Annotation of src/usr.bin/ssh/kex.c, Revision 1.51.2.3
1.1 markus 1: /*
1.36 markus 2: * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
1.1 markus 3: *
4: * Redistribution and use in source and binary forms, with or without
5: * modification, are permitted provided that the following conditions
6: * are met:
7: * 1. Redistributions of source code must retain the above copyright
8: * notice, this list of conditions and the following disclaimer.
9: * 2. Redistributions in binary form must reproduce the above copyright
10: * notice, this list of conditions and the following disclaimer in the
11: * documentation and/or other materials provided with the distribution.
12: *
13: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23: */
24:
25: #include "includes.h"
1.51.2.2 margarid 26: RCSID("$OpenBSD: kex.c,v 1.55 2003/04/01 10:31:26 markus Exp $");
1.18 markus 27:
28: #include <openssl/crypto.h>
1.1 markus 29:
30: #include "ssh2.h"
31: #include "xmalloc.h"
32: #include "buffer.h"
33: #include "bufaux.h"
1.7 markus 34: #include "packet.h"
1.1 markus 35: #include "compat.h"
1.18 markus 36: #include "cipher.h"
1.1 markus 37: #include "kex.h"
1.13 markus 38: #include "key.h"
1.18 markus 39: #include "log.h"
1.21 markus 40: #include "mac.h"
1.23 markus 41: #include "match.h"
1.26 markus 42: #include "dispatch.h"
1.48 provos 43: #include "monitor.h"
1.1 markus 44:
1.7 markus 45: #define KEX_COOKIE_LEN 16
1.48 provos 46:
1.35 itojun 47: /* prototype */
48: static void kex_kexinit_finish(Kex *);
49: static void kex_choose_conf(Kex *);
1.26 markus 50:
51: /* put algorithm proposal into buffer */
1.35 itojun 52: static void
1.26 markus 53: kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
1.1 markus 54: {
55: int i;
1.26 markus 56:
57: buffer_clear(b);
1.49 markus 58: /*
59: * add a dummy cookie, the cookie will be overwritten by
60: * kex_send_kexinit(), each time a kexinit is set
61: */
62: for (i = 0; i < KEX_COOKIE_LEN; i++)
63: buffer_put_char(b, 0);
1.1 markus 64: for (i = 0; i < PROPOSAL_MAX; i++)
1.26 markus 65: buffer_put_cstring(b, proposal[i]);
66: buffer_put_char(b, 0); /* first_kex_packet_follows */
67: buffer_put_int(b, 0); /* uint32 reserved */
1.1 markus 68: }
69:
1.26 markus 70: /* parse buffer and return algorithm proposal */
1.35 itojun 71: static char **
1.51.2.1 margarid 72: kex_buf2prop(Buffer *raw, int *first_kex_follows)
1.7 markus 73: {
1.26 markus 74: Buffer b;
1.7 markus 75: int i;
1.26 markus 76: char **proposal;
1.7 markus 77:
1.26 markus 78: proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
1.7 markus 79:
1.26 markus 80: buffer_init(&b);
81: buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
1.7 markus 82: /* skip cookie */
83: for (i = 0; i < KEX_COOKIE_LEN; i++)
1.26 markus 84: buffer_get_char(&b);
1.7 markus 85: /* extract kex init proposal strings */
86: for (i = 0; i < PROPOSAL_MAX; i++) {
1.26 markus 87: proposal[i] = buffer_get_string(&b,NULL);
88: debug2("kex_parse_kexinit: %s", proposal[i]);
1.7 markus 89: }
1.26 markus 90: /* first kex follows / reserved */
91: i = buffer_get_char(&b);
1.51.2.1 margarid 92: if (first_kex_follows != NULL)
