3 * Handling of symmetric keysets
5 * (c) 2001 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Trivial IP Encryption (TrIPE).
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.
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.
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.
27 /*----- Header files ------------------------------------------------------*/
31 /*----- Handy macros ------------------------------------------------------*/
33 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
35 /*----- Low-level packet encryption and decryption ------------------------*/
37 /* --- Encrypted data format --- *
39 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
42 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
44 * as the CBC-ciphertext of %$p_i$%, and then
46 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
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].
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].
61 /* --- @doencrypt@ --- *
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
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.
72 * Use: Encrypts a message with the given key. We assume that the
73 * keyset is OK to use.
76 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
82 /* --- Initial tracing --- */
84 IF_TRACING(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);
91 /* --- Apply the bulk-crypto transformation --- */
93 rc = ks->bulk->encrypt(ks, ty, b, bb);
94 if (rc || !BOK(bb)) return (rc);
96 /* --- Do the necessary accounting for data volume --- */
99 nsz = osz > sz ? osz - sz : 0;
100 if (osz >= ks->sz_regen && ks->sz_regen > nsz) {
101 T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
102 "forcing exchange", ks->seq); )
107 /* --- We're done --- */
112 /* --- @dodecrypt@ --- *
114 * Arguments: @keyset *ks@ = pointer to keyset to use
115 * @unsigned ty@ = expected type code
116 * @buf *b@ = pointer to an input buffer
117 * @buf *bb@ = pointer to an output buffer
118 * @uint32 *seq@ = where to store the sequence number
120 * Returns: Zero on success; @KSERR_DECRYPT@ on failure.
122 * Use: Attempts to decrypt a message with the given key. No other
123 * checking (e.g., sequence number checks) is performed. We
124 * assume that the keyset is OK to use, and that there is
125 * sufficient output buffer space reserved. If the decryption
126 * is successful, the buffer pointer is moved past the decrypted
127 * packet, and the packet's sequence number is stored in @*seq@.
130 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
132 const octet *q = BCUR(bb);
135 IF_TRACING(T_KEYSET, {
137 "keyset: try decrypting packet (type %u) using keyset %u",
139 trace_block(T_CRYPTO, "crypto: ciphertext packet", BCUR(b), BLEFT(b));
142 rc = ks->bulk->decrypt(ks, ty, b, bb, seq);
145 IF_TRACING(T_KEYSET, {
146 trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
147 (unsigned long)*seq);
148 trace_block(T_CRYPTO, "crypto: decrypted packet", q, BCUR(bb) - q);
153 /*----- Operations on a single keyset -------------------------------------*/
155 /* --- @ks_drop@ --- *
157 * Arguments: @keyset *ks@ = pointer to a keyset
161 * Use: Decrements a keyset's reference counter. If the counter hits
162 * zero, the keyset is freed.
165 void ks_drop(keyset *ks)
170 #define DROP(dir, a, drop) do { if (ks->dir.a) drop(ks->dir.a); } while (0)
171 #define DROP_DIR(dir) do { \
172 DROP(dir, c, GC_DESTROY); \
173 DROP(dir, m, GM_DESTROY); \
185 /* --- @ks_gen@ --- *
187 * Arguments: @const void *k@ = pointer to key material
188 * @size_t x, y, z@ = offsets into key material (see below)
189 * @peer *p@ = pointer to peer information
191 * Returns: A pointer to the new keyset.
193 * Use: Derives a new keyset from the given key material. The
194 * offsets @x@, @y@ and @z@ separate the key material into three
195 * parts. Between the @k@ and @k + x@ is `my' contribution to
196 * the key material; between @k + x@ and @k + y@ is `your'
197 * contribution; and between @k + y@ and @k + z@ is a shared
198 * value we made together. These are used to construct two
199 * pairs of symmetric keys. Each pair consists of an encryption
200 * key and a message authentication key. One pair is used for
201 * outgoing messages, the other for incoming messages.
