ks;
426c0bc6 577 uint32 seq;
410c8acf 578
426c0bc6 579 if (buf_ensure(bb, BLEN(b)))
410c8acf 580 return (-1);
09585a65 581
410c8acf 582 for (ks = *ksroot; ks; ks = ks->next) {
410c8acf 583 if (!KEYOK(ks, now))
584 continue;
7ed14135 585 if (!dodecrypt(ks, ty, b, bb, &seq)) {
426c0bc6 586 if (ks->f & KSF_LISTEN) {
587 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
588 ks->seq); )
589 ks->f &= ~KSF_LISTEN;
590 }
f43df819 591 return (seq_check(&ks->iseq, seq, "SYMM"));
410c8acf 592 }
410c8acf 593 }
e945d6e4 594 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
410c8acf 595 return (-1);
596}
597
598/*----- That's all, folks -------------------------------------------------*/