| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: keyexch.c,v 1.2 2001/02/16 21:24:27 mdw Exp $ |
| 4 | * |
| 5 | * Key exchange protocol |
| 6 | * |
| 7 | * (c) 2001 Straylight/Edgeware |
| 8 | */ |
| 9 | |
| 10 | /*----- Licensing notice --------------------------------------------------* |
| 11 | * |
| 12 | * This file is part of Trivial IP Encryption (TrIPE). |
| 13 | * |
| 14 | * TrIPE is free software; you can redistribute it and/or modify |
| 15 | * it under the terms of the GNU General Public License as published by |
| 16 | * the Free Software Foundation; either version 2 of the License, or |
| 17 | * (at your option) any later version. |
| 18 | * |
| 19 | * TrIPE is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 22 | * GNU General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU General Public License |
| 25 | * along with TrIPE; if not, write to the Free Software Foundation, |
| 26 | * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| 27 | */ |
| 28 | |
| 29 | /*----- Revision history --------------------------------------------------* |
| 30 | * |
| 31 | * $Log: keyexch.c,v $ |
| 32 | * Revision 1.2 2001/02/16 21:24:27 mdw |
| 33 | * Rewrite for new key exchange protocol. |
| 34 | * |
| 35 | * Revision 1.1 2001/02/03 20:26:37 mdw |
| 36 | * Initial checkin. |
| 37 | * |
| 38 | */ |
| 39 | |
| 40 | /*----- Header files ------------------------------------------------------*/ |
| 41 | |
| 42 | #include "tripe.h" |
| 43 | |
| 44 | /*----- Tunable parameters ------------------------------------------------*/ |
| 45 | |
| 46 | #define T_VALID MIN(2) |
| 47 | #define T_RETRY SEC(10) |
| 48 | |
| 49 | #define ISVALID(kx, now) ((now) < (kx)->t_valid) |
| 50 | |
| 51 | /*----- Various utilities -------------------------------------------------*/ |
| 52 | |
| 53 | /* --- @hashmp@ --- * |
| 54 | * |
| 55 | * Arguments: @HASH_CTX *r@ = pointer to hash context |
| 56 | * @mp *m@ = pointer to multiprecision integer |
| 57 | * |
| 58 | * Returns: --- |
| 59 | * |
| 60 | * Use: Adds the hash of a multiprecision integer to the context. |
| 61 | * Corrupts @buf_t@. |
| 62 | */ |
| 63 | |
| 64 | static void hashmp(HASH_CTX *r, mp *m) |
| 65 | { |
| 66 | buf b; |
| 67 | buf_init(&b, buf_t, sizeof(buf_t)); |
| 68 | buf_putmp(&b, m); |
| 69 | assert(BOK(&b)); |
| 70 | HASH(r, BBASE(&b), BLEN(&b)); |
| 71 | } |
| 72 | |
| 73 | /* --- @timer@ --- * |
| 74 | * |
| 75 | * Arguments: @struct timeval *tv@ = the current time |
| 76 | * @void *v@ = pointer to key exchange context |
| 77 | * |
| 78 | * Returns: --- |
| 79 | * |
| 80 | * Use: Acts when the key exchange timer goes off. |
| 81 | */ |
| 82 | |
| 83 | static void timer(struct timeval *tv, void *v) |
| 84 | { |
| 85 | keyexch *kx = v; |
| 86 | kx->f &= ~KXF_TIMER; |
| 87 | T( trace(T_KEYEXCH, "keyexch: timer has popped"); ) |
| 88 | kx_start(kx); |
| 89 | } |
| 90 | |
| 91 | /* --- @settimer@ --- * |
| 92 | * |
| 93 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 94 | * @time_t t@ = when to set the timer for |
| 95 | * |
| 96 | * Returns: --- |
| 97 | * |
| 98 | * Use: Sets the timer for the next key exchange attempt. |
| 99 | */ |
| 100 | |
| 101 | static void settimer(keyexch *kx, time_t t) |
| 102 | { |
| 103 | struct timeval tv; |
| 104 | if (kx->f & KXF_TIMER) |
| 105 | sel_rmtimer(&kx->t); |
| 106 | tv.tv_sec = t; |
| 107 | tv.tv_usec = 0; |
| 108 | sel_addtimer(&sel, &kx->t, &tv, timer, kx); |
| 109 | kx->f |= KXF_TIMER; |
| 110 | } |
| 111 | |
| 112 | /*----- Challenge management ----------------------------------------------*/ |
| 113 | |
| 114 | /* --- Notes on challenge management --- * |
| 115 | * |
| 116 | * We may get multiple different replies to our key exchange; some will be |
| 117 | * correct, some inserted by attackers. Up until @KX_THRESH@, all challenges |
| 118 | * received will be added to the table and given a full response. After |
| 119 | * @KX_THRESH@ distinct challenges are received, we return only a `cookie': |
| 120 | * our existing challenge, followed by a hash of the sender's challenge. We |
| 121 | * do %%\emph{not}%% give a bare challenge a reply slot at this stage. All |
| 122 | * properly-formed cookies are assigned a table slot: if none is spare, a |
