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 it under
13 * the terms of the GNU General Public License as published by the Free
14 * Software Foundation; either version 3 of the License, or (at your
15 * option) any later version.
17 * TrIPE is distributed in the hope that it will be useful, but WITHOUT
18 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
19 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
22 * You should have received a copy of the GNU General Public License
23 * along with TrIPE. If not, see <https://www.gnu.org/licenses/>.
26 /*----- Header files ------------------------------------------------------*/
30 /*----- Handy macros ------------------------------------------------------*/
32 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
34 /*----- Low-level packet encryption and decryption ------------------------*/
36 /* --- Encrypted data format --- *
38 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
41 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
43 * as the CBC-ciphertext of %$p_i$%, and then
45 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
47 * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
48 * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
49 * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
50 * [Bellare and Namprempre].
52 * This also ensures that, assuming the key is good, we have a secure channel
53 * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
54 * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
55 * then-encrypt scheme and still have a secure channel. However, I like the
56 * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
57 * the Horton Principle [Wagner and Schneier].
60 /* --- @doencrypt@ --- *
62 * Arguments: @keyset *ks@ = pointer to keyset to use
63 * @unsigned ty@ = type of message this is
64 * @buf *b@ = pointer to an input buffer
65 * @buf *bb@ = pointer to an output buffer
67 * Returns: Zero if OK; @KSERR_REGEN@ if it's time to generate new keys.
68 * Also returns zero if there was insufficient buffer space, but
69 * the buffer is broken in this case.
71 * Use: Encrypts a message with the given key. We assume that the
72 * keyset is OK to use.
75 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
81 /* --- Initial tracing --- */
83 IF_TRACING(T_KEYSET, {
85 "keyset: encrypting packet %lu (type 0x%02x) using keyset %u",
86 (unsigned long)ks->oseq, ty, ks->seq);
87 trace_block(T_CRYPTO, "crypto: plaintext packet", BCUR(b), sz);
90 /* --- Apply the bulk-crypto transformation --- */
92 rc = ks->bulk->ops->encrypt(ks->bulk, ty, b, bb, ks->oseq);
93 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 0x%02x) using keyset %u",
139 trace_block(T_CRYPTO, "crypto: ciphertext packet", BCUR(b), BLEFT(b));
142 rc = ks->bulk->ops->decrypt(ks->bulk, 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)
167 if (--ks->ref) return;
168 ks->bulk->ops->freectx(ks->bulk);
172 /* --- @ks_gen@ --- *
174 * Arguments: @deriveargs *a@ = key derivation parameters (modified)
175 * @peer *p@ = pointer to peer information
177 * Returns: A pointer to the new keyset.
179 * Use: Derives a new keyset from the given key material. This will
180 * set the @what@, @f@, and @hc@ members in @*a@; other members
181 * must be filled in by the caller.
183 * The new key is marked so that it won't be selected for output
184 * by @ksl_encrypt@. You can still encrypt data with it by
185 * calling @ks_encrypt@ directly.
188 keyset *ks_gen(deriveargs *a, peer *p)
190 keyset *ks = CREATE(keyset);
191 time_t now = time(0);
192 const algswitch *algs = &p->kx.kpriv->algs;
193 T( static unsigned seq = 0; )
195 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
197 a->what = "tripe-"; a->f = DF_IN | DF_OUT; a->hc = algs->h;
198 ks->bulk = algs->bulk->ops->genkeys(algs->bulk, a);
199 ks->bulk->ops = algs->bulk->ops;
201 T( ks->seq = seq++; )
203 ks->t_exp = now + T_EXP;
204 ks->sz_exp = algs->bulk->ops->expsz(algs->bulk);
205 ks->sz_regen = ks->sz_exp/2;
207 seq_reset(&ks->iseq);
214 /* --- @ks_activate@ --- *
216 * Arguments: @keyset *ks@ = pointer to a keyset
220 * Use: Activates a keyset, so that it can be used for encrypting
224 void ks_activate(keyset *ks)
226 if (ks->f & KSF_LISTEN) {
227 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
228 ks->f &= ~KSF_LISTEN;
232 /* --- @ks_encrypt@ --- *
234 * Arguments: @keyset *ks@ = pointer to a keyset
235 * @unsigned ty@ = message type
236 * @buf *b@ = pointer to input buffer
237 * @buf *bb@ = pointer to output buffer
239 * Returns: Zero if successful; @KSERR_REGEN@ if we should negotiate a
240 * new key; @KSERR_NOKEYS@ if the key is not usable. Also
241 * returns zero if there was insufficient buffer (but the output
242 * buffer is broken in this case).
244 * Use: Encrypts a block of data using the key. Note that the `key
245 * ought to be replaced' notification is only ever given once
246 * for each key. Also note that this call forces a keyset to be
247 * used even if it's marked as not for data output.
