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 #define SEQSZ 4 /* Size of sequence number packet */
37 /*----- Low-level packet encryption and decryption ------------------------*/
39 /* --- Encrypted data format --- *
41 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
44 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
46 * as the CBC-ciphertext of %$p_i$%, and then
48 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
50 * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
51 * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
52 * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
53 * [Bellare and Namprempre].
55 * This also ensures that, assuming the key is good, we have a secure channel
56 * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
57 * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
58 * then-encrypt scheme and still have a secure channel. However, I like the
59 * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
60 * the Horton Principle [Wagner and Schneier].
63 /* --- @doencrypt@ --- *
65 * Arguments: @keyset *ks@ = pointer to keyset to use
66 * @unsigned ty@ = type of message this is
67 * @buf *b@ = pointer to an input buffer
68 * @buf *bb@ = pointer to an output buffer
70 * Returns: Zero if OK; @KSERR_REGEN@ if it's time to generate new keys.
71 * Also returns zero if there was insufficient buffer space, but
72 * the buffer is broken in this case.
74 * Use: Encrypts a message with the given key. We assume that the
75 * keyset is OK to use.
78 static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
81 gcipher *c = ks->cout;
82 const octet *p = BCUR(b);
84 octet *qmac, *qseq, *qiv, *qpk;
86 size_t ivsz = GC_CLASS(c)->blksz;
87 size_t tagsz = ks->tagsz;
92 /* --- Allocate the required buffer space --- */
94 if (buf_ensure(bb, tagsz + SEQSZ + ivsz + sz))
95 return (0); /* Caution! */
96 qmac = BCUR(bb); qseq = qmac + tagsz; qiv = qseq + SEQSZ; qpk = qiv + ivsz;
97 BSTEP(bb, tagsz + SEQSZ + ivsz + sz);
100 oseq = ks->oseq++; STORE32(qseq, oseq);
101 IF_TRACING(T_KEYSET, {
102 trace(T_KEYSET, "keyset: encrypting packet %lu using keyset %u",
103 (unsigned long)oseq, ks->seq);
104 trace_block(T_CRYPTO, "crypto: plaintext packet", p, sz);
107 /* --- Encrypt the packet --- */
110 rand_get(RAND_GLOBAL, qiv, ivsz);
112 IF_TRACING(T_KEYSET, {
113 trace_block(T_CRYPTO, "crypto: initialization vector", qiv, ivsz);
116 GC_ENCRYPT(c, p, qpk, sz);
117 IF_TRACING(T_KEYSET, {
118 trace_block(T_CRYPTO, "crypto: encrypted packet", qpk, sz);
121 /* --- Now compute the MAC --- */
124 h = GM_INIT(ks->mout);
125 GH_HASH(h, t, sizeof(t));
126 GH_HASH(h, qseq, SEQSZ + ivsz + sz);
127 memcpy(qmac, GH_DONE(h, 0), tagsz);
129 IF_TRACING(T_KEYSET, {
130 trace_block(T_CRYPTO, "crypto: computed MAC", qmac, tagsz);
134 /* --- Deduct the packet size from the key's data life --- */
141 if (osz >= ks->sz_regen && ks->sz_regen > nsz) {
142 T( trace(T_KEYSET, "keyset: keyset %u data regen limit exceeded -- "
143 "forcing exchange", ks->seq); )
150 /* --- @dodecrypt@ --- *
152 * Arguments: @keyset *ks@ = pointer to keyset to use
153 * @unsigned ty@ = expected type code
154 * @buf *b@ = pointer to an input buffer
155 * @buf *bb@ = pointer to an output buffer
156 * @uint32 *seq@ = where to store the sequence number
158 * Returns: Zero on success; @KSERR_DECRYPT@ on failure.
160 * Use: Attempts to decrypt a message with the given key. No other
161 * checking (e.g., sequence number checks) is performed. We
162 * assume that the keyset is OK to use, and that there is
163 * sufficient output buffer space reserved. If the decryption
164 * is successful, the buffer pointer is moved past the decrypted
165 * packet, and the packet's sequence number is stored in @*seq@.
