server/admin.c: Fix `=' vs `==' error in assertion.
[tripe] / server / keyset.c
1 /* -*-c-*-
2 *
3 * Handling of symmetric keysets
4 *
5 * (c) 2001 Straylight/Edgeware
6 */
7
8 /*----- Licensing notice --------------------------------------------------*
9 *
10 * This file is part of Trivial IP Encryption (TrIPE).
11 *
12 * TrIPE is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License as published by
14 * the Free Software Foundation; either version 2 of the License, or
15 * (at your option) any later version.
16 *
17 * TrIPE is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU General Public License for more details.
21 *
22 * You should have received a copy of the GNU General Public License
23 * along with TrIPE; if not, write to the Free Software Foundation,
24 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
25 */
26
27 /*----- Header files ------------------------------------------------------*/
28
29 #include "tripe.h"
30
31 /*----- Handy macros ------------------------------------------------------*/
32
33 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
34
35 /*----- Low-level packet encryption and decryption ------------------------*/
36
37 /* --- Encrypted data format --- *
38 *
39 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
40 * compute
41 *
42 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
43 *
44 * as the CBC-ciphertext of %$p_i$%, and then
45 *
46 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
47 *
48 * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
49 * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
50 * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
51 * [Bellare and Namprempre].
52 *
53 * This also ensures that, assuming the key is good, we have a secure channel
54 * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
55 * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
56 * then-encrypt scheme and still have a secure channel. However, I like the
57 * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
58 * the Horton Principle [Wagner and Schneier].
59 */
60
61 /* --- @doencrypt@ --- *
62 *
63 * Arguments: @keyset *ks@ = pointer to keyset to use
64 * @unsigned ty@ = type of message this is
65 * @buf *b@ = pointer to an input buffer
66 * @buf *bb@ = pointer to an output buffer
67 *
68 * Returns: Zero if OK; @KSERR_REGEN@ if it's time to generate new keys.
69 * Also returns zero if there was insufficient buffer space, but
70 * the buffer is broken in this case.
71 *
72 * Use: Encrypts a message with the given key. We assume that the
73 * keyset is OK to use.
74 */
75
76 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
77 {
78 int rc;
79 size_t sz = BLEFT(b);
80 size_t osz, nsz;
81
82 /* --- Initial tracing --- */
83
84 IF_TRACING(T_KEYSET, {
85 trace(T_KEYSET,
86 "keyset: encrypting packet %lu (type %u) using keyset %u",
87 (unsigned long)ks->oseq, ty, ks->seq);
88 trace_block(T_CRYPTO, "crypto: plaintext packet", BCUR(b), sz);
89 })
90
91 /* --- Apply the bulk-crypto transformation --- */
92
93 rc = ks->bulk->ops->encrypt(ks->bulk, ty, b, bb, ks->oseq);
94 if (rc || !BOK(bb)) return (rc);
95 ks->oseq++;
96
97 /* --- Do the necessary accounting for data volume --- */
98
99 osz = ks->sz_exp;
100 nsz = osz > sz ? osz - sz : 0;
101 if (osz >= ks->sz_regen && ks->sz_regen > nsz) {
102 T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
103 "forcing exchange", ks->seq); )
104 rc = KSERR_REGEN;
105 }
106 ks->sz_exp = nsz;
107
108 /* --- We're done --- */
109
110 return (rc);
111 }
112
113 /* --- @dodecrypt@ --- *
114 *
115 * Arguments: @keyset *ks@ = pointer to keyset to use
116 * @unsigned ty@ = expected type code
117 * @buf *b@ = pointer to an input buffer
118 * @buf *bb@ = pointer to an output buffer
119 * @uint32 *seq@ = where to store the sequence number
120 *
121 * Returns: Zero on success; @KSERR_DECRYPT@ on failure.
122 *
123 * Use: Attempts to decrypt a message with the given key. No other
124 * checking (e.g., sequence number checks) is performed. We
125 * assume that the keyset is OK to use, and that there is
126 * sufficient output buffer space reserved. If the decryption
127 * is successful, the buffer pointer is moved past the decrypted
128 * packet, and the packet's sequence number is stored in @*seq@.