| 123 | * used slot is randomly selected and destroyed. A cookie always receives a |
| 124 | * full reply. |
| 125 | */ |
| 126 | |
| 127 | /* --- @kxc_destroy@ --- * |
| 128 | * |
| 129 | * Arguments: @kxchal *kxc@ = pointer to the challenge block |
| 130 | * |
| 131 | * Returns: --- |
| 132 | * |
| 133 | * Use: Disposes of a challenge block. |
| 134 | */ |
| 135 | |
| 136 | static void kxc_destroy(kxchal *kxc) |
| 137 | { |
| 138 | if (kxc->f & KXF_TIMER) |
| 139 | sel_rmtimer(&kxc->t); |
| 140 | mp_drop(kxc->c); |
| 141 | mp_drop(kxc->r); |
| 142 | ks_drop(kxc->ks); |
| 143 | DESTROY(kxc); |
| 144 | } |
| 145 | |
| 146 | /* --- @kxc_stoptimer@ --- * |
| 147 | * |
| 148 | * Arguments: @kxchal *kxc@ = pointer to the challenge block |
| 149 | * |
| 150 | * Returns: --- |
| 151 | * |
| 152 | * Use: Stops the challenge's retry timer from sending messages. |
| 153 | * Useful when the state machine is in the endgame of the |
| 154 | * exchange. |
| 155 | */ |
| 156 | |
| 157 | static void kxc_stoptimer(kxchal *kxc) |
| 158 | { |
| 159 | if (kxc->f & KXF_TIMER) |
| 160 | sel_rmtimer(&kxc->t); |
| 161 | } |
| 162 | |
| 163 | /* --- @kxc_new@ --- * |
| 164 | * |
| 165 | * Arguments: @keyexch *kx@ = pointer to key exchange block |
| 166 | * @ |
| 167 | * |
| 168 | * Returns: A pointer to the challenge block. |
| 169 | * |
| 170 | * Use: Returns a pointer to a new challenge block to fill in. |
| 171 | */ |
| 172 | |
| 173 | static kxchal *kxc_new(keyexch *kx) |
| 174 | { |
| 175 | kxchal *kxc; |
| 176 | unsigned i; |
| 177 | |
| 178 | /* --- If we're over reply threshold, discard one at random --- */ |
| 179 | |
| 180 | if (kx->nr < KX_NCHAL) |
| 181 | i = kx->nr++; |
| 182 | else { |
| 183 | i = rand_global.ops->range(&rand_global, KX_NCHAL); |
| 184 | kxc_destroy(kx->r[i]); |
| 185 | } |
| 186 | |
| 187 | /* --- Fill in the new structure --- */ |
| 188 | |
| 189 | kxc = CREATE(kxchal); |
| 190 | kxc->c = 0; |
| 191 | kxc->r = 0; |
| 192 | kxc->ks = 0; |
| 193 | kxc->kx = kx; |
| 194 | kxc->f = 0; |
| 195 | kx->r[i] = kxc; |
| 196 | return (kxc); |
| 197 | } |
| 198 | |
| 199 | /* --- @kxc_bychal@ --- * |
| 200 | * |
| 201 | * Arguments: @keyexch *kx@ = pointer to key exchange block |
| 202 | * @mp *c@ = challenge from remote host |
| 203 | * |
| 204 | * Returns: Pointer to the challenge block, or null. |
| 205 | * |
| 206 | * Use: Finds a challenge block, given its challenge. |
| 207 | */ |
| 208 | |
| 209 | static kxchal *kxc_bychal(keyexch *kx, mp *c) |
| 210 | { |
| 211 | unsigned i; |
| 212 | |
| 213 | for (i = 0; i < kx->nr; i++) { |
| 214 | if (MP_EQ(c, kx->r[i]->c)) |
| 215 | return (kx->r[i]); |
| 216 | } |
| 217 | return (0); |
| 218 | } |
| 219 | |
| 220 | /* --- @kxc_byhc@ --- * |
| 221 | * |
| 222 | * Arguments: @keyexch *kx@ = pointer to key exchange block |
| 223 | * @const octet *hc@ = challenge hash from remote host |
| 224 | * |
| 225 | * Returns: Pointer to the challenge block, or null. |
| 226 | * |
| 227 | * Use: Finds a challenge block, given a hash of its challenge. |
| 228 | */ |
| 229 | |
| 230 | static kxchal *kxc_byhc(keyexch *kx, const octet *hc) |
| 231 | { |
| 232 | unsigned i; |
| 233 | |
| 234 | for (i = 0; i < kx->nr; i++) { |
| 235 | if (memcmp(hc, kx->r[i]->hc, HASHSZ) == 0) |
| 236 | return (kx->r[i]); |
| 237 | } |
| 238 | return (0); |
| 239 | } |
| 240 | |
| 241 | /* --- @kxc_answer@ --- * |
| 242 | * |
| 243 | * Arguments: @keyexch *kx@ = pointer to key exchange block |
| 244 | * @kxchal *kxc@ = pointer to challenge block |
| 245 | * |
| 246 | * Returns: --- |
| 247 | * |
| 248 | * Use: Sends a reply to the remote host, according to the data in |
| 249 | * this challenge block. |
| 250 | */ |
| 251 | |
| 252 | static void kxc_answer(keyexch *kx, kxchal *kxc); |
| 253 | |
| 254 | static void kxc_timer(struct timeval *tv, void *v) |
| 255 | { |
| 256 | kxchal *kxc = v; |
| 257 | kxc->f &= ~KXF_TIMER; |
| 258 | kxc_answer(kxc->kx, kxc); |
| 259 | } |
| 260 | |
| 261 | static void kxc_answer(keyexch *kx, kxchal *kxc) |
| 262 | { |
| 263 | stats *st = p_stats(kx->p); |
| 264 | buf *b = p_txstart(kx->p, MSG_KEYEXCH | (kxc->r ? KX_REPLY : KX_CHAL)); |
| 265 | struct timeval tv; |
| 266 | buf bb; |
