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_derivekey@ --- *
174 * Arguments: @octet *k@ = pointer to an output buffer of at least
176 * @size_t ksz@ = actual size wanted (for tracing)
177 * @const struct rawkey *rk@ = a raw key, as passed into
179 * @int dir@ = direction for the key (@DIR_IN@ or @DIR_OUT@)
180 * @const char *what@ = label for the key (input to derivation)
184 * Use: Derives a session key, for use on incoming or outgoing data.
185 * This function is part of a private protocol between @ks_gen@
186 * and the bulk crypto transform @genkeys@ operation.
195 void ks_derivekey(octet
*k
, size_t ksz
, const struct rawkey
*rk
,
196 int dir
, const char *what
)
198 const gchash
*hc
= rk
->hc
;
201 assert(ksz
<= hc
->hashsz
);
202 assert(hc
->hashsz
<= MAXHASHSZ
);
204 GH_HASH(h
, "tripe-", 6); GH_HASH(h
, what
, strlen(what
) + 1);
207 GH_HASH(h
, rk
->k
, rk
->x
);
208 GH_HASH(h
, rk
->k
+ rk
->x
, rk
->y
- rk
->x
);
211 GH_HASH(h
, rk
->k
+ rk
->x
, rk
->y
- rk
->x
);
212 GH_HASH(h
, rk
->k
, rk
->x
);
217 GH_HASH(h
, rk
->k
+ rk
->y
, rk
->z
- rk
->y
);
220 IF_TRACING(T_KEYSET
, { IF_TRACING(T_CRYPTO
, {
222 sprintf(_buf
, "crypto: %s key %s", dir ?
"outgoing" : "incoming", what
);
223 trace_block(T_CRYPTO
, _buf
, k
, ksz
);
227 /* --- @ks_gen@ --- *
229 * Arguments: @const void *k@ = pointer to key material
230 * @size_t x, y, z@ = offsets into key material (see below)
231 * @peer *p@ = pointer to peer information
233 * Returns: A pointer to the new keyset.
235 * Use: Derives a new keyset from the given key material. The
236 * offsets @x@, @y@ and @z@ separate the key material into three
237 * parts. Between the @k@ and @k + x@ is `my' contribution to
238 * the key material; between @k + x@ and @k + y@ is `your'
239 * contribution; and between @k + y@ and @k + z@ is a shared
240 * value we made together. These are used to construct two
241 * collections of symmetric keys: one for outgoing messages, the
242 * other for incoming messages.
244 * The new key is marked so that it won't be selected for output
245 * by @ksl_encrypt@. You can still encrypt data with it by
246 * calling @ks_encrypt@ directly.
249 keyset
*ks_gen(const void *k
, size_t x
, size_t y
, size_t z
, peer
*p
)
251 keyset
*ks
= CREATE(keyset
);
252 time_t now
= time(0);
253 const algswitch
*algs
= &p
->kx
.kpriv
->algs
;
255 T( static unsigned seq
= 0; )
257 T( trace(T_KEYSET
, "keyset: adding new keyset %u", seq
); )
259 rk
.hc
= algs
->h
; rk
.k
= k
; rk
.x
= x
; rk
.y
= y
; rk
.z
= z
;
260 ks
->bulk
= algs
->bulk
->ops
->genkeys(algs
->bulk
, &rk
);
261 ks
->bulk
->ops
= algs
->bulk
->ops
;
263 T( ks
->seq
= seq
++; )
265 ks
->t_exp
= now
+ T_EXP
;
266 ks
->sz_exp
= algs
->bulk
->ops
->expsz(algs
->bulk
);
267 ks
->sz_regen
= ks
->sz_exp
/2;
269 seq_reset(&ks
->iseq
);
276 /* --- @ks_activate@ --- *
278 * Arguments: @keyset *ks@ = pointer to a keyset
282 * Use: Activates a keyset, so that it can be used for encrypting
286 void ks_activate(keyset
*ks
)
288 if (ks
->f
& KSF_LISTEN
) {
289 T( trace(T_KEYSET
, "keyset: activating keyset %u", ks
->seq
); )
290 ks
->f
&= ~KSF_LISTEN
;
294 /* --- @ks_encrypt@ --- *
296 * Arguments: @keyset *ks@ = pointer to a keyset
297 * @unsigned ty@ = message type
298 * @buf *b@ = pointer to input buffer
299 * @buf *bb@ = pointer to output buffer
301 * Returns: Zero if successful; @KSERR_REGEN@ if we should negotiate a
302 * new key; @KSERR_NOKEYS@ if the key is not usable. Also
303 * returns zero if there was insufficient buffer (but the output
304 * buffer is broken in this case).
306 * Use: Encrypts a block of data using the key. Note that the `key
307 * ought to be replaced' notification is only ever given once
308 * for each key. Also note that this call forces a keyset to be
309 * used even if it's marked as not for data output.