93: *first_kex_follows = i;
1.26 markus 94: debug2("kex_parse_kexinit: first_kex_follows %d ", i);
95: i = buffer_get_int(&b);
96: debug2("kex_parse_kexinit: reserved %d ", i);
97: buffer_free(&b);
98: return proposal;
1.1 markus 99: }
100:
1.35 itojun 101: static void
1.26 markus 102: kex_prop_free(char **proposal)
1.1 markus 103: {
104: int i;
1.26 markus 105:
106: for (i = 0; i < PROPOSAL_MAX; i++)
107: xfree(proposal[i]);
108: xfree(proposal);
1.1 markus 109: }
110:
1.35 itojun 111: static void
1.41 markus 112: kex_protocol_error(int type, u_int32_t seq, void *ctxt)
1.1 markus 113: {
1.41 markus 114: error("Hm, kex protocol error: type %d seq %u", type, seq);
1.26 markus 115: }
1.1 markus 116:
1.35 itojun 117: static void
1.44 markus 118: kex_reset_dispatch(void)
1.29 markus 119: {
1.42 markus 120: dispatch_range(SSH2_MSG_TRANSPORT_MIN,
121: SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
1.44 markus 122: dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
1.29 markus 123: }
124:
125: void
1.28 markus 126: kex_finish(Kex *kex)
1.26 markus 127: {
1.44 markus 128: kex_reset_dispatch();
1.28 markus 129:
1.26 markus 130: packet_start(SSH2_MSG_NEWKEYS);
131: packet_send();
132: /* packet_write_wait(); */
133: debug("SSH2_MSG_NEWKEYS sent");
1.19 stevesk 134:
1.51.2.1 margarid 135: debug("expecting SSH2_MSG_NEWKEYS");
1.40 markus 136: packet_read_expect(SSH2_MSG_NEWKEYS);
1.46 markus 137: packet_check_eom();
1.26 markus 138: debug("SSH2_MSG_NEWKEYS received");
1.32 markus 139:
1.30 markus 140: kex->done = 1;
1.26 markus 141: buffer_clear(&kex->peer);
1.27 markus 142: /* buffer_clear(&kex->my); */
1.26 markus 143: kex->flags &= ~KEX_INIT_SENT;
1.32 markus 144: xfree(kex->name);
145: kex->name = NULL;
1.26 markus 146: }
1.1 markus 147:
1.26 markus 148: void
149: kex_send_kexinit(Kex *kex)
150: {
1.49 markus 151: u_int32_t rand = 0;
152: u_char *cookie;
153: int i;
154:
1.29 markus 155: if (kex == NULL) {
156: error("kex_send_kexinit: no kex, cannot rekey");
157: return;
158: }
1.28 markus 159: if (kex->flags & KEX_INIT_SENT) {
160: debug("KEX_INIT_SENT");
161: return;
162: }
1.30 markus 163: kex->done = 0;
1.49 markus 164:
165: /* generate a random cookie */
166: if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
167: fatal("kex_send_kexinit: kex proposal too short");
168: cookie = buffer_ptr(&kex->my);
169: for (i = 0; i < KEX_COOKIE_LEN; i++) {
170: if (i % 4 == 0)
171: rand = arc4random();
172: cookie[i] = rand;
173: rand >>= 8;
174: }
1.26 markus 175: packet_start(SSH2_MSG_KEXINIT);
176: packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
177: packet_send();
178: debug("SSH2_MSG_KEXINIT sent");
179: kex->flags |= KEX_INIT_SENT;
1.1 markus 180: }
181:
1.26 markus 182: void
1.41 markus 183: kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
1.11 provos 184: {
1.26 markus 185: char *ptr;
186: int dlen;
1.31 markus 187: int i;
1.26 markus 188: Kex *kex = (Kex *)ctxt;
1.11 provos 189:
1.26 markus 190: debug("SSH2_MSG_KEXINIT received");
1.29 markus 191: if (kex == NULL)
192: fatal("kex_input_kexinit: no kex, cannot rekey");
1.11 provos 193:
1.26 markus 194: ptr = packet_get_raw(&dlen);