| 267 | |
| 268 | /* --- Build the reply packet --- */ |
| 269 | |
| 270 | if (!kxc->r) |
| 271 | buf_putmp(b, kx->c); |
| 272 | else |
| 273 | buf_put(b, kx->hc, HASHSZ); |
| 274 | buf_put(b, kxc->hc, HASHSZ); |
| 275 | buf_put(b, kxc->hrx, HASHSZ); |
| 276 | |
| 277 | /* --- Maybe send an actual reply, if we have one --- */ |
| 278 | |
| 279 | if (!kxc->r) { |
| 280 | T( trace(T_KEYEXCH, "keyexch: resending challenge to `%s'", |
| 281 | p_name(kx->p)); ) |
| 282 | } else { |
| 283 | T( trace(T_KEYEXCH, "keyexch: sending reply to `%s'", p_name(kx->p)); ) |
| 284 | buf_init(&bb, buf_i, sizeof(buf_i)); |
| 285 | buf_putmp(&bb, kxc->r); |
| 286 | buf_flip(&bb); |
| 287 | ks_encrypt(kxc->ks, &bb, b); |
| 288 | } |
| 289 | |
| 290 | /* --- Update the statistics --- */ |
| 291 | |
| 292 | if (BOK(b)) { |
| 293 | st->n_kxout++; |
| 294 | st->sz_kxout += BLEN(b); |
| 295 | p_txend(kx->p); |
| 296 | } |
| 297 | |
| 298 | /* --- Schedule another resend --- */ |
| 299 | |
| 300 | if (kxc->f & KXF_TIMER) |
| 301 | sel_rmtimer(&kxc->t); |
| 302 | gettimeofday(&tv, 0); |
| 303 | tv.tv_sec += T_RETRY; |
| 304 | sel_addtimer(&sel, &kxc->t, &tv, kxc_timer, kxc); |
| 305 | kxc->f |= KXF_TIMER; |
| 306 | } |
| 307 | |
| 308 | /*----- Individual message handlers ---------------------------------------*/ |
| 309 | |
| 310 | /* --- @getreply@ --- * |
| 311 | * |
| 312 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 313 | * @mp *c@ = a challenge |
| 314 | * @const octet *hrx@ = the supplied expected-reply hash |
| 315 | * |
| 316 | * Returns: A pointer to the reply, or null if the reply-hash was wrong. |
| 317 | * |
| 318 | * Use: Computes replies to challenges. |
| 319 | */ |
| 320 | |
| 321 | static mp *getreply(keyexch *kx, mp *c, const octet *hrx) |
| 322 | { |
| 323 | mp *r = mpmont_exp(&mg, MP_NEW, c, kpriv.x); |
| 324 | HASH_CTX h; |
| 325 | octet buf[HASHSZ]; |
| 326 | |
| 327 | HASH_INIT(&h); |
| 328 | HASH_STRING(&h, "tripe-expected-reply"); |
| 329 | hashmp(&h, c); |
| 330 | hashmp(&h, kx->c); |
| 331 | hashmp(&h, r); |
| 332 | HASH_DONE(&h, buf); |
| 333 | IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, { |
| 334 | trace(T_CRYPTO, "crypto: computed reply = %s", mpstr(r)); |
| 335 | trace_block(T_CRYPTO, "crypto: computed reply hash", buf, HASHSZ); |
| 336 | })) |
| 337 | if (memcmp(buf, hrx, HASHSZ) != 0) { |
| 338 | a_warn("invalid expected-reply hash from `%s'", p_name(kx->p)); |
| 339 | mp_drop(r); |
| 340 | return (0); |
| 341 | } |
| 342 | return (r); |
| 343 | } |
| 344 | |
| 345 | /* --- @dochallenge@ --- * |
| 346 | * |
| 347 | * Arguments: @keyexch *kx@ = pointer to key exchange block |
| 348 | * @unsigned msg@ = message code for the packet |
| 349 | * @buf *b@ = buffer containing the packet |
| 350 | * |
| 351 | * Returns: Zero if OK, nonzero if the packet was rejected. |
| 352 | * |
| 353 | * Use: Processes a packet containing a challenge. |
| 354 | */ |
| 355 | |
| 356 | static int dochallenge(keyexch *kx, unsigned msg, buf *b) |
| 357 | { |
| 358 | mp *c = 0; |
| 359 | const octet *hc = 0, *hrx = 0; |
| 360 | kxchal *kxc; |
| 361 | HASH_CTX h; |
| 362 | |
| 363 | /* --- Ensure that we're in a sensible state --- */ |
| 364 | |
| 365 | if (kx->s != KXS_CHAL) { |
| 366 | a_warn("unexpected challenge from `%s'", p_name(kx->p)); |
| 367 | goto bad; |
| 368 | } |
| 369 | |
| 370 | /* --- Unpack the packet --- */ |
| 371 | |
| 372 | if ((c = buf_getmp(b)) == 0 || |
| 373 | (msg >= KX_COOKIE && (hc = buf_get(b, HASHSZ)) == 0) || |
| 374 | (msg >= KX_CHAL && (hrx = buf_get(b, HASHSZ)) == 0) || |
| 375 | BLEFT(b)) { |
| 376 | a_warn("malformed packet from `%s'", p_name(kx->p)); |
| 377 | goto bad; |
| 378 | } |
| 379 | |
| 380 | IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, { |
| 381 | trace(T_CRYPTO, "crypto: challenge = %s", mpstr(c)); |
| 382 | if (hc) trace_block(T_CRYPTO, "crypto: cookie", hc, HASHSZ); |
| 383 | if (hrx) trace_block(T_CRYPTO, "crypto: response hash", hrx, HASHSZ); |
| 384 | })) |
| 385 | |
| 386 | /* --- First, handle a bare challenge --- * |
| 387 | * |
| 388 | * If the table is heavily loaded, just emit a cookie and return. |
| 389 | */ |
| 390 | |
| 391 | if (!hc && kx->nr >= KX_THRESH) { |