311 * The encryption transform is permitted to corrupt @buf_u@ for
312 * its own purposes. Neither the source nor destination should
313 * be within @buf_u@; and callers mustn't expect anything stored
314 * in @buf_u@ to still
317 int ks_encrypt(keyset
*ks
, unsigned ty
, buf
*b
, buf
*bb
)
319 time_t now
= time(0);
321 if (!KEYOK(ks
, now
)) {
323 return (KSERR_NOKEYS
);
325 return (doencrypt(ks
, ty
, b
, bb
));
328 /* --- @ks_decrypt@ --- *
330 * Arguments: @keyset *ks@ = pointer to a keyset
331 * @unsigned ty@ = expected type code
332 * @buf *b@ = pointer to an input buffer
333 * @buf *bb@ = pointer to an output buffer
335 * Returns: Zero on success; @KSERR_...@ on failure. Also returns
336 * zero if there was insufficient buffer (but the output buffer
337 * is broken in this case).
339 * Use: Attempts to decrypt a message using a given key. Note that
340 * requesting decryption with a key directly won't clear a
341 * marking that it's not for encryption.
343 * The decryption transform is permitted to corrupt @buf_u@ for
344 * its own purposes. Neither the source nor destination should
345 * be within @buf_u@; and callers mustn't expect anything stored
346 * in @buf_u@ to still
349 int ks_decrypt(keyset
*ks
, unsigned ty
, buf
*b
, buf
*bb
)
351 time_t now
= time(0);
355 if (!KEYOK(ks
, now
)) return (KSERR_DECRYPT
);
356 if (buf_ensure(bb
, BLEN(b
))) return (0);
357 if ((err
= dodecrypt(ks
, ty
, b
, bb
, &seq
)) != 0) return (err
);
358 if (seq_check(&ks
->iseq
, seq
, "SYMM")) return (KSERR_SEQ
);
362 /*----- Keyset list handling ----------------------------------------------*/
364 /* --- @ksl_free@ --- *
366 * Arguments: @keyset **ksroot@ = pointer to keyset list head
370 * Use: Frees (releases references to) all of the keys in a keyset.
373 void ksl_free(keyset
**ksroot
)
376 for (ks
= *ksroot
; ks
; ks
= ksn
) {
383 /* --- @ksl_link@ --- *
385 * Arguments: @keyset **ksroot@ = pointer to keyset list head
386 * @keyset *ks@ = pointer to a keyset
390 * Use: Links a keyset into a list. A keyset can only be on one list
391 * at a time. Bad things happen otherwise.
394 void ksl_link(keyset
**ksroot
, keyset
*ks
)
396 assert(!(ks
->f
& KSF_LINK
));
403 /* --- @ksl_prune@ --- *
405 * Arguments: @keyset **ksroot@ = pointer to keyset list head
409 * Use: Prunes the keyset list by removing keys which mustn't be used
413 void ksl_prune(keyset
**ksroot
)
415 time_t now
= time(0);
418 keyset
*ks
= *ksroot
;
420 if (ks
->t_exp
<= now
) {
421 T( trace(T_KEYSET
, "keyset: expiring keyset %u (time limit reached)",
424 } else if (ks
->sz_exp
== 0) {
425 T( trace(T_KEYSET
, "keyset: expiring keyset %u (data limit reached)",
440 /* --- @ksl_encrypt@ --- *
442 * Arguments: @keyset **ksroot@ = pointer to keyset list head
443 * @unsigned ty@ = message type
444 * @buf *b@ = pointer to input buffer
445 * @buf *bb@ = pointer to output buffer
447 * Returns: Zero if successful; @KSERR_REGEN@ if it's time to negotiate a
448 * new key; @KSERR_NOKEYS@ if there are no suitable keys
449 * available. Also returns zero if there was insufficient
450 * buffer space (but the output buffer is broken in this case).
452 * Use: Encrypts a packet.
455 int ksl_encrypt(keyset
**ksroot
, unsigned ty
, buf
*b
, buf
*bb
)
457 time_t now
= time(0);
458 keyset
*ks
= *ksroot
;
462 T( trace(T_KEYSET
, "keyset: no suitable keysets found"); )
464 return (KSERR_NOKEYS
);
466 if (KEYOK(ks
, now
) && !(ks
->f
& KSF_LISTEN
))
471 return (doencrypt(ks
, ty
, b
, bb
));
474 /* --- @ksl_decrypt@ --- *
476 * Arguments: @keyset **ksroot@ = pointer to keyset list head
477 * @unsigned ty@ = expected type code
478 * @buf *b@ = pointer to input buffer
479 * @buf *bb@ = pointer to output buffer
481 * Returns: Zero on success; @KSERR_DECRYPT@ on failure. Also returns
482 * zero if there was insufficient buffer (but the output buffer
483 * is broken in this case).
485 * Use: Decrypts a packet.
488 int ksl_decrypt(keyset
**ksroot
, unsigned ty
, buf
*b
, buf
*bb
)
490 time_t now
= time(0);
495 if (buf_ensure(bb
, BLEN(b
)))
498 for (ks
= *ksroot
; ks
; ks
= ks
->next
) {
501 if ((err
= dodecrypt(ks
, ty
, b
, bb
, &seq
)) == 0) {
502 if (ks
->f
& KSF_LISTEN
) {
503 T( trace(T_KEYSET
, "keyset: implicitly activating keyset %u",
505 ks
->f
&= ~KSF_LISTEN
;
507 if (seq_check(&ks
->iseq
, seq
, "SYMM"))
512 if (err
!= KSERR_DECRYPT
) return (err
);
514 T( trace(T_KEYSET
, "keyset: no matching keys, or incorrect MAC"); )
515 return (KSERR_DECRYPT
);
518 /*----- That's all, folks -------------------------------------------------*/