| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * Handling of symmetric keysets |
| 4 | * |
| 5 | * (c) 2001 Straylight/Edgeware |
| 6 | */ |
| 7 | |
| 8 | /*----- Licensing notice --------------------------------------------------* |
| 9 | * |
| 10 | * This file is part of Trivial IP Encryption (TrIPE). |
| 11 | * |
| 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. |
| 16 | * |
| 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 |
| 20 | * for more details. |
| 21 | * |
| 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/>. |
| 24 | */ |
| 25 | |
| 26 | /*----- Header files ------------------------------------------------------*/ |
| 27 | |
| 28 | #include "tripe.h" |
| 29 | |
| 30 | /*----- Handy macros ------------------------------------------------------*/ |
| 31 | |
| 32 | #define KEYOK(ks, now) ((ks)->sz_exp > 0 && (ks)->t_exp > now) |
| 33 | |
| 34 | /*----- Low-level packet encryption and decryption ------------------------*/ |
| 35 | |
| 36 | /* --- Encrypted data format --- * |
| 37 | * |
| 38 | * Let %$p_i$% be the %$i$%-th plaintext message, with type %$t$%. We first |
| 39 | * compute |
| 40 | * |
| 41 | * %$c_i = \mathcal{E}\textrm{-CBC}_{K_{\text{E}}}(p_i)$% |
| 42 | * |
| 43 | * as the CBC-ciphertext of %$p_i$%, and then |
| 44 | * |
| 45 | * %$\sigma_i = \mathcal{T}_{K_{\text{M}}}(t, i, c_i)$% |
| 46 | * |
| 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]. |
| 51 | * |
| 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]. |
| 58 | */ |
| 59 | |
| 60 | /* --- @doencrypt@ --- * |
| 61 | * |
| 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 |
| 66 | * |
| 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. |
| 70 | * |
| 71 | * Use: Encrypts a message with the given key. We assume that the |
| 72 | * keyset is OK to use. |
| 73 | */ |
| 74 | |
| 75 | static int doencrypt(keyset *ks, unsigned ty, buf *b, buf *bb) |
| 76 | { |
| 77 | int rc; |
| 78 | size_t sz = BLEFT(b); |
| 79 | size_t osz, nsz; |
| 80 | |
| 81 | /* --- Initial tracing --- */ |
| 82 | |
| 83 | IF_TRACING(T_KEYSET, { |
| 84 | trace(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); |
| 88 | }) |
| 89 | |
| 90 | /* --- Apply the bulk-crypto transformation --- */ |
| 91 | |
| 92 | rc = ks->bulk->ops->encrypt(ks->bulk, ty, b, bb, ks->oseq); |
| 93 | if (rc || !BOK(bb)) return (rc); |
| 94 | ks->oseq++; |
| 95 | |
| 96 | /* --- Do the necessary accounting for data volume --- */ |
| 97 | |
| 98 | osz = ks->sz_exp; |
| 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); ) |
| 103 | rc = KSERR_REGEN; |
| 104 | } |
| 105 | ks->sz_exp = nsz; |
| 106 | |
| 107 | /* --- We're done --- */ |
| 108 | |
| 109 | return (rc); |
| 110 | } |
| 111 | |
| 112 | /* --- @dodecrypt@ --- * |
| 113 | * |
| 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 |
| 119 | * |
| 120 | * Returns: Zero on success; @KSERR_DECRYPT@ on failure. |
| 121 | * |
| 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@. |
| 128 | */ |
| 129 | |
| 130 | static int dodecrypt(keyset *ks, unsigned ty, buf *b, buf *bb, uint32 *seq) |
| 131 | { |
| 132 | const octet *q = BCUR(bb); |
| 133 | int rc; |
| 134 | |
| 135 | IF_TRACING(T_KEYSET, { |
| 136 | trace(T_KEYSET, |