| 392 | T( trace(T_KEYEXCH, "keyexch: too many challenges -- sending cookie"); ) |
| 393 | b = p_txstart(kx->p, MSG_KEYEXCH | KX_COOKIE); |
| 394 | buf_putmp(b, kx->c); |
| 395 | HASH_INIT(&h); |
| 396 | HASH_STRING(&h, "tripe-cookie"); |
| 397 | hashmp(&h, c); |
| 398 | HASH_DONE(&h, buf_get(b, HASHSZ)); |
| 399 | p_txend(kx->p); |
| 400 | goto tidy; |
| 401 | } |
| 402 | |
| 403 | /* --- Discard a packet with an invalid cookie --- */ |
| 404 | |
| 405 | if (hc && memcmp(hc, kx->hc, HASHSZ) != 0) { |
| 406 | a_warn("incorrect cookie from `%s'", p_name(kx->p)); |
| 407 | goto bad; |
| 408 | } |
| 409 | |
| 410 | /* --- Find a challenge block for this packet --- * |
| 411 | * |
| 412 | * If there isn't one already, create a new one. |
| 413 | */ |
| 414 | |
| 415 | if ((kxc = kxc_bychal(kx, c)) == 0) { |
| 416 | size_t x, y, z; |
| 417 | mp *r; |
| 418 | |
| 419 | /* --- Be careful here --- * |
| 420 | * |
| 421 | * If this is a full challenge, and it's the first time I've seen it, I |
| 422 | * want to be able to throw it away before committing a table entry to |
| 423 | * it. |
| 424 | */ |
| 425 | |
| 426 | if (!hrx) |
| 427 | kxc = kxc_new(kx); |
| 428 | else { |
| 429 | if ((r = getreply(kx, c, hrx)) == 0) |
| 430 | goto bad; |
| 431 | kxc = kxc_new(kx); |
| 432 | kxc->r = r; |
| 433 | } |
| 434 | kxc->c = mp_copy(c); |
| 435 | |
| 436 | /* --- Work out the cookie for this challenge --- */ |
| 437 | |
| 438 | HASH_INIT(&h); |
| 439 | HASH_STRING(&h, "tripe-cookie"); |
| 440 | hashmp(&h, kxc->c); |
| 441 | HASH_DONE(&h, kxc->hc); |
| 442 | |
| 443 | /* --- Compute the expected-reply hash --- */ |
| 444 | |
| 445 | HASH_INIT(&h); |
| 446 | HASH_STRING(&h, "tripe-expected-reply"); |
| 447 | hashmp(&h, kx->c); |
| 448 | hashmp(&h, kxc->c); |
| 449 | hashmp(&h, kx->rx); |
| 450 | HASH_DONE(&h, kxc->hrx); |
| 451 | |
| 452 | /* --- Work out the shared key --- */ |
| 453 | |
| 454 | r = mpmont_exp(&mg, MP_NEW, c, kx->alpha); |
| 455 | |
| 456 | /* --- Compute the switch messages --- */ |
| 457 | |
| 458 | HASH_INIT(&h); HASH_STRING(&h, "tripe-switch-request"); |
| 459 | hashmp(&h, kx->c); hashmp(&h, kxc->c); |
| 460 | HASH_DONE(&h, kxc->hswrq_out); |
| 461 | HASH_INIT(&h); HASH_STRING(&h, "tripe-switch-confirm"); |
| 462 | hashmp(&h, kx->c); hashmp(&h, kxc->c); |
| 463 | HASH_DONE(&h, kxc->hswok_out); |
| 464 | |
| 465 | HASH_INIT(&h); HASH_STRING(&h, "tripe-switch-request"); |
| 466 | hashmp(&h, kxc->c); hashmp(&h, kx->c); |
| 467 | HASH_DONE(&h, kxc->hswrq_in); |
| 468 | HASH_INIT(&h); HASH_STRING(&h, "tripe-switch-confirm"); |
| 469 | hashmp(&h, kxc->c); hashmp(&h, kx->c); |
| 470 | HASH_DONE(&h, kxc->hswok_in); |
| 471 | |
| 472 | IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, { |
| 473 | trace_block(T_CRYPTO, "crypto: computed cookie", kxc->hc, HASHSZ); |
| 474 | trace_block(T_CRYPTO, "crypto: my reply hash", kxc->hrx, HASHSZ); |
| 475 | trace(T_CRYPTO, "crypto: shared secret = %s", mpstr(r)); |
| 476 | trace_block(T_CRYPTO, "crypto: outbound switch request", |
| 477 | kxc->hswrq_out, HASHSZ); |
| 478 | trace_block(T_CRYPTO, "crypto: outbound switch confirm", |
| 479 | kxc->hswok_out, HASHSZ); |
| 480 | trace_block(T_CRYPTO, "crypto: inbound switch request", |
| 481 | kxc->hswrq_in, HASHSZ); |
| 482 | trace_block(T_CRYPTO, "crypto: inbound switch confirm", |
| 483 | kxc->hswok_in, HASHSZ); |
| 484 | })) |
| 485 | |
| 486 | /* --- Create a new symmetric keyset --- */ |
| 487 | |
| 488 | buf_init(b, buf_o, sizeof(buf_o)); |
| 489 | buf_putmp(b, kx->c); x = BLEN(b); |
| 490 | buf_putmp(b, kxc->c); y = BLEN(b); |
| 491 | buf_putmp(b, r); z = BLEN(b); |
| 492 | assert(BOK(b)); |
| 493 | |
| 494 | kxc->ks = ks_gen(BBASE(b), x, y, z); |
| 495 | mp_drop(r); |
| 496 | } |
| 497 | |
| 498 | /* --- Answer the challenge if we need to --- */ |
| 499 | |
| 500 | if (hrx && !kxc->r) { |
| 501 | mp *r; |
| 502 | if ((r = getreply(kx, c, hrx)) == 0) |
| 503 | goto bad; |
| 504 | kxc->r = r; |
| 505 | } |
| 506 | |
| 507 | kxc_answer(kx, kxc); |
| 508 | |
| 509 | /* --- Tidy up and go home --- */ |
| 510 | |
| 511 | tidy: |
| 512 | mp_drop(c); |
| 513 | return (0); |
| 514 | |
| 515 | bad: |
| 516 | mp_drop(c); |
| 517 | return (-1); |
