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->ops->encrypt(ks->bulk, ty, b, bb, ks->oseq);
94 if (rc || !BOK(bb)) return (rc);
97 /* --- Do the necessary accounting for data volume --- */
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); )
108 /* --- We're done --- */
113 /* --- @dodecrypt@ --- *
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
121 * Returns: Zero on success; @KSERR_DECRYPT@ on failure.
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@.
131 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
133 const octet *q = BCUR(bb);
136 IF_TRACING(T_KEYSET, {
138 "keyset: try decrypting packet (type %u) using keyset %u",
140 trace_block(T_CRYPTO, "crypto: ciphertext packet", BCUR(b), BLEFT(b));
143 rc = ks->bulk->ops->decrypt(ks->bulk, ty, b, bb, seq);
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);
154 /*----- Operations on a single keyset -------------------------------------*/
156 /* --- @ks_drop@ --- *
158 * Arguments: @keyset *ks@ = pointer to a keyset
162 * Use: Decrements a keyset's reference counter. If the counter hits
163 * zero, the keyset is freed.
166 void ks_drop(keyset *ks)
168 if (--ks->ref) return;
169 ks->bulk->ops->freectx(ks->bulk);
173 /* --- @ks_derivekey@ --- *
175 * Arguments: @octet *k@ = pointer to an output buffer of at least
177 * @size_t ksz@ = actual size wanted (for tracing)
178 * @const struct rawkey *rk@ = a raw key, as passed into
180 * @int dir@ = direction for the key (@DIR_IN@ or @DIR_OUT@)
181 * @const char *what@ = label for the key (input to derivation)
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.
196 void ks_derivekey(octet *k, size_t ksz, const struct rawkey *rk,
197 int dir, const char *what)
199 const gchash *hc = rk->hc;
202 assert(ksz <= hc->hashsz);
203 assert(hc->hashsz <= MAXHASHSZ);
205 GH_HASH(h, "tripe-", 6); GH_HASH(h, what, strlen(what) + 1);
208 GH_HASH(h, rk->k, rk->x);
209 GH_HASH(h, rk->k + rk->x, rk->y - rk->x);
212 GH_HASH(h, rk->k + rk->x, rk->y - rk->x);
213 GH_HASH(h, rk->k, rk->x);
218 GH_HASH(h, rk->k + rk->y, rk->z - rk->y);
221 IF_TRACING(T_KEYSET, { IF_TRACING(T_CRYPTO, {
223 sprintf(_buf, "crypto: %s key %s", dir ? "incoming" : "outgoing", what);
224 trace_block(T_CRYPTO, _buf, k, ksz);
228 /* --- @ks_gen@ --- *
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
234 * Returns: A pointer to the new keyset.
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.
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.
251 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
253 keyset *ks = CREATE(keyset);
254 time_t now = time(0);
255 const algswitch *algs = &p->kx.kpriv->algs;
257 T( static unsigned seq = 0; )
259 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
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;
265 T( ks->seq = seq++; )
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;
271 seq_reset(&ks->iseq);
278 /* --- @ks_activate@ --- *
280 * Arguments: @keyset *ks@ = pointer to a keyset
284 * Use: Activates a keyset, so that it can be used for encrypting
288 void ks_activate(keyset *ks)
290 if (ks->f & KSF_LISTEN) {
291 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
292 ks->f &= ~KSF_LISTEN;
296 /* --- @ks_encrypt@ --- *
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
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).
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.
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
319 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
321 time_t now = time(0);
323 if (!KEYOK(ks, now)) {
325 return (KSERR_NOKEYS);
327 return (doencrypt(ks, ty, b, bb));
330 /* --- @ks_decrypt@ --- *
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
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).
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.
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
351 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
353 time_t now = time(0);
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);
364 /*----- Keyset list handling ----------------------------------------------*/
366 /* --- @ksl_free@ --- *
368 * Arguments: @keyset **ksroot@ = pointer to keyset list head
372 * Use: Frees (releases references to) all of the keys in a keyset.
375 void ksl_free(keyset **ksroot)
378 for (ks = *ksroot; ks; ks = ksn) {
385 /* --- @ksl_link@ --- *
387 * Arguments: @keyset **ksroot@ = pointer to keyset list head
388 * @keyset *ks@ = pointer to a keyset
392 * Use: Links a keyset into a list. A keyset can only be on one list
393 * at a time. Bad things happen otherwise.
396 void ksl_link(keyset **ksroot, keyset *ks)
398 assert(!(ks->f & KSF_LINK));
405 /* --- @ksl_prune@ --- *
407 * Arguments: @keyset **ksroot@ = pointer to keyset list head
411 * Use: Prunes the keyset list by removing keys which mustn't be used
415 void ksl_prune(keyset **ksroot)
417 time_t now = time(0);
420 keyset *ks = *ksroot;
422 if (ks->t_exp <= now) {
423 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
426 } else if (ks->sz_exp == 0) {
427 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
442 /* --- @ksl_encrypt@ --- *
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
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).
454 * Use: Encrypts a packet.
457 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
459 time_t now = time(0);
460 keyset *ks = *ksroot;
464 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
466 return (KSERR_NOKEYS);
468 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
473 return (doencrypt(ks, ty, b, bb));
476 /* --- @ksl_decrypt@ --- *
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
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).
487 * Use: Decrypts a packet.
490 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
492 time_t now = time(0);
497 if (buf_ensure(bb, BLEN(b)))
500 for (ks = *ksroot; ks; ks = ks->next) {
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",
507 ks->f &= ~KSF_LISTEN;
509 if (seq_check(&ks->iseq, seq, "SYMM"))
514 if (err != KSERR_DECRYPT) return (err);
516 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
517 return (KSERR_DECRYPT);
520 /*----- That's all, folks -------------------------------------------------*/