| 137 | "keyset: try decrypting packet (type 0x%02x) using keyset %u", |
| 138 | ty, ks->seq); |
| 139 | trace_block(T_CRYPTO, "crypto: ciphertext packet", BCUR(b), BLEFT(b)); |
| 140 | }) |
| 141 | |
| 142 | rc = ks->bulk->ops->decrypt(ks->bulk, ty, b, bb, seq); |
| 143 | if (rc) return (rc); |
| 144 | |
| 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); |
| 149 | }) |
| 150 | return (0); |
| 151 | } |
| 152 | |
| 153 | /*----- Operations on a single keyset -------------------------------------*/ |
| 154 | |
| 155 | /* --- @ks_drop@ --- * |
| 156 | * |
| 157 | * Arguments: @keyset *ks@ = pointer to a keyset |
| 158 | * |
| 159 | * Returns: --- |
| 160 | * |
| 161 | * Use: Decrements a keyset's reference counter. If the counter hits |
| 162 | * zero, the keyset is freed. |
| 163 | */ |
| 164 | |
| 165 | void ks_drop(keyset *ks) |
| 166 | { |
| 167 | if (--ks->ref) return; |
| 168 | ks->bulk->ops->freectx(ks->bulk); |
| 169 | DESTROY(ks); |
| 170 | } |
| 171 | |
| 172 | /* --- @ks_derivekey@ --- * |
| 173 | * |
| 174 | * Arguments: @octet *k@ = pointer to an output buffer of at least |
| 175 | * @MAXHASHSZ@ bytes |
| 176 | * @size_t ksz@ = actual size wanted (for tracing) |
| 177 | * @const struct rawkey *rk@ = a raw key, as passed into |
| 178 | * @genkeys@ |
| 179 | * @int dir@ = direction for the key (@DIR_IN@ or @DIR_OUT@) |
| 180 | * @const char *what@ = label for the key (input to derivation) |
| 181 | * |
| 182 | * Returns: --- |
| 183 | * |
| 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. |
| 187 | */ |
| 188 | |
| 189 | struct rawkey { |
| 190 | const gchash *hc; |
| 191 | const octet *k; |
| 192 | size_t x, y, z; |
| 193 | }; |
| 194 | |
| 195 | void ks_derivekey(octet *k, size_t ksz, const struct rawkey *rk, |
| 196 | int dir, const char *what) |
| 197 | { |
| 198 | const gchash *hc = rk->hc; |
| 199 | ghash *h; |
| 200 | |
| 201 | assert(ksz <= hc->hashsz); |
| 202 | assert(hc->hashsz <= MAXHASHSZ); |
| 203 | h = GH_INIT(hc); |
| 204 | GH_HASH(h, "tripe-", 6); GH_HASH(h, what, strlen(what) + 1); |
| 205 | switch (dir) { |
| 206 | case DIR_IN: |
| 207 | GH_HASH(h, rk->k, rk->x); |
| 208 | GH_HASH(h, rk->k + rk->x, rk->y - rk->x); |
| 209 | break; |
| 210 | case DIR_OUT: |
| 211 | GH_HASH(h, rk->k + rk->x, rk->y - rk->x); |
| 212 | GH_HASH(h, rk->k, rk->x); |
| 213 | break; |
| 214 | default: |
| 215 | abort(); |
| 216 | } |
| 217 | GH_HASH(h, rk->k + rk->y, rk->z - rk->y); |
| 218 | GH_DONE(h, k); |
| 219 | GH_DESTROY(h); |
| 220 | IF_TRACING(T_KEYSET, { IF_TRACING(T_CRYPTO, { |
| 221 | char _buf[32]; |
| 222 | sprintf(_buf, "crypto: %s key %s", dir ? "outgoing" : "incoming", what); |
| 223 | trace_block(T_CRYPTO, _buf, k, ksz); |
| 224 | }) }) |
| 225 | } |
| 226 | |
| 227 | /* --- @ks_gen@ --- * |
| 228 | * |
| 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 |
| 232 | * |
| 233 | * Returns: A pointer to the new keyset. |
| 234 | * |
| 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. |
| 243 | * |
| 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. |
| 247 | */ |
| 248 | |
| 249 | keyset *ks_gen(const void *k, size_t x, size_t y, size_t z, peer *p) |
| 250 | { |
| 251 | keyset *ks = CREATE(keyset); |
| 252 | time_t now = time(0); |