203 * The new key is marked so that it won't be selected for output
204 * by @ksl_encrypt@. You can still encrypt data with it by
205 * calling @ks_encrypt@ directly.
208 static void gen_dir(const algswitch *algs, struct ksdir *ksd,
209 const char *whichdir,
210 const octet *from, size_t fromsz,
211 const octet *to, size_t tosz,
212 const octet *both, size_t bothsz)
214 #define SETKEY(what, a, init) do { \
221 _h = GH_INIT(algs->h); \
222 HASH_STRING(_h, "tripe-" what); \
223 GH_HASH(_h, from, fromsz); \
224 GH_HASH(_h, to, tosz); \
225 GH_HASH(_h, both, bothsz); \
226 _hh = GH_DONE(_h, 0); \
227 IF_TRACING(T_KEYSET, { IF_TRACING(T_CRYPTO, { \
229 sprintf(_buf, "crypto: %s key " what, whichdir); \
230 trace_block(T_CRYPTO, _buf, _hh, algs->a##ksz); \
232 ksd->a = init(algs->a, _hh, algs->a##ksz); \
237 SETKEY("encryption", c, GC_INIT);
238 SETKEY("integrity", m, GM_KEY);
243 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
245 keyset *ks = CREATE(keyset);
246 time_t now = time(0);
248 const algswitch *algs = &p->kx.kpriv->algs;
249 T( static unsigned seq = 0; )
251 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
253 gen_dir(algs, &ks->in, "incoming", pp, x, pp + x, y - x, pp + y, z - y);
254 gen_dir(algs, &ks->out, "outgoing", pp + x, y - x, pp, x, pp + y, z - y);
256 T( ks->seq = seq++; )
257 ks->bulk = algs->bulk;
259 ks->t_exp = now + T_EXP;
260 ks->sz_exp = algs->expsz;
261 ks->sz_regen = algs->expsz/2;
263 seq_reset(&ks->iseq);
267 ks->tagsz = algs->tagsz;
271 /* --- @ks_activate@ --- *
273 * Arguments: @keyset *ks@ = pointer to a keyset
277 * Use: Activates a keyset, so that it can be used for encrypting
281 void ks_activate(keyset *ks)
283 if (ks->f & KSF_LISTEN) {
284 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
285 ks->f &= ~KSF_LISTEN;
289 /* --- @ks_encrypt@ --- *
291 * Arguments: @keyset *ks@ = pointer to a keyset
292 * @unsigned ty@ = message type
293 * @buf *b@ = pointer to input buffer
294 * @buf *bb@ = pointer to output buffer
296 * Returns: Zero if successful; @KSERR_REGEN@ if we should negotiate a
297 * new key; @KSERR_NOKEYS@ if the key is not usable. Also
298 * returns zero if there was insufficient buffer (but the output
299 * buffer is broken in this case).
301 * Use: Encrypts a block of data using the key. Note that the `key
302 * ought to be replaced' notification is only ever given once
303 * for each key. Also note that this call forces a keyset to be
304 * used even if it's marked as not for data output.
306 * The encryption transform is permitted to corrupt @buf_u@ for
307 * its own purposes. Neither the source nor destination should
308 * be within @buf_u@; and callers mustn't expect anything stored
309 * in @buf_u@ to still
312 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
314 time_t now = time(0);
316 if (!KEYOK(ks, now)) {
318 return (KSERR_NOKEYS);
320 return (doencrypt(ks, ty, b, bb));
323 /* --- @ks_decrypt@ --- *
325 * Arguments: @keyset *ks@ = pointer to a keyset
326 * @unsigned ty@ = expected type code
327 * @buf *b@ = pointer to an input buffer
328 * @buf *bb@ = pointer to an output buffer
330 * Returns: Zero on success; @KSERR_...@ on failure. Also returns
331 * zero if there was insufficient buffer (but the output buffer
332 * is broken in this case).