249 * The encryption transform is permitted to corrupt @buf_u@ for
250 * its own purposes. Neither the source nor destination should
251 * be within @buf_u@; and callers mustn't expect anything stored
252 * in @buf_u@ to still
255 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
257 time_t now = time(0);
259 if (!KEYOK(ks, now)) {
261 return (KSERR_NOKEYS);
263 return (doencrypt(ks, ty, b, bb));
266 /* --- @ks_decrypt@ --- *
268 * Arguments: @keyset *ks@ = pointer to a keyset
269 * @unsigned ty@ = expected type code
270 * @buf *b@ = pointer to an input buffer
271 * @buf *bb@ = pointer to an output buffer
273 * Returns: Zero on success; @KSERR_...@ on failure. Also returns
274 * zero if there was insufficient buffer (but the output buffer
275 * is broken in this case).
277 * Use: Attempts to decrypt a message using a given key. Note that
278 * requesting decryption with a key directly won't clear a
279 * marking that it's not for encryption.
281 * The decryption transform is permitted to corrupt @buf_u@ for
282 * its own purposes. Neither the source nor destination should
283 * be within @buf_u@; and callers mustn't expect anything stored
284 * in @buf_u@ to still
287 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
289 time_t now = time(0);
293 if (!KEYOK(ks, now)) return (KSERR_DECRYPT);
294 if (buf_ensure(bb, BLEN(b))) return (0);
295 if ((err = dodecrypt(ks, ty, b, bb, &seq)) != 0) return (err);
296 if (seq_check(&ks->iseq, seq, "SYMM")) return (KSERR_SEQ);
300 /*----- Keyset list handling ----------------------------------------------*/
302 /* --- @ksl_free@ --- *
304 * Arguments: @keyset **ksroot@ = pointer to keyset list head
308 * Use: Frees (releases references to) all of the keys in a keyset.
311 void ksl_free(keyset **ksroot)
314 for (ks = *ksroot; ks; ks = ksn) {
321 /* --- @ksl_link@ --- *
323 * Arguments: @keyset **ksroot@ = pointer to keyset list head
324 * @keyset *ks@ = pointer to a keyset
328 * Use: Links a keyset into a list. A keyset can only be on one list
329 * at a time. Bad things happen otherwise.
332 void ksl_link(keyset **ksroot, keyset *ks)
334 assert(!(ks->f & KSF_LINK));
341 /* --- @ksl_prune@ --- *
343 * Arguments: @keyset **ksroot@ = pointer to keyset list head
347 * Use: Prunes the keyset list by removing keys which mustn't be used
351 void ksl_prune(keyset **ksroot)
353 time_t now = time(0);
356 keyset *ks = *ksroot;
358 if (ks->t_exp <= now) {
359 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
362 } else if (ks->sz_exp == 0) {
363 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
378 /* --- @ksl_encrypt@ --- *
380 * Arguments: @keyset **ksroot@ = pointer to keyset list head
381 * @unsigned ty@ = message type
382 * @buf *b@ = pointer to input buffer
383 * @buf *bb@ = pointer to output buffer
385 * Returns: Zero if successful; @KSERR_REGEN@ if it's time to negotiate a
386 * new key; @KSERR_NOKEYS@ if there are no suitable keys
387 * available. Also returns zero if there was insufficient
388 * buffer space (but the output buffer is broken in this case).
390 * Use: Encrypts a packet.
393 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
395 time_t now = time(0);
396 keyset *ks = *ksroot;
400 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
402 return (KSERR_NOKEYS);
404 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
409 return (doencrypt(ks, ty, b, bb));
412 /* --- @ksl_decrypt@ --- *
414 * Arguments: @keyset **ksroot@ = pointer to keyset list head
415 * @unsigned ty@ = expected type code
416 * @buf *b@ = pointer to input buffer
417 * @buf *bb@ = pointer to output buffer
419 * Returns: Zero on success; @KSERR_DECRYPT@ on failure. Also returns
420 * zero if there was insufficient buffer (but the output buffer
421 * is broken in this case).
423 * Use: Decrypts a packet.
426 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
428 time_t now = time(0);
433 if (buf_ensure(bb, BLEN(b)))
436 for (ks = *ksroot; ks; ks = ks->next) {
439 if ((err = dodecrypt(ks, ty, b, bb, &seq)) == 0) {
440 if (ks->f & KSF_LISTEN) {
441 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
443 ks->f &= ~KSF_LISTEN;
445 if (seq_check(&ks->iseq, seq, "SYMM"))
450 if (err != KSERR_DECRYPT) return (err);
452 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
453 return (KSERR_DECRYPT);
456 /*----- That's all, folks -------------------------------------------------*/