168 static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq)
170 const octet *pmac, *piv, *pseq, *ppk;
171 size_t psz = BLEFT(b);
175 gcipher *c = ks->cin;
176 size_t ivsz = GC_CLASS(c)->blksz;
177 size_t tagsz = ks->tagsz;
182 /* --- Break up the packet into its components --- */
184 if (psz < ivsz + SEQSZ + tagsz) {
185 T( trace(T_KEYSET, "keyset: block too small for keyset %u", ks->seq); )
186 return (KSERR_MALFORMED);
188 sz = psz - ivsz - SEQSZ - tagsz;
189 pmac = BCUR(b); pseq = pmac + tagsz; piv = pseq + SEQSZ; ppk = piv + ivsz;
192 IF_TRACING(T_KEYSET, {
193 trace(T_KEYSET, "keyset: decrypting using keyset %u", ks->seq);
194 trace_block(T_CRYPTO, "crypto: ciphertext packet", ppk, sz);
197 /* --- Verify the MAC on the packet --- */
200 h = GM_INIT(ks->min);
201 GH_HASH(h, t, sizeof(t));
202 GH_HASH(h, pseq, SEQSZ + ivsz + sz);
204 eq = ct_memeq(mac, pmac, tagsz);
205 IF_TRACING(T_KEYSET, {
206 trace_block(T_CRYPTO, "crypto: computed MAC", mac, tagsz);
210 IF_TRACING(T_KEYSET, {
211 trace(T_KEYSET, "keyset: incorrect MAC: decryption failed");
212 trace_block(T_CRYPTO, "crypto: expected MAC", pmac, tagsz);
214 return (KSERR_DECRYPT);
218 /* --- Decrypt the packet --- */
222 IF_TRACING(T_KEYSET, {
223 trace_block(T_CRYPTO, "crypto: initialization vector", piv, ivsz);
226 GC_DECRYPT(c, ppk, q, sz);
229 IF_TRACING(T_KEYSET, {
230 trace(T_KEYSET, "keyset: decrypted OK (sequence = %lu)",
231 (unsigned long)LOAD32(pseq));
232 trace_block(T_CRYPTO, "crypto: decrypted packet", q, sz);
238 /*----- Operations on a single keyset -------------------------------------*/
240 /* --- @ks_drop@ --- *
242 * Arguments: @keyset *ks@ = pointer to a keyset
246 * Use: Decrements a keyset's reference counter. If the counter hits
247 * zero, the keyset is freed.
250 void ks_drop(keyset *ks)
255 GC_DESTROY(ks->cout);
257 GM_DESTROY(ks->mout);
261 /* --- @ks_gen@ --- *
263 * Arguments: @const void *k@ = pointer to key material
264 * @size_t x, y, z@ = offsets into key material (see below)
265 * @peer *p@ = pointer to peer information
267 * Returns: A pointer to the new keyset.
269 * Use: Derives a new keyset from the given key material. The
270 * offsets @x@, @y@ and @z@ separate the key material into three
271 * parts. Between the @k@ and @k + x@ is `my' contribution to
272 * the key material; between @k + x@ and @k + y@ is `your'
273 * contribution; and between @k + y@ and @k + z@ is a shared
274 * value we made together. These are used to construct two
275 * pairs of symmetric keys. Each pair consists of an encryption
276 * key and a message authentication key. One pair is used for
277 * outgoing messages, the other for incoming messages.
279 * The new key is marked so that it won't be selected for output
280 * by @ksl_encrypt@. You can still encrypt data with it by
281 * calling @ks_encrypt@ directly.
284 keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p)
288 keyset *ks = CREATE(keyset);
289 time_t now = time(0);
291 const algswitch *algs = &p->kx.kpriv->algs;
292 T( static unsigned seq = 0; )
294 T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); )
296 /* --- Construct the various keys --- *
298 * This is done with macros, because it's quite tedious.
301 #define MINE GH_HASH(h, pp, x)
302 #define YOURS GH_HASH(h, pp + x, y - x)
303 #define OURS GH_HASH(h, pp + y, z - y)
305 #define HASH_in MINE; YOURS; OURS
306 #define HASH_out YOURS; MINE; OURS
307 #define INIT_c(k) GC_INIT(algs->c, (k), algs->cksz)
308 #define INIT_m(k) GM_KEY(algs->m, (k), algs->mksz)
309 #define STR_c "encryption"
310 #define STR_m "integrity"
311 #define STR_in "incoming"
312 #define STR_out "outgoing"
314 #define SETKEY(a, dir) do { \
315 h = GH_INIT(algs->h); \
316 HASH_STRING(h, "tripe-" STR_##a); \
318 hh = GH_DONE(h, 0); \
319 IF_TRACING(T_KEYSET, { \
320 trace_block(T_CRYPTO, "crypto: " STR_##dir " key " STR_##a, \
323 ks->a##dir = INIT_##a(hh); \
327 SETKEY(c, in); SETKEY(c, out);
328 SETKEY(m, in); SETKEY(m, out);
343 T( ks->seq = seq++; )
345 ks->t_exp = now + T_EXP;
346 ks->sz_exp = algs->expsz;
347 ks->sz_regen = algs->expsz/2;
349 seq_reset(&ks->iseq);
353 ks->tagsz = algs->tagsz;
357 /* --- @ks_activate@ --- *
359 * Arguments: @keyset *ks@ = pointer to a keyset
363 * Use: Activates a keyset, so that it can be used for encrypting
367 void ks_activate(keyset *ks)
369 if (ks->f & KSF_LISTEN) {
370 T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); )
371 ks->f &= ~KSF_LISTEN;
375 /* --- @ks_encrypt@ --- *
377 * Arguments: @keyset *ks@ = pointer to a keyset
378 * @unsigned ty@ = message type
379 * @buf *b@ = pointer to input buffer
380 * @buf *bb@ = pointer to output buffer
382 * Returns: Zero if successful; @KSERR_REGEN@ if we should negotiate a
383 * new key; @KSERR_NOKEYS@ if the key is not usable. Also
384 * returns zero if there was insufficient buffer (but the output
385 * buffer is broken in this case).