334 * Use: Attempts to decrypt a message using a given key. Note that
335 * requesting decryption with a key directly won't clear a
336 * marking that it's not for encryption.
338 * The decryption transform is permitted to corrupt @buf_u@ for
339 * its own purposes. Neither the source nor destination should
340 * be within @buf_u@; and callers mustn't expect anything stored
341 * in @buf_u@ to still
344 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
346 time_t now = time(0);
350 if (!KEYOK(ks, now)) return (KSERR_DECRYPT);
351 if (buf_ensure(bb, BLEN(b))) return (0);
352 if ((err = dodecrypt(ks, ty, b, bb, &seq)) != 0) return (err);
353 if (seq_check(&ks->iseq, seq, "SYMM")) return (KSERR_SEQ);
357 /*----- Keyset list handling ----------------------------------------------*/
359 /* --- @ksl_free@ --- *
361 * Arguments: @keyset **ksroot@ = pointer to keyset list head
365 * Use: Frees (releases references to) all of the keys in a keyset.
368 void ksl_free(keyset **ksroot)
371 for (ks = *ksroot; ks; ks = ksn) {
378 /* --- @ksl_link@ --- *
380 * Arguments: @keyset **ksroot@ = pointer to keyset list head
381 * @keyset *ks@ = pointer to a keyset
385 * Use: Links a keyset into a list. A keyset can only be on one list
386 * at a time. Bad things happen otherwise.
389 void ksl_link(keyset **ksroot, keyset *ks)
391 assert(!(ks->f & KSF_LINK));
398 /* --- @ksl_prune@ --- *
400 * Arguments: @keyset **ksroot@ = pointer to keyset list head
404 * Use: Prunes the keyset list by removing keys which mustn't be used
408 void ksl_prune(keyset **ksroot)
410 time_t now = time(0);
413 keyset *ks = *ksroot;
415 if (ks->t_exp <= now) {
416 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
419 } else if (ks->sz_exp == 0) {
420 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
435 /* --- @ksl_encrypt@ --- *
437 * Arguments: @keyset **ksroot@ = pointer to keyset list head
438 * @unsigned ty@ = message type
439 * @buf *b@ = pointer to input buffer
440 * @buf *bb@ = pointer to output buffer
442 * Returns: Zero if successful; @KSERR_REGEN@ if it's time to negotiate a
443 * new key; @KSERR_NOKEYS@ if there are no suitable keys
444 * available. Also returns zero if there was insufficient
445 * buffer space (but the output buffer is broken in this case).
447 * Use: Encrypts a packet.
450 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
452 time_t now = time(0);
453 keyset *ks = *ksroot;
457 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
459 return (KSERR_NOKEYS);
461 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
466 return (doencrypt(ks, ty, b, bb));
469 /* --- @ksl_decrypt@ --- *
471 * Arguments: @keyset **ksroot@ = pointer to keyset list head
472 * @unsigned ty@ = expected type code
473 * @buf *b@ = pointer to input buffer
474 * @buf *bb@ = pointer to output buffer
476 * Returns: Zero on success; @KSERR_DECRYPT@ on failure. Also returns
477 * zero if there was insufficient buffer (but the output buffer
478 * is broken in this case).
480 * Use: Decrypts a packet.
483 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
485 time_t now = time(0);
490 if (buf_ensure(bb, BLEN(b)))
493 for (ks = *ksroot; ks; ks = ks->next) {
496 if ((err = dodecrypt(ks, ty, b, bb, &seq)) == 0) {
497 if (ks->f & KSF_LISTEN) {
498 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
500 ks->f &= ~KSF_LISTEN;
502 if (seq_check(&ks->iseq, seq, "SYMM"))
507 if (err != KSERR_DECRYPT) return (err);
509 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
510 return (KSERR_DECRYPT);
513 /*----- That's all, folks -------------------------------------------------*/