| 518 | } |
| 519 | |
| 520 | /* --- @resend@ --- * |
| 521 | * |
| 522 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 523 | * |
| 524 | * Returns: --- |
| 525 | * |
| 526 | * Use: Sends the next message for a key exchange. |
| 527 | */ |
| 528 | |
| 529 | static void resend(keyexch *kx) |
| 530 | { |
| 531 | kxchal *kxc; |
| 532 | buf bb; |
| 533 | stats *st = p_stats(kx->p); |
| 534 | buf *b; |
| 535 | |
| 536 | switch (kx->s) { |
| 537 | case KXS_CHAL: |
| 538 | T( trace(T_KEYEXCH, "sending prechallenge to `%s'", p_name(kx->p)); ) |
| 539 | b = p_txstart(kx->p, MSG_KEYEXCH | KX_PRECHAL); |
| 540 | buf_putmp(b, kx->c); |
| 541 | break; |
| 542 | case KXS_COMMIT: |
| 543 | T( trace(T_KEYEXCH, "sending switch request to `%s'", p_name(kx->p)); ) |
| 544 | kxc = kx->r[0]; |
| 545 | b = p_txstart(kx->p, MSG_KEYEXCH | KX_SWITCH); |
| 546 | buf_put(b, kx->hc, HASHSZ); |
| 547 | buf_put(b, kxc->hc, HASHSZ); |
| 548 | buf_init(&bb, buf_i, sizeof(buf_i)); |
| 549 | buf_putmp(&bb, kxc->r); |
| 550 | buf_put(&bb, kxc->hswrq_out, HASHSZ); |
| 551 | buf_flip(&bb); |
| 552 | ks_encrypt(kxc->ks, &bb, b); |
| 553 | break; |
| 554 | case KXS_SWITCH: |
| 555 | T( trace(T_KEYEXCH, "sending switch confirmation to `%s'", |
| 556 | p_name(kx->p)); ) |
| 557 | kxc = kx->r[0]; |
| 558 | b = p_txstart(kx->p, MSG_KEYEXCH | KX_SWITCHOK); |
| 559 | buf_init(&bb, buf_i, sizeof(buf_i)); |
| 560 | buf_put(&bb, kxc->hswok_out, HASHSZ); |
| 561 | buf_flip(&bb); |
| 562 | ks_encrypt(kxc->ks, &bb, b); |
| 563 | break; |
| 564 | default: |
| 565 | abort(); |
| 566 | } |
| 567 | |
| 568 | if (BOK(b)) { |
| 569 | st->n_kxout++; |
| 570 | st->sz_kxout += BLEN(b); |
| 571 | p_txend(kx->p); |
| 572 | } |
| 573 | |
| 574 | if (kx->s < KXS_SWITCH) |
| 575 | settimer(kx, time(0) + T_RETRY); |
| 576 | } |
| 577 | |
| 578 | /* --- @matchreply@ --- * |
| 579 | * |
| 580 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 581 | * @const octet *hc_in@ = a hash of his challenge |
| 582 | * @const octet *hc_out@ = a hash of my challenge (cookie) |
| 583 | * @const octet *krx@ = his expected-reply hash (optional) |
| 584 | * @buf *b@ = encrypted remainder of the packet |
| 585 | * |
| 586 | * Returns: A pointer to the challenge block if OK, or null on failure. |
| 587 | * |
| 588 | * Use: Checks a reply or switch packet, ensuring that its contents |
| 589 | * are sensible and correct. If they are, @*b@ is set to point |
| 590 | * to the remainder of the encrypted data, and the correct |
| 591 | * challenge is returned. |
| 592 | */ |
| 593 | |
| 594 | static kxchal *matchreply(keyexch *kx, const octet *hc_in, |
| 595 | const octet *hc_out, const octet *hrx, buf *b) |
| 596 | { |
| 597 | kxchal *kxc; |
| 598 | buf bb; |
| 599 | mp *r = 0; |
| 600 | |
| 601 | /* --- Check the plaintext portions of the data --- */ |
| 602 | |
| 603 | IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, { |
| 604 | trace_block(T_CRYPTO, "crypto: challenge", hc_in, HASHSZ); |
| 605 | trace_block(T_CRYPTO, "crypto: cookie", hc_out, HASHSZ); |
| 606 | if (hrx) trace_block(T_CRYPTO, "crypto: response hash", hrx, HASHSZ); |
| 607 | })) |
| 608 | if (memcmp(hc_out, kx->hc, HASHSZ) != 0) { |
| 609 | a_warn("incorrect cookie from `%s'", p_name(kx->p)); |
| 610 | goto bad; |
| 611 | } |
| 612 | if ((kxc = kxc_byhc(kx, hc_in)) == 0) { |
| 613 | a_warn("received reply for unknown challenge from `%s'", p_name(kx->p)); |
| 614 | goto bad; |
| 615 | } |
| 616 | |
| 617 | /* --- Maybe compute a reply for the challenge --- */ |
| 618 | |
| 619 | if (!kxc->r) { |
| 620 | if (!hrx) { |
| 621 | a_warn("unexpected switch request from `%s'", p_name(kx->p)); |
| 622 | goto bad; |
| 623 | } |
| 624 | if ((r = getreply(kx, kxc->c, hrx)) == 0) |
| 625 | goto bad; |
| 626 | kxc->r = r; |
| 627 | r = 0; |
| 628 | } |
| 629 | |
| 630 | /* --- Decrypt the rest of the packet --- */ |
| 631 | |
| 632 | buf_init(&bb, buf_o, sizeof(buf_o)); |
| 633 | if (ks_decrypt(kxc->ks, b, &bb)) { |
| 634 | a_warn("failed to decrypt reply from `%s'", p_name(kx->p)); |
| 635 | goto bad; |
| 636 | } |
| 637 | buf_init(b, BBASE(&bb), BLEN(&bb)); |
| 638 | if ((r = buf_getmp(b)) == 0) { |
| 639 | a_warn("invalid reply packet from `%s'", p_name(kx->p)); |