387 * Use: Encrypts a block of data using the key. Note that the `key
388 * ought to be replaced' notification is only ever given once
389 * for each key. Also note that this call forces a keyset to be
390 * used even if it's marked as not for data output.
393 int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
395 time_t now = time(0);
397 if (!KEYOK(ks, now)) {
399 return (KSERR_NOKEYS);
401 return (doencrypt(ks, ty, b, bb));
404 /* --- @ks_decrypt@ --- *
406 * Arguments: @keyset *ks@ = pointer to a keyset
407 * @unsigned ty@ = expected type code
408 * @buf *b@ = pointer to an input buffer
409 * @buf *bb@ = pointer to an output buffer
411 * Returns: Zero on success; @KSERR_...@ on failure. Also returns
412 * zero if there was insufficient buffer (but the output buffer
413 * is broken in this case).
415 * Use: Attempts to decrypt a message using a given key. Note that
416 * requesting decryption with a key directly won't clear a
417 * marking that it's not for encryption.
420 int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb)
422 time_t now = time(0);
426 if (!KEYOK(ks, now)) return (KSERR_DECRYPT);
427 if (buf_ensure(bb, BLEN(b))) return (0);
428 if ((err = dodecrypt(ks, ty, b, bb, &seq)) != 0) return (err);
429 if (seq_check(&ks->iseq, seq, "SYMM")) return (KSERR_SEQ);
433 /*----- Keyset list handling ----------------------------------------------*/
435 /* --- @ksl_free@ --- *
437 * Arguments: @keyset **ksroot@ = pointer to keyset list head
441 * Use: Frees (releases references to) all of the keys in a keyset.
444 void ksl_free(keyset **ksroot)
447 for (ks = *ksroot; ks; ks = ksn) {
454 /* --- @ksl_link@ --- *
456 * Arguments: @keyset **ksroot@ = pointer to keyset list head
457 * @keyset *ks@ = pointer to a keyset
461 * Use: Links a keyset into a list. A keyset can only be on one list
462 * at a time. Bad things happen otherwise.
465 void ksl_link(keyset **ksroot, keyset *ks)
467 assert(!(ks->f & KSF_LINK));
474 /* --- @ksl_prune@ --- *
476 * Arguments: @keyset **ksroot@ = pointer to keyset list head
480 * Use: Prunes the keyset list by removing keys which mustn't be used
484 void ksl_prune(keyset **ksroot)
486 time_t now = time(0);
489 keyset *ks = *ksroot;
491 if (ks->t_exp <= now) {
492 T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)",
495 } else if (ks->sz_exp == 0) {
496 T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)",
511 /* --- @ksl_encrypt@ --- *
513 * Arguments: @keyset **ksroot@ = pointer to keyset list head
514 * @unsigned ty@ = message type
515 * @buf *b@ = pointer to input buffer
516 * @buf *bb@ = pointer to output buffer
518 * Returns: Zero if successful; @KSERR_REGEN@ if it's time to negotiate a
519 * new key; @KSERR_NOKEYS@ if there are no suitable keys
520 * available. Also returns zero if there was insufficient
521 * buffer space (but the output buffer is broken in this case).
523 * Use: Encrypts a packet.
526 int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
528 time_t now = time(0);
529 keyset *ks = *ksroot;
533 T( trace(T_KEYSET, "keyset: no suitable keysets found"); )
535 return (KSERR_NOKEYS);
537 if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN))
542 return (doencrypt(ks, ty, b, bb));
545 /* --- @ksl_decrypt@ --- *
547 * Arguments: @keyset **ksroot@ = pointer to keyset list head
548 * @unsigned ty@ = expected type code
549 * @buf *b@ = pointer to input buffer
550 * @buf *bb@ = pointer to output buffer
552 * Returns: Zero on success; @KSERR_DECRYPT@ on failure. Also returns
553 * zero if there was insufficient buffer (but the output buffer
554 * is broken in this case).
556 * Use: Decrypts a packet.
559 int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb)
561 time_t now = time(0);
566 if (buf_ensure(bb, BLEN(b)))
569 for (ks = *ksroot; ks; ks = ks->next) {
572 if ((err = dodecrypt(ks, ty, b, bb, &seq)) == 0) {
573 if (ks->f & KSF_LISTEN) {
574 T( trace(T_KEYSET, "keyset: implicitly activating keyset %u",
576 ks->f &= ~KSF_LISTEN;
578 if (seq_check(&ks->iseq, seq, "SYMM"))
583 if (err != KSERR_DECRYPT) return (err);
585 T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); )
586 return (KSERR_DECRYPT);
589 /*----- That's all, folks -------------------------------------------------*/