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 /*----- Tunable parameters ------------------------------------------------*/
33 /* --- Note on size limits --- *
35 * For a 64-bit block cipher (e.g., Blowfish), the probability of a collision
36 * occurring after 32 MB is less than %$2^{-21}$%, and the probability of a
37 * collision occurring after 64 MB is less than %$2^{-19}$%. These could be
38 * adjusted dependent on the encryption scheme, but it's too much pain.
41 #define T_EXP MIN(60) /* Expiry time for a key */
42 #define T_REGEN MIN(45) /* Regeneration time for a key */
43 #define SZ_EXP MEG(64) /* Expiry data size for a key */
44 #define SZ_REGEN MEG(32) /* Data size threshold for regen */
46 /*----- Handy macros ------------------------------------------------------*/
48 #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now)
50 #define SEQSZ 4 /* Size of sequence number packet */
52 /*----- Low-level packet encryption and decryption ------------------------*/
54 /* --- Encrypted data format --- *
56 * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first
59 * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$%
61 * as the CBC-ciphertext of %$p_i$%, and then
63 * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$%
65 * as a MAC on the %%\emph{ciphertext}%%. The message sent is then the pair
66 * %$(\sigma_i, c_i)$%. This construction is provably secure in the NM-CCA
67 * sense (assuming that the cipher is IND-CPA, and the MAC is SUF-CMA)
68 * [Bellare and Namprempre].
70 * This also ensures that, assuming the key is good, we have a secure channel
71 * [Krawczyk]. Actually, [Krawczyk] shows that, if the cipher is either a
72 * simple stream cipher or a block cipher in CBC mode, we can use the MAC-
73 * then-encrypt scheme and still have a secure channel. However, I like the
74 * NM-CCA guarantee from [Bellare and Namprempre]. I'm less worried about
75 * the Horton Principle [Wagner and Schneier].
78 /* --- @doencrypt@ --- *
80 * Arguments: @keyset *ks@ = pointer to keyset to use
81 * @unsigned ty@ = type of message this is
82 * @buf *b@ = pointer to an input buffer
83 * @buf *bb@ = pointer to an output buffer
85 * Returns: Zero if OK; @KSERR_REGEN@ if it's time to generate new keys.
86 * Also returns zero if there was insufficient buffer space, but
87 * the buffer is broken in this case.
89 * Use: Encrypts a message with the given key. We assume that the
90 * keyset is OK to use.
93 static int doencrypt(keyset
*ks
, unsigned ty
, buf
*b
, buf
*bb
)
96 gcipher
*c
= ks
->cout
;
97 const octet
*p
= BCUR(b
);
99 octet
*qmac
, *qseq
, *qiv
, *qpk
;
101 size_t ivsz
= GC_CLASS(c
)->blksz
;
102 size_t tagsz
= ks
->tagsz
;
107 /* --- Allocate the required buffer space --- */
109 if (buf_ensure(bb
, tagsz
+ SEQSZ
+ ivsz
+ sz
))
110 return (0); /* Caution! */
111 qmac
= BCUR(bb
); qseq
= qmac
+ tagsz
; qiv
= qseq
+ SEQSZ
; qpk
= qiv
+ ivsz
;
112 BSTEP(bb
, tagsz
+ SEQSZ
+ ivsz
+ sz
);
115 oseq
= ks
->oseq
++; STORE32(qseq
, oseq
);
116 IF_TRACING(T_KEYSET
, {
117 trace(T_KEYSET
, "keyset: encrypting packet %lu using keyset %u",
118 (unsigned long)oseq
, ks
->seq
);
119 trace_block(T_CRYPTO
, "crypto: plaintext packet", p
, sz
);
122 /* --- Encrypt the packet --- */
125 rand_get(RAND_GLOBAL
, qiv
, ivsz
);
127 IF_TRACING(T_KEYSET
, {
128 trace_block(T_CRYPTO
, "crypto: initialization vector", qiv
, ivsz
);
131 GC_ENCRYPT(c
, p
, qpk
, sz
);
132 IF_TRACING(T_KEYSET
, {
133 trace_block(T_CRYPTO
, "crypto: encrypted packet", qpk
, sz
);
136 /* --- Now compute the MAC --- */
139 h
= GM_INIT(ks
->mout
);
140 GH_HASH(h
, t
, sizeof(t
));
141 GH_HASH(h
, qseq
, SEQSZ
+ ivsz
+ sz
);
142 memcpy(qmac
, GH_DONE(h
, 0), tagsz
);
144 IF_TRACING(T_KEYSET
, {
145 trace_block(T_CRYPTO
, "crypto: computed MAC", qmac
, tagsz
);
149 /* --- Deduct the packet size from the key's data life --- */
156 if (osz
>= SZ_REGEN
&& nsz
< SZ_REGEN
) {
157 T( trace(T_KEYSET
, "keyset: keyset %u data regen limit exceeded -- "
158 "forcing exchange", ks
->seq
); )
165 /* --- @dodecrypt@ --- *
167 * Arguments: @keyset *ks@ = pointer to keyset to use
168 * @unsigned ty@ = expected type code
169 * @buf *b@ = pointer to an input buffer
170 * @buf *bb@ = pointer to an output buffer
171 * @uint32 *seq@ = where to store the sequence number
173 * Returns: Zero on success; @KSERR_DECRYPT@ on failure.