| 640 | goto bad; |
| 641 | } |
| 642 | IF_TRACING(T_KEYEXCH, IF_TRACING(T_CRYPTO, { |
| 643 | trace(T_CRYPTO, "crypto: reply = %s", mpstr(r)); |
| 644 | })) |
| 645 | if (!mp_eq(r, kx->rx)) { |
| 646 | a_warn("incorrect reply from `%s'", p_name(kx->p)); |
| 647 | goto bad; |
| 648 | } |
| 649 | |
| 650 | /* --- Done --- */ |
| 651 | |
| 652 | mp_drop(r); |
| 653 | return (kxc); |
| 654 | |
| 655 | bad: |
| 656 | mp_drop(r); |
| 657 | return (0); |
| 658 | } |
| 659 | |
| 660 | /* --- @commit@ --- * |
| 661 | * |
| 662 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 663 | * @kxchal *kxc@ = pointer to challenge to commit to |
| 664 | * |
| 665 | * Returns: --- |
| 666 | * |
| 667 | * Use: Commits to a particular challenge as being the `right' one, |
| 668 | * since a reply has arrived for it. |
| 669 | */ |
| 670 | |
| 671 | static void commit(keyexch *kx, kxchal *kxc) |
| 672 | { |
| 673 | unsigned i; |
| 674 | |
| 675 | for (i = 0; i < kx->nr; i++) { |
| 676 | if (kx->r[i] != kxc) |
| 677 | kxc_destroy(kx->r[i]); |
| 678 | } |
| 679 | kx->r[0] = kxc; |
| 680 | kx->nr = 1; |
| 681 | kxc_stoptimer(kxc); |
| 682 | ksl_link(kx->ks, kxc->ks); |
| 683 | } |
| 684 | |
| 685 | /* --- @doreply@ --- * |
| 686 | * |
| 687 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 688 | * @buf *b@ = buffer containing packet |
| 689 | * |
| 690 | * Returns: Zero if OK, nonzero if the packet was rejected. |
| 691 | * |
| 692 | * Use: Handles a reply packet. This doesn't handle the various |
| 693 | * switch packets: they're rather too different. |
| 694 | */ |
| 695 | |
| 696 | static int doreply(keyexch *kx, buf *b) |
| 697 | { |
| 698 | const octet *hc_in, *hc_out, *hrx; |
| 699 | kxchal *kxc; |
| 700 | |
| 701 | if (kx->s != KXS_CHAL && kx->s != KXS_COMMIT) { |
| 702 | a_warn("unexpected reply from `%s'", p_name(kx->p)); |
| 703 | goto bad; |
| 704 | } |
| 705 | if ((hc_in = buf_get(b, HASHSZ)) == 0 || |
| 706 | (hc_out = buf_get(b, HASHSZ)) == 0 || |
| 707 | (hrx = buf_get(b, HASHSZ)) == 0) { |
| 708 | a_warn("invalid reply packet from `%s'", p_name(kx->p)); |
| 709 | goto bad; |
| 710 | } |
| 711 | if ((kxc = matchreply(kx, hc_in, hc_out, hrx, b)) == 0) |
| 712 | goto bad; |
| 713 | if (BLEFT(b)) { |
| 714 | a_warn("invalid reply packet from `%s'", p_name(kx->p)); |
| 715 | goto bad; |
| 716 | } |
| 717 | if (kx->s == KXS_CHAL) { |
| 718 | commit(kx, kxc); |
| 719 | kx->s = KXS_COMMIT; |
| 720 | } |
| 721 | resend(kx); |
| 722 | return (0); |
| 723 | |
| 724 | bad: |
| 725 | return (-1); |
| 726 | } |
| 727 | |
| 728 | /* --- @doswitch@ --- * |
| 729 | * |
| 730 | * Arguments: @keyexch *kx@ = pointer to key exchange block |
| 731 | * @buf *b@ = pointer to buffer containing packet |
| 732 | * |
| 733 | * Returns: Zero if OK, nonzero if the packet was rejected. |
| 734 | * |
| 735 | * Use: Handles a reply with a switch request bolted onto it. |
| 736 | */ |
| 737 | |
| 738 | static int doswitch(keyexch *kx, buf *b) |
| 739 | { |
| 740 | const octet *hc_in, *hc_out, *hswrq; |
| 741 | kxchal *kxc; |
| 742 | |
| 743 | if ((hc_in = buf_get(b, HASHSZ)) == 0 || |
| 744 | (hc_out = buf_get(b, HASHSZ)) == 0) { |
| 745 | a_warn("invalid switch request from `%s'", p_name(kx->p)); |
| 746 | goto bad; |
| 747 | } |
| 748 | if ((kxc = matchreply(kx, hc_in, hc_out, 0, b)) == 0) |
| 749 | goto bad; |
| 750 | if ((hswrq = buf_get(b, HASHSZ)) == 0 || BLEFT(b)) { |
| 751 | a_warn("invalid switch request from `%s'", p_name(kx->p)); |
| 752 | goto bad; |
| 753 | } |
| 754 | IF_TRACING(T_KEYEXCH, { |
| 755 | trace_block(T_CRYPTO, "crypto: switch request hash", hswrq, HASHSZ); |
| 756 | }) |
| 757 | if (memcmp(hswrq, kxc->hswrq_in, HASHSZ) != 0) { |
| 758 | a_warn("incorrect switch request hash from `%s'", p_name(kx->p)); |
| 759 | goto bad; |
| 760 | } |
| 761 | switch (kx->s) { |
| 762 | case KXS_CHAL: |
| 763 | commit(kx, kxc); |
| 764 | case KXS_COMMIT: |
| 765 | ks_activate(kxc->ks); |
| 766 | settimer(kx, ks_tregen(kxc->ks)); |
| 767 | kx->s = KXS_SWITCH; |
| 768 | break; |
| 769 | } |
| 770 | resend(kx); |
| 771 | return (0); |
| 772 | |
| 773 | bad: |
| 774 | return (-1); |
| 775 | } |
| 776 | |
| 777 | /* --- @doswitchok@ --- * |
| 778 | * |