129 */
130
131 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
132 {
133 const octet *q = BCUR(bb);
134 int rc;
135
136 IF_TRACING(T_KEYSET, {
137 trace(T_KEYSET,
138 "keyset: try decrypting packet (type %u) using keyset %u",
139 ty, ks->seq);
140 trace_block(T_CRYPTO, "crypto: ciphertext packet", BCUR(b), BLEFT(b));
141 })
142
143 rc = ks->bulk->ops->decrypt(ks->bulk, ty, b, bb, seq);
144 if (rc) return (rc);
145
146 IF_TRACING(T_KEYSET, {
147 trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
148 (unsigned long)*seq);
149 trace_block(T_CRYPTO, "crypto: decrypted packet", q, BCUR(bb) - q);
150 })
151 return (0);
152 }
153
154 /*----- Operations on a single keyset -------------------------------------*/
155
156 /* --- @ks_drop@ --- *
157 *
158 * Arguments: @keyset *ks@ = pointer to a keyset
159 *
160 * Returns: ---
161 *
162 * Use: Decrements a keyset's reference counter. If the counter hits
163 * zero, the keyset is freed.
164 */
165
166 void ks_drop(keyset *ks)
167 {
168 if (--ks->ref) return;
169 ks->bulk->ops->freectx(ks->bulk);
170 DESTROY(ks);
171 }
172
173 /* --- @ks_derivekey@ --- *
174 *
175 * Arguments: @octet *k@ = pointer to an output buffer of at least
176 * @MAXHASHSZ@ bytes
177 * @size_t ksz@ = actual size wanted (for tracing)
178 * @const struct rawkey *rk@ = a raw key, as passed into
179 * @genkeys@
180 * @int dir@ = direction for the key (@DIR_IN@ or @DIR_OUT@)
181 * @const char *what@ = label for the key (input to derivation)
182 *
183 * Returns: ---
184 *
185 * Use: Derives a session key, for use on incoming or outgoing data.
186 * This function is part of a private protocol between @ks_gen@
187 * and the bulk crypto transform @genkeys@ operation.
188 */
189
190 struct rawkey {
191 const gchash *hc;
192 const octet *k;
193 size_t x, y, z;
194 };
195
196 void ks_derivekey(octet *k, size_t ksz, const struct rawkey *rk,
197 int dir, const char *what)
198 {
199 const gchash *hc = rk->hc;
200 ghash *h;
201
202 assert(ksz <= hc->hashsz);
203 assert(hc->hashsz <= MAXHASHSZ);
204 h = GH_INIT(hc);
205 GH_HASH(h, "tripe-", 6); GH_HASH(h, what, strlen(what) + 1);
206 switch (dir) {
207 case DIR_IN:
208 GH_HASH(h, rk->k, rk->x);
209 GH_HASH(h, rk->k + rk->x, rk->y - rk->x);
210 break;
211 case DIR_OUT:
212 GH_HASH(h, rk->k + rk->x, rk->y - rk->x);
213 GH_HASH(h, rk->k, rk->x);
214 break;
215 default:
216 abort();
217 }
218 GH_HASH(h, rk->k + rk->y, rk->z - rk->y);
219 GH_DONE(h, k);
220 GH_DESTROY(h);
221 IF_TRACING(T_KEYSET, { IF_TRACING(T_CRYPTO, {
222 char _buf[32];
223 sprintf(_buf, "crypto: %s key %s", dir ? "incoming" : "outgoing", what);
224 trace_block(T_CRYPTO, _buf, k, ksz);
225 }) })
226 }
227
228 /* --- @ks_gen@ --- *
229 *
230 * Arguments: @const void *k@ = pointer to key material
231 * @size_t x, y, z@ = offsets into key material (see below)
232 * @peer *p@ = pointer to peer information
233 *
234 * Returns: A pointer to the new keyset.
235 *
236 * Use: Derives a new keyset from the given key material. The
237 * offsets @x@, @y@ and @z@ separate the key material into three
238 * parts. Between the @k@ and @k + x@ is `my' contribution to
239 * the key material; between @k + x@ and @k + y@ is `your'
240 * contribution; and between @k + y@ and @k + z@ is a shared
241 * value we made together. These are used to construct two
242 * pairs of symmetric keys. Each pair consists of an encryption
243 * key and a message authentication key. One pair is used for
244 * outgoing messages, the other for incoming messages.
245 *
246 * The new key is marked so that it won't be selected for output
247 * by @ksl_encrypt@. You can still encrypt data with it by
248 * calling @ks_encrypt@ directly.