175 * Use: Attempts to decrypt a message with the given key. No other
176 * checking (e.g., sequence number checks) is performed. We
177 * assume that the keyset is OK to use, and that there is
178 * sufficient output buffer space reserved. If the decryption
179 * is successful, the buffer pointer is moved past the decrypted
180 * packet, and the packet's sequence number is stored in @*seq@.
183 static int dodecrypt(keyset
*ks
, unsigned ty
, buf
*b
, buf
*bb
, uint32
*seq
)
185 const octet
*pmac
, *piv
, *pseq
, *ppk
;
186 size_t psz
= BLEFT(b
);
190 gcipher
*c
= ks
->cin
;
191 size_t ivsz
= GC_CLASS(c
)->blksz
;
192 size_t tagsz
= ks
->tagsz
;
197 /* --- Break up the packet into its components --- */
199 if (psz
< ivsz
+ SEQSZ
+ tagsz
) {
200 T( trace(T_KEYSET
, "keyset: block too small for keyset %u", ks
->seq
); )
201 return (KSERR_DECRYPT
);
203 sz
= psz
- ivsz
- SEQSZ
- tagsz
;
204 pmac
= BCUR(b
); pseq
= pmac
+ tagsz
; piv
= pseq
+ SEQSZ
; ppk
= piv
+ ivsz
;
207 IF_TRACING(T_KEYSET
, {
208 trace(T_KEYSET
, "keyset: decrypting using keyset %u", ks
->seq
);
209 trace_block(T_CRYPTO
, "crypto: ciphertext packet", ppk
, sz
);
212 /* --- Verify the MAC on the packet --- */
215 h
= GM_INIT(ks
->min
);
216 GH_HASH(h
, t
, sizeof(t
));
217 GH_HASH(h
, pseq
, SEQSZ
+ ivsz
+ sz
);
219 eq
= !memcmp(mac
, pmac
, tagsz
);
220 IF_TRACING(T_KEYSET
, {
221 trace_block(T_CRYPTO
, "crypto: computed MAC", mac
, tagsz
);
225 IF_TRACING(T_KEYSET
, {
226 trace(T_KEYSET
, "keyset: incorrect MAC: decryption failed");
227 trace_block(T_CRYPTO
, "crypto: expected MAC", pmac
, tagsz
);
229 return (KSERR_DECRYPT
);
233 /* --- Decrypt the packet --- */
237 IF_TRACING(T_KEYSET
, {
238 trace_block(T_CRYPTO
, "crypto: initialization vector", piv
, ivsz
);
241 GC_DECRYPT(c
, ppk
, q
, sz
);
244 IF_TRACING(T_KEYSET
, {
245 trace(T_KEYSET
, "keyset: decrypted OK (sequence = %lu)",
246 (unsigned long)LOAD32(pseq
));
247 trace_block(T_CRYPTO
, "crypto: decrypted packet", q
, sz
);
253 /*----- Operations on a single keyset -------------------------------------*/
255 /* --- @ks_drop@ --- *
257 * Arguments: @keyset *ks@ = pointer to a keyset
261 * Use: Decrements a keyset's reference counter. If the counter hits
262 * zero, the keyset is freed.
265 void ks_drop(keyset
*ks
)
270 GC_DESTROY(ks
->cout
);
272 GM_DESTROY(ks
->mout
);
276 /* --- @ks_gen@ --- *
278 * Arguments: @const void *k@ = pointer to key material
279 * @size_t x, y, z@ = offsets into key material (see below)
280 * @peer *p@ = pointer to peer information
282 * Returns: A pointer to the new keyset.