| 779 | * Arguments: @keyexch *kx@ = pointer to key exchange block |
| 780 | * @buf *b@ = pointer to buffer containing packet |
| 781 | * |
| 782 | * Returns: Zero if OK, nonzero if the packet was rejected. |
| 783 | * |
| 784 | * Use: Handles a reply with a switch request bolted onto it. |
| 785 | */ |
| 786 | |
| 787 | static int doswitchok(keyexch *kx, buf *b) |
| 788 | { |
| 789 | const octet *hswok; |
| 790 | kxchal *kxc; |
| 791 | buf bb; |
| 792 | |
| 793 | if (kx->s < KXS_COMMIT) { |
| 794 | a_warn("unexpected switch confirmation from `%s'", p_name(kx->p)); |
| 795 | goto bad; |
| 796 | } |
| 797 | kxc = kx->r[0]; |
| 798 | buf_init(&bb, buf_o, sizeof(buf_o)); |
| 799 | if (ks_decrypt(kxc->ks, b, &bb)) { |
| 800 | a_warn("failed to decrypt switch confirmation from `%s'", p_name(kx->p)); |
| 801 | goto bad; |
| 802 | } |
| 803 | buf_init(b, BBASE(&bb), BLEN(&bb)); |
| 804 | if ((hswok = buf_get(b, HASHSZ)) == 0 || BLEFT(b)) { |
| 805 | a_warn("invalid switch confirmation from `%s'", p_name(kx->p)); |
| 806 | goto bad; |
| 807 | } |
| 808 | IF_TRACING(T_KEYEXCH, { |
| 809 | trace_block(T_CRYPTO, "crypto: switch confirmation hash", hswok, HASHSZ); |
| 810 | }) |
| 811 | if (memcmp(hswok, kxc->hswok_in, HASHSZ) != 0) { |
| 812 | a_warn("incorrect switch confirmation hash from `%s'", p_name(kx->p)); |
| 813 | goto bad; |
| 814 | } |
| 815 | if (kx->s < KXS_SWITCH) { |
| 816 | ks_activate(kxc->ks); |
| 817 | settimer(kx, ks_tregen(kxc->ks)); |
| 818 | kx->s = KXS_SWITCH; |
| 819 | } |
| 820 | return (0); |
| 821 | |
| 822 | bad: |
| 823 | return (-1); |
| 824 | } |
| 825 | |
| 826 | /*----- Main code ---------------------------------------------------------*/ |
| 827 | |
| 828 | /* --- @stop@ --- * |
| 829 | * |
| 830 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 831 | * |
| 832 | * Returns: --- |
| 833 | * |
| 834 | * Use: Stops a key exchange dead in its tracks. Throws away all of |
| 835 | * the context information. The context is left in an |
| 836 | * inconsistent state. The only functions which understand this |
| 837 | * state are @kx_free@ and @kx_init@ (which cause it internally |
| 838 | * it), and @start@ (which expects it to be the prevailing |
| 839 | * state). |
| 840 | */ |
| 841 | |
| 842 | static void stop(keyexch *kx) |
| 843 | { |
| 844 | unsigned i; |
| 845 | |
| 846 | if (kx->f & KXF_TIMER) |
| 847 | sel_rmtimer(&kx->t); |
| 848 | for (i = 0; i < kx->nr; i++) |
| 849 | kxc_destroy(kx->r[i]); |
| 850 | mp_drop(kx->alpha); |
| 851 | mp_drop(kx->c); |
| 852 | mp_drop(kx->rx); |
| 853 | } |
| 854 | |
| 855 | /* --- @start@ --- * |
| 856 | * |
| 857 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 858 | * @time_t now@ = the current time |
| 859 | * |
| 860 | * Returns: --- |
| 861 | * |
| 862 | * Use: Starts a new key exchange with the peer. The context must be |
| 863 | * in the bizarre state left by @stop@ or @kx_init@. |
| 864 | */ |
| 865 | |
| 866 | static void start(keyexch *kx, time_t now) |
| 867 | { |
| 868 | HASH_CTX h; |
| 869 | |
| 870 | kx->nr = 0; |
| 871 | kx->f = 0; |
| 872 | kx->alpha = mprand_range(MP_NEW, kpriv.dp.q, &rand_global, 0); |
| 873 | kx->c = mpmont_exp(&mg, MP_NEW, kpriv.dp.g, kx->alpha); |
| 874 | kx->rx = mpmont_exp(&mg, MP_NEW, kx->kpub.y, kx->alpha); |
| 875 | kx->s = KXS_CHAL; |
| 876 | kx->t_valid = now + T_VALID; |
| 877 | |
| 878 | HASH_INIT(&h); |
| 879 | HASH_STRING(&h, "tripe-cookie"); |
| 880 | hashmp(&h, kx->c); |
| 881 | HASH_DONE(&h, kx->hc); |
| 882 | |
| 883 | IF_TRACING(T_KEYEXCH, { |
| 884 | trace(T_KEYEXCH, "keyexch: creating new challenge"); |
| 885 | IF_TRACING(T_CRYPTO, { |
| 886 | trace(T_CRYPTO, "crypto: secret = %s", mpstr(kx->alpha)); |
| 887 | trace(T_CRYPTO, "crypto: challenge = %s", mpstr(kx->c)); |
| 888 | trace(T_CRYPTO, "crypto: expected response = %s", mpstr(kx->rx)); |
| 889 | trace_block(T_CRYPTO, "crypto: challenge cookie", kx->hc, HASHSZ); |
| 890 | }) |
| 891 | }) |
| 892 | } |
| 893 | |
| 894 | /* --- @kx_start@ --- * |
| 895 | * |
| 896 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 897 | * |
| 898 | * Returns: --- |
| 899 | * |
| 900 | * Use: Stimulates a key exchange. If a key exchage is in progress, |