| 253 | const algswitch *algs = &p->kx.kpriv->algs; |
| 254 | struct rawkey rk; |
| 255 | T( static unsigned seq = 0; ) |
| 256 | |
| 257 | T( trace(T_KEYSET, "keyset: adding new keyset %u", seq); ) |
| 258 | |
| 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; |
| 262 | |
| 263 | T( ks->seq = seq++; ) |
| 264 | ks->ref = 1; |
| 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; |
| 268 | ks->oseq = 0; |
| 269 | seq_reset(&ks->iseq); |
| 270 | ks->next = 0; |
| 271 | ks->p = p; |
| 272 | ks->f = KSF_LISTEN; |
| 273 | return (ks); |
| 274 | } |
| 275 | |
| 276 | /* --- @ks_activate@ --- * |
| 277 | * |
| 278 | * Arguments: @keyset *ks@ = pointer to a keyset |
| 279 | * |
| 280 | * Returns: --- |
| 281 | * |
| 282 | * Use: Activates a keyset, so that it can be used for encrypting |
| 283 | * outgoing messages. |
| 284 | */ |
| 285 | |
| 286 | void ks_activate(keyset *ks) |
| 287 | { |
| 288 | if (ks->f & KSF_LISTEN) { |
| 289 | T( trace(T_KEYSET, "keyset: activating keyset %u", ks->seq); ) |
| 290 | ks->f &= ~KSF_LISTEN; |
| 291 | } |
| 292 | } |
| 293 | |
| 294 | /* --- @ks_encrypt@ --- * |
| 295 | * |
| 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 |
| 300 | * |
| 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). |
| 305 | * |
| 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. |
| 310 | * |
| 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 |
| 315 | */ |
| 316 | |
| 317 | int ks_encrypt(keyset *ks, unsigned ty, buf *b, buf *bb) |
| 318 | { |
| 319 | time_t now = time(0); |
| 320 | |
| 321 | if (!KEYOK(ks, now)) { |
| 322 | buf_break(bb); |
| 323 | return (KSERR_NOKEYS); |
| 324 | } |
| 325 | return (doencrypt(ks, ty, b, bb)); |
| 326 | } |
| 327 | |
| 328 | /* --- @ks_decrypt@ --- * |
| 329 | * |
| 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 |
| 334 | * |
| 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). |
| 338 | * |
| 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. |
| 342 | * |
| 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 |
| 347 | */ |
| 348 | |
| 349 | int ks_decrypt(keyset *ks, unsigned ty, buf *b, buf *bb) |
| 350 | { |
| 351 | time_t now = time(0); |
| 352 | uint32 seq; |
| 353 | int err; |
| 354 | |
| 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); |
| 359 | return (0); |
| 360 | } |
| 361 | |
| 362 | /*----- Keyset list handling ----------------------------------------------*/ |
| 363 | |
| 364 | /* --- @ksl_free@ --- * |
| 365 | * |
| 366 | * Arguments: @keyset **ksroot@ = pointer to keyset list head |
| 367 | * |
| 368 | * Returns: --- |
| 369 | * |
| 370 | * Use: Frees (releases references to) all of the keys in a keyset. |
| 371 | */ |
| 372 | |
| 373 | void ksl_free(keyset **ksroot) |
| 374 | { |
| 375 | keyset *ks, *ksn; |
| 376 | for (ks = *ksroot; ks; ks = ksn) { |
| 377 | ksn = ks->next; |
| 378 | ks->f &= ~KSF_LINK; |
| 379 | ks_drop(ks); |
| 380 | } |
| 381 | } |
| 382 | |
| 383 | /* --- @ksl_link@ --- * |
| 384 | * |
| 385 | * Arguments: @keyset **ksroot@ = pointer to keyset list head |
| 386 | * @keyset *ks@ = pointer to a keyset |
| 387 | * |
| 388 | * Returns: --- |
| 389 | * |
| 390 | * Use: Links a keyset into a list. A keyset can only be on one list |