284 * Use: Derives a new keyset from the given key material. The
285 * offsets @x@, @y@ and @z@ separate the key material into three
286 * parts. Between the @k@ and @k + x@ is `my' contribution to
287 * the key material; between @k + x@ and @k + y@ is `your'
288 * contribution; and between @k + y@ and @k + z@ is a shared
289 * value we made together. These are used to construct two
290 * pairs of symmetric keys. Each pair consists of an encryption
291 * key and a message authentication key. One pair is used for
292 * outgoing messages, the other for incoming messages.
294 * The new key is marked so that it won't be selected for output
295 * by @ksl_encrypt@. You can still encrypt data with it by
296 * calling @ks_encrypt@ directly.
299 keyset
*ks_gen(const void *k
, size_t x
, size_t y
, size_t z
, peer
*p
)
303 keyset
*ks
= CREATE(keyset
);
304 time_t now
= time(0);
306 T( static unsigned seq
= 0; )
308 T( trace(T_KEYSET
, "keyset: adding new keyset %u", seq
); )
310 /* --- Construct the various keys --- *
312 * This is done with macros, because it's quite tedious.
315 #define MINE GH_HASH(h, pp, x)
316 #define YOURS GH_HASH(h, pp + x, y - x)
317 #define OURS GH_HASH(h, pp + y, z - y)
319 #define HASH_in MINE; YOURS; OURS
320 #define HASH_out YOURS; MINE; OURS
321 #define INIT_c(k) GC_INIT(algs.c, (k), algs.cksz)
322 #define INIT_m(k) GM_KEY(algs.m, (k), algs.mksz)
323 #define STR_c "encryption"
324 #define STR_m "integrity"
325 #define STR_in "incoming"
326 #define STR_out "outgoing"
328 #define SETKEY(a, dir) do { \
329 h = GH_INIT(algs.h); \
330 HASH_STRING(h, "tripe-" STR_##a); \
332 hh = GH_DONE(h, 0); \
333 IF_TRACING(T_KEYSET, { \
334 trace_block(T_CRYPTO, "crypto: " STR_##dir " key " STR_##a, \
337 ks->a##dir = INIT_##a(hh); \
341 SETKEY(c
, in
); SETKEY(c
, out
);
342 SETKEY(m
, in
); SETKEY(m
, out
);
357 T( ks
->seq
= seq
++; )
359 ks
->t_exp
= now
+ T_EXP
;
362 seq_reset(&ks
->iseq
);
366 ks
->tagsz
= algs
.tagsz
;
370 /* --- @ks_tregen@ --- *
372 * Arguments: @keyset *ks@ = pointer to a keyset
374 * Returns: The time at which moves ought to be made to replace this key.
377 time_t ks_tregen(keyset
*ks
) { return (ks
->t_exp
- T_EXP
+ T_REGEN
); }
379 /* --- @ks_activate@ --- *
381 * Arguments: @keyset *ks@ = pointer to a keyset
385 * Use: Activates a keyset, so that it can be used for encrypting
389 void ks_activate(keyset
*ks
)
391 if (ks
->f
& KSF_LISTEN
) {
392 T( trace(T_KEYSET
, "keyset: activating keyset %u", ks
->seq
); )
393 ks
->f
&= ~KSF_LISTEN
;
397 /* --- @ks_encrypt@ --- *
399 * Arguments: @keyset *ks@ = pointer to a keyset
400 * @unsigned ty@ = message type
401 * @buf *b@ = pointer to input buffer
402 * @buf *bb@ = pointer to output buffer
404 * Returns: Zero if successful; @KSERR_REGEN@ if we should negotiate a
405 * new key; @KSERR_NOKEYS@ if the key is not usable. Also
406 * returns zero if there was insufficient buffer (but the output
407 * buffer is broken in this case).
409 * Use: Encrypts a block of data using the key. Note that the `key
410 * ought to be replaced' notification is only ever given once
411 * for each key. Also note that this call forces a keyset to be
412 * used even if it's marked as not for data output.
415 int ks_encrypt(keyset
*ks
, unsigned ty
, buf
*b
, buf
*bb
)
417 time_t now
= time(0);
419 if (!KEYOK(ks
, now
)) {
421 return (KSERR_NOKEYS
);
423 return (doencrypt(ks
, ty
, b
, bb
));
426 /* --- @ks_decrypt@ --- *
428 * Arguments: @keyset *ks@ = pointer to a keyset
429 * @unsigned ty@ = expected type code
430 * @buf *b@ = pointer to an input buffer
431 * @buf *bb@ = pointer to an output buffer
433 * Returns: Zero on success; @KSERR_DECRYPT@ on failure. Also returns
434 * zero if there was insufficient buffer (but the output buffer
435 * is broken in this case).