| 901 | * a new challenge is sent (unless the quiet timer forbids |
| 902 | * this); if no exchange is in progress, one is commenced. |
| 903 | */ |
| 904 | |
| 905 | void kx_start(keyexch *kx) |
| 906 | { |
| 907 | time_t now = time(0); |
| 908 | |
| 909 | if (!ISVALID(kx, now)) { |
| 910 | stop(kx); |
| 911 | start(kx, now); |
| 912 | } |
| 913 | resend(kx); |
| 914 | } |
| 915 | |
| 916 | /* --- @kx_message@ --- * |
| 917 | * |
| 918 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 919 | * @unsigned msg@ = the message code |
| 920 | * @buf *b@ = pointer to buffer containing the packet |
| 921 | * |
| 922 | * Returns: --- |
| 923 | * |
| 924 | * Use: Reads a packet containing key exchange messages and handles |
| 925 | * it. |
| 926 | */ |
| 927 | |
| 928 | void kx_message(keyexch *kx, unsigned msg, buf *b) |
| 929 | { |
| 930 | time_t now = time(0); |
| 931 | stats *st = p_stats(kx->p); |
| 932 | size_t sz = BSZ(b); |
| 933 | int rc; |
| 934 | |
| 935 | #ifndef NTRACE |
| 936 | static const char *const pkname[] = { |
| 937 | "prechallenge", "cookie", "challenge", |
| 938 | "reply", "switch request", "switch confirmation" |
| 939 | }; |
| 940 | #endif |
| 941 | |
| 942 | if (!ISVALID(kx, now)) { |
| 943 | stop(kx); |
| 944 | start(kx, now); |
| 945 | } |
| 946 | |
| 947 | T( trace(T_KEYEXCH, "keyexch: processing %s packet from `%s'", |
| 948 | msg < KX_NMSG ? pkname[msg] : "unknown", p_name(kx->p)); ) |
| 949 | |
| 950 | switch (msg) { |
| 951 | case KX_PRECHAL: |
| 952 | case KX_COOKIE: |
| 953 | case KX_CHAL: |
| 954 | rc = dochallenge(kx, msg, b); |
| 955 | break; |
| 956 | case KX_REPLY: |
| 957 | rc = doreply(kx, b); |
| 958 | break; |
| 959 | case KX_SWITCH: |
| 960 | rc = doswitch(kx, b); |
| 961 | break; |
| 962 | case KX_SWITCHOK: |
| 963 | rc = doswitchok(kx, b); |
| 964 | break; |
| 965 | default: |
| 966 | a_warn("unexpected key exchange message type %u from `%p'", |
| 967 | p_name(kx->p)); |
| 968 | rc = -1; |
| 969 | break; |
| 970 | } |
| 971 | |
| 972 | if (rc) |
| 973 | st->n_reject++; |
| 974 | else { |
| 975 | st->n_kxin++; |
| 976 | st->sz_kxin += sz; |
| 977 | } |
| 978 | } |
| 979 | |
| 980 | /* --- @kx_free@ --- * |
| 981 | * |
| 982 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 983 | * |
| 984 | * Returns: --- |
| 985 | * |
| 986 | * Use: Frees everything in a key exchange context. |
| 987 | */ |
| 988 | |
| 989 | void kx_free(keyexch *kx) |
| 990 | { |
| 991 | stop(kx); |
| 992 | dh_pubfree(&kx->kpub); |
| 993 | } |
| 994 | |
| 995 | /* --- @kx_newkeys@ --- * |
| 996 | * |
| 997 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 998 | * |
| 999 | * Returns: --- |
| 1000 | * |
| 1001 | * Use: Informs the key exchange module that its keys may have |
| 1002 | * changed. If fetching the new keys fails, the peer will be |
| 1003 | * destroyed, we log messages and struggle along with the old |
| 1004 | * keys. |
| 1005 | */ |
| 1006 | |
| 1007 | void kx_newkeys(keyexch *kx) |
| 1008 | { |
| 1009 | dh_pub dp; |
| 1010 | |
| 1011 | if (km_getpubkey(p_name(kx->p), &dp)) |
| 1012 | return; |
| 1013 | dh_pubfree(&kx->kpub); |
| 1014 | kx->kpub = dp; |
| 1015 | if (kx->s != KXS_SWITCH) { |
| 1016 | T( trace(T_KEYEXCH, "keyexch: restarting key negotiation with `%s'", |
| 1017 | p_name(kx->p)); ) |
| 1018 | kx->t_valid = 0; |
| 1019 | kx_start(kx); |
| 1020 | } |
| 1021 | } |
| 1022 | |
| 1023 | /* --- @kx_init@ --- * |
| 1024 | * |
| 1025 | * Arguments: @keyexch *kx@ = pointer to key exchange context |
| 1026 | * @peer *p@ = pointer to peer context |
| 1027 | * @keyset **ks@ = pointer to keyset list |
| 1028 | * |
| 1029 | * Returns: Zero if OK, nonzero if it failed. |
| 1030 | * |
| 1031 | * Use: Initializes a key exchange module. The module currently |
| 1032 | * contains no keys, and will attempt to initiate a key |
| 1033 | * exchange. |
| 1034 | */ |
| 1035 | |
| 1036 | int kx_init(keyexch *kx, peer *p, keyset **ks) |
| 1037 | { |
| 1038 | kx->ks = ks; |
| 1039 | kx->p = p; |
| 1040 | if (km_getpubkey(p_name(p), &kx->kpub)) |
| 1041 | return (-1); |
| 1042 | start(kx, time(0)); |
| 1043 | resend(kx); |
| 1044 | return (0); |
| 1045 | } |
| 1046 | |
| 1047 | /*----- That's all, folks -------------------------------------------------*/ |