| 391 | * at a time. Bad things happen otherwise. |
| 392 | */ |
| 393 | |
| 394 | void ksl_link(keyset **ksroot, keyset *ks) |
| 395 | { |
| 396 | assert(!(ks->f & KSF_LINK)); |
| 397 | ks->next = *ksroot; |
| 398 | *ksroot = ks; |
| 399 | ks->f |= KSF_LINK; |
| 400 | ks->ref++; |
| 401 | } |
| 402 | |
| 403 | /* --- @ksl_prune@ --- * |
| 404 | * |
| 405 | * Arguments: @keyset **ksroot@ = pointer to keyset list head |
| 406 | * |
| 407 | * Returns: --- |
| 408 | * |
| 409 | * Use: Prunes the keyset list by removing keys which mustn't be used |
| 410 | * any more. |
| 411 | */ |
| 412 | |
| 413 | void ksl_prune(keyset **ksroot) |
| 414 | { |
| 415 | time_t now = time(0); |
| 416 | |
| 417 | while (*ksroot) { |
| 418 | keyset *ks = *ksroot; |
| 419 | |
| 420 | if (ks->t_exp <= now) { |
| 421 | T( trace(T_KEYSET, "keyset: expiring keyset %u (time limit reached)", |
| 422 | ks->seq); ) |
| 423 | goto kill; |
| 424 | } else if (ks->sz_exp == 0) { |
| 425 | T( trace(T_KEYSET, "keyset: expiring keyset %u (data limit reached)", |
| 426 | ks->seq); ) |
| 427 | goto kill; |
| 428 | } else { |
| 429 | ksroot = &ks->next; |
| 430 | continue; |
| 431 | } |
| 432 | |
| 433 | kill: |
| 434 | *ksroot = ks->next; |
| 435 | ks->f &= ~KSF_LINK; |
| 436 | ks_drop(ks); |
| 437 | } |
| 438 | } |
| 439 | |
| 440 | /* --- @ksl_encrypt@ --- * |
| 441 | * |
| 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 |
| 446 | * |
| 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). |
| 451 | * |
| 452 | * Use: Encrypts a packet. |
| 453 | */ |
| 454 | |
| 455 | int ksl_encrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb) |
| 456 | { |
| 457 | time_t now = time(0); |
| 458 | keyset *ks = *ksroot; |
| 459 | |
| 460 | for (;;) { |
| 461 | if (!ks) { |
| 462 | T( trace(T_KEYSET, "keyset: no suitable keysets found"); ) |
| 463 | buf_break(bb); |
| 464 | return (KSERR_NOKEYS); |
| 465 | } |
| 466 | if (KEYOK(ks, now) && !(ks->f & KSF_LISTEN)) |
| 467 | break; |
| 468 | ks = ks->next; |
| 469 | } |
| 470 | |
| 471 | return (doencrypt(ks, ty, b, bb)); |
| 472 | } |
| 473 | |
| 474 | /* --- @ksl_decrypt@ --- * |
| 475 | * |
| 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 |
| 480 | * |
| 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). |
| 484 | * |
| 485 | * Use: Decrypts a packet. |
| 486 | */ |
| 487 | |
| 488 | int ksl_decrypt(keyset **ksroot, unsigned ty, buf *b, buf *bb) |
| 489 | { |
| 490 | time_t now = time(0); |
| 491 | keyset *ks; |
| 492 | uint32 seq; |
| 493 | int err; |
| 494 | |
| 495 | if (buf_ensure(bb, BLEN(b))) |
| 496 | return (0); |
| 497 | |
| 498 | for (ks = *ksroot; ks; ks = ks->next) { |
| 499 | if (!KEYOK(ks, now)) |
| 500 | continue; |
| 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", |
| 504 | ks->seq); ) |
| 505 | ks->f &= ~KSF_LISTEN; |
| 506 | } |
| 507 | if (seq_check(&ks->iseq, seq, "SYMM")) |
| 508 | return (KSERR_SEQ); |
| 509 | else |
| 510 | return (0); |
| 511 | } |
| 512 | if (err != KSERR_DECRYPT) return (err); |
| 513 | } |
| 514 | T( trace(T_KEYSET, "keyset: no matching keys, or incorrect MAC"); ) |
| 515 | return (KSERR_DECRYPT); |
| 516 | } |
| 517 | |
| 518 | /*----- That's all, folks -------------------------------------------------*/ |