249 */
250
251 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
252 {
253 keyset *ks = CREATE(keyset);
254 time_t now = time(0);
255 const algswitch *algs = &p->kx.kpriv->algs;
256 struct rawkey rk;
257 T( static unsigned seq = 0; )
258
259 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
260
261 rk.hc = algs->h; rk.k = k; rk.x = x; rk.y = y; rk.z = z;
262 ks->bulk = algs->bulk->ops->genkeys(algs->bulk, &rk);
263 ks->bulk->ops = algs->bulk->ops;
264
265 T( ks->seq = seq++; )
266 ks->ref = 1;
267 ks->t_exp = now + T_EXP;
268 ks->sz_exp = algs->bulk->ops->expsz(algs->bulk);
269 ks->sz_regen = ks->sz_exp/2;
270 ks->oseq = 0;
271 seq_reset(&ks->iseq);
272 ks->next = 0;
273 ks->p = p;
274 ks->f = KSF_LISTEN;
275 return (ks);
276 }
277
278 /* --- @ks_activate@ --- *
279 *
280 * Arguments: @keyset *ks@ = pointer to a keyset
281 *
282 * Returns: ---
283 *
284 * Use: Activates a keyset, so that it can be used for encrypting
285 * outgoing messages.
286 */
287
288 void ks_activate(keyset *ks)
289 {
290 if (ks->f & KSF_LISTEN) {
291 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
292 ks->f &= ~KSF_LISTEN;
293 }
294 }
295
296 /* --- @ks_encrypt@ --- *
297 *
298 * Arguments: @keyset *ks@ = pointer to a keyset
299 * @unsigned ty@ = message type
300 * @buf *b@ = pointer to input buffer
301 * @buf *bb@ = pointer to output buffer
302 *
303 * Returns: Zero if successful; @KSERR_REGEN@ if we should negotiate a
304 * new key; @KSERR_NOKEYS@ if the key is not usable. Also
305 * returns zero if there was insufficient buffer (but the output
306 * buffer is broken in this case).
307 *
308 * Use: Encrypts a block of data using the key. Note that the `key
309 * ought to be replaced' notification is only ever given once
310 * for each key. Also note that this call forces a keyset to be
311 * used even if it's marked as not for data output.
312 *
313 * The encryption transform is permitted to corrupt @buf_u@ for
314 * its own purposes. Neither the source nor destination should
315 * be within @buf_u@; and callers mustn't expect anything stored
316 * in @buf_u@ to still
317 */
318
319 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
320 {
321 time_t now = time(0);
322
323 if (!KEYOK(ks, now)) {
324 buf_break(bb);
325 return (KSERR_NOKEYS);
326 }
327 return (doencrypt(ks, ty, b, bb));
328 }
329
330 /* --- @ks_decrypt@ --- *
331 *
332 * Arguments: @keyset *ks@ = pointer to a keyset
333 * @unsigned ty@ = expected type code
334 * @buf *b@ = pointer to an input buffer
335 * @buf *bb@ = pointer to an output buffer
336 *
337 * Returns: Zero on success; @KSERR_...@ on failure. Also returns
338 * zero if there was insufficient buffer (but the output buffer
339 * is broken in this case).
340 *
341 * Use: Attempts to decrypt a message using a given key. Note that
342 * requesting decryption with a key directly won't clear a
343 * marking that it's not for encryption.
344 *
345 * The decryption transform is permitted to corrupt @buf_u@ for
346 * its own purposes. Neither the source nor destination should
347 * be within @buf_u@; and callers mustn't expect anything stored
348 * in @buf_u@ to still
349 */
350
351 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
352 {
353 time_t now = time(0);
354 uint32 seq;
355 int err;
356
357 if (!KEYOK(ks, now)) return (KSERR_DECRYPT);
358 if (buf_ensure(bb, BLEN(b))) return (0);
359 if ((err = dodecrypt(ks, ty, b, bb, &seq)) != 0) return (err);
360 if (seq_check(&ks->iseq, seq, "SYMM")) return (KSERR_SEQ);
361 return (0);
362 }
363
364 /*----- Keyset list handling ----------------------------------------------*/
365
366 /* --- @ksl_free@ --- *
367 *
368 * Arguments: @keyset **ksroot@ = pointer to keyset list head
369 *
370 * Returns: ---
371 *
372 * Use: Frees (releases references to) all of the keys in a keyset.