437 * Use: Attempts to decrypt a message using a given key. Note that
438 * requesting decryption with a key directly won't clear a
439 * marking that it's not for encryption.
442 int ks_decrypt(keyset
*ks
, unsigned ty
, buf
*b
, buf
*bb
)
444 time_t now
= time(0);
447 if (!KEYOK(ks
, now
) ||
448 buf_ensure(bb
, BLEN(b
)) ||
449 dodecrypt(ks
, ty
, b
, bb
, &seq
) ||
450 seq_check(&ks
->iseq
, seq
, "SYMM"))
451 return (KSERR_DECRYPT
);
455 /*----- Keyset list handling ----------------------------------------------*/
457 /* --- @ksl_free@ --- *
459 * Arguments: @keyset **ksroot@ = pointer to keyset list head
463 * Use: Frees (releases references to) all of the keys in a keyset.
466 void ksl_free(keyset
**ksroot
)
469 for (ks
= *ksroot
; ks
; ks
= ksn
) {
476 /* --- @ksl_link@ --- *
478 * Arguments: @keyset **ksroot@ = pointer to keyset list head
479 * @keyset *ks@ = pointer to a keyset
483 * Use: Links a keyset into a list. A keyset can only be on one list
484 * at a time. Bad things happen otherwise.
487 void ksl_link(keyset
**ksroot
, keyset
*ks
)
489 assert(!(ks
->f
& KSF_LINK
));
496 /* --- @ksl_prune@ --- *
498 * Arguments: @keyset **ksroot@ = pointer to keyset list head
502 * Use: Prunes the keyset list by removing keys which mustn't be used
506 void ksl_prune(keyset
**ksroot
)
508 time_t now
= time(0);
511 keyset
*ks
= *ksroot
;
513 if (ks
->t_exp
<= now
) {
514 T( trace(T_KEYSET
, "keyset: expiring keyset %u (time limit reached)",
517 } else if (ks
->sz_exp
== 0) {
518 T( trace(T_KEYSET
, "keyset: expiring keyset %u (data limit reached)",
533 /* --- @ksl_encrypt@ --- *
535 * Arguments: @keyset **ksroot@ = pointer to keyset list head
536 * @unsigned ty@ = message type
537 * @buf *b@ = pointer to input buffer
538 * @buf *bb@ = pointer to output buffer
540 * Returns: Zero if successful; @KSERR_REGEN@ if it's time to negotiate a
541 * new key; @KSERR_NOKEYS@ if there are no suitable keys
542 * available. Also returns zero if there was insufficient
543 * buffer space (but the output buffer is broken in this case).
545 * Use: Encrypts a packet.
548 int ksl_encrypt(keyset
**ksroot
, unsigned ty
, buf
*b
, buf
*bb
)
550 time_t now
= time(0);
551 keyset
*ks
= *ksroot
;
555 T( trace(T_KEYSET
, "keyset: no suitable keysets found"); )
557 return (KSERR_NOKEYS
);
559 if (KEYOK(ks
, now
) && !(ks
->f
& KSF_LISTEN
))
564 return (doencrypt(ks
, ty
, b
, bb
));
567 /* --- @ksl_decrypt@ --- *
569 * Arguments: @keyset **ksroot@ = pointer to keyset list head
570 * @unsigned ty@ = expected type code
571 * @buf *b@ = pointer to input buffer
572 * @buf *bb@ = pointer to output buffer
574 * Returns: Zero on success; @KSERR_DECRYPT@ on failure. Also returns
575 * zero if there was insufficient buffer (but the output buffer
576 * is broken in this case).
578 * Use: Decrypts a packet.
581 int ksl_decrypt(keyset
**ksroot
, unsigned ty
, buf
*b
, buf
*bb
)
583 time_t now
= time(0);
587 if (buf_ensure(bb
, BLEN(b
)))
588 return (KSERR_DECRYPT
);
590 for (ks
= *ksroot
; ks
; ks
= ks
->next
) {
593 if (!dodecrypt(ks
, ty
, b
, bb
, &seq
)) {
594 if (ks
->f
& KSF_LISTEN
) {
595 T( trace(T_KEYSET
, "keyset: implicitly activating keyset %u",
597 ks
->f
&= ~KSF_LISTEN
;
599 if (seq_check(&ks
->iseq
, seq
, "SYMM"))
600 return (KSERR_DECRYPT
);
605 T( trace(T_KEYSET
, "keyset: no matching keys, or incorrect MAC"); )
606 return (KSERR_DECRYPT
);
609 /*----- That's all, folks -------------------------------------------------*/