373 */
374
375 void ksl_free(keyset **ksroot)
376 {
377 keyset *ks, *ksn;
378 for (ks = *ksroot; ks; ks = ksn) {
379 ksn = ks->next;
380 ks->f &= ~KSF_LINK;
381 ks_drop(ks);
382 }
383 }
384
385 /* --- @ksl_link@ --- *
386 *
387 * Arguments: @keyset **ksroot@ = pointer to keyset list head
388 * @keyset *ks@ = pointer to a keyset
389 *
390 * Returns: ---
391 *
392 * Use: Links a keyset into a list. A keyset can only be on one list
393 * at a time. Bad things happen otherwise.
394 */
395
396 void ksl_link(keyset **ksroot, keyset *ks)
397 {
398 assert(!(ks->f & KSF_LINK));
399 ks->next = *ksroot;
400 *ksroot = ks;
401 ks->f |= KSF_LINK;
402 ks->ref++;
403 }
404
405 /* --- @ksl_prune@ --- *
406 *
407 * Arguments: @keyset **ksroot@ = pointer to keyset list head
408 *
409 * Returns: ---
410 *
411 * Use: Prunes the keyset list by removing keys which mustn't be used
412 * any more.
413 */
414
415 void ksl_prune(keyset **ksroot)
416 {
417 time_t now = time(0);
418
419 while (*ksroot) {
420 keyset *ks = *ksroot;
421
422 if (ks->t_exp <= now) {
423 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
424 ks->seq); )
425 goto kill;
426 } else if (ks->sz_exp == 0) {
427 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
428 ks->seq); )
429 goto kill;
430 } else {
431 ksroot = &ks->next;
432 continue;
433 }
434
435 kill:
436 *ksroot = ks->next;
437 ks->f &= ~KSF_LINK;
438 ks_drop(ks);
439 }
440 }
441
442 /* --- @ksl_encrypt@ --- *
443 *
444 * Arguments: @keyset **ksroot@ = pointer to keyset list head
445 * @unsigned ty@ = message type
446 * @buf *b@ = pointer to input buffer
447 * @buf *bb@ = pointer to output buffer
448 *
449 * Returns: Zero if successful; @KSERR_REGEN@ if it's time to negotiate a
450 * new key; @KSERR_NOKEYS@ if there are no suitable keys
451 * available. Also returns zero if there was insufficient
452 * buffer space (but the output buffer is broken in this case).
453 *
454 * Use: Encrypts a packet.
455 */
456
457 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
458 {
459 time_t now = time(0);
460 keyset *ks = *ksroot;
461
462 for (;;) {
463 if (!ks) {
464 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
465 buf_break(bb);
466 return (KSERR_NOKEYS);
467 }
468 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
469 break;
470 ks = ks->next;
471 }
472
473 return (doencrypt(ks, ty, b, bb));
474 }
475
476 /* --- @ksl_decrypt@ --- *
477 *
478 * Arguments: @keyset **ksroot@ = pointer to keyset list head
479 * @unsigned ty@ = expected type code
480 * @buf *b@ = pointer to input buffer
481 * @buf *bb@ = pointer to output buffer
482 *
483 * Returns: Zero on success; @KSERR_DECRYPT@ on failure. Also returns
484 * zero if there was insufficient buffer (but the output buffer
485 * is broken in this case).
486 *
487 * Use: Decrypts a packet.
488 */
489
490 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
491 {
492 time_t now = time(0);
493 keyset *ks;
494 uint32 seq;
495 int err;
496
497 if (buf_ensure(bb, BLEN(b)))
498 return (0);
499
500 for (ks = *ksroot; ks; ks = ks->next) {
501 if (!KEYOK(ks, now))
502 continue;
503 if ((err = dodecrypt(ks, ty, b, bb, &seq)) == 0) {
504 if (ks->f & KSF_LISTEN) {
505 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
506 ks->seq); )
507 ks->f &= ~KSF_LISTEN;
508 }
509 if (seq_check(&ks->iseq, seq, "SYMM"))
510 return (KSERR_SEQ);
511 else
512 return (0);
513 }
514 if (err != KSERR_DECRYPT) return (err);
515 }
516 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
517 return (KSERR_DECRYPT);
518 }
519
520 /*----- That's all, folks -------------------------------------------------*/