195: buffer_append(&kex->peer, ptr, dlen);
1.31 markus 196:
197: /* discard packet */
198: for (i = 0; i < KEX_COOKIE_LEN; i++)
199: packet_get_char();
200: for (i = 0; i < PROPOSAL_MAX; i++)
201: xfree(packet_get_string(NULL));
1.51 markus 202: (void) packet_get_char();
203: (void) packet_get_int();
1.39 markus 204: packet_check_eom();
1.19 stevesk 205:
1.26 markus 206: kex_kexinit_finish(kex);
207: }
1.11 provos 208:
1.26 markus 209: Kex *
1.28 markus 210: kex_setup(char *proposal[PROPOSAL_MAX])
1.26 markus 211: {
212: Kex *kex;
1.11 provos 213:
1.26 markus 214: kex = xmalloc(sizeof(*kex));
215: memset(kex, 0, sizeof(*kex));
216: buffer_init(&kex->peer);
217: buffer_init(&kex->my);
218: kex_prop2buf(&kex->my, proposal);
1.30 markus 219: kex->done = 0;
1.26 markus 220:
221: kex_send_kexinit(kex); /* we start */
1.44 markus 222: kex_reset_dispatch();
1.26 markus 223:
224: return kex;
1.11 provos 225: }
226:
1.35 itojun 227: static void
1.26 markus 228: kex_kexinit_finish(Kex *kex)
1.1 markus 229: {
1.26 markus 230: if (!(kex->flags & KEX_INIT_SENT))
231: kex_send_kexinit(kex);
1.1 markus 232:
1.26 markus 233: kex_choose_conf(kex);
1.1 markus 234:
1.51.2.1 margarid 235: if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
236: kex->kex[kex->kex_type] != NULL) {
237: (kex->kex[kex->kex_type])(kex);
238: } else {
1.26 markus 239: fatal("Unsupported key exchange %d", kex->kex_type);
1.1 markus 240: }
241: }
242:
1.35 itojun 243: static void
1.1 markus 244: choose_enc(Enc *enc, char *client, char *server)
245: {
1.23 markus 246: char *name = match_list(client, server, NULL);
1.1 markus 247: if (name == NULL)
248: fatal("no matching cipher found: client %s server %s", client, server);
1.45 markus 249: if ((enc->cipher = cipher_by_name(name)) == NULL)
1.12 markus 250: fatal("matching cipher is not supported: %s", name);
1.1 markus 251: enc->name = name;
252: enc->enabled = 0;
253: enc->iv = NULL;
254: enc->key = NULL;
1.45 markus 255: enc->key_len = cipher_keylen(enc->cipher);
256: enc->block_size = cipher_blocksize(enc->cipher);
1.1 markus 257: }
1.35 itojun 258: static void
1.1 markus 259: choose_mac(Mac *mac, char *client, char *server)
260: {
1.23 markus 261: char *name = match_list(client, server, NULL);
1.1 markus 262: if (name == NULL)
263: fatal("no matching mac found: client %s server %s", client, server);
1.21 markus 264: if (mac_init(mac, name) < 0)
1.1 markus 265: fatal("unsupported mac %s", name);
1.21 markus 266: /* truncate the key */
267: if (datafellows & SSH_BUG_HMAC)
268: mac->key_len = 16;
1.1 markus 269: mac->name = name;
270: mac->key = NULL;
271: mac->enabled = 0;
272: }
1.35 itojun 273: static void
1.1 markus 274: choose_comp(Comp *comp, char *client, char *server)
275: {
1.23 markus 276: char *name = match_list(client, server, NULL);
1.1 markus 277: if (name == NULL)
278: fatal("no matching comp found: client %s server %s", client, server);
279: if (strcmp(name, "zlib") == 0) {
280: comp->type = 1;
281: } else if (strcmp(name, "none") == 0) {
282: comp->type = 0;
283: } else {
284: fatal("unsupported comp %s", name);
285: }
286: comp->name = name;
287: }
1.35 itojun 288: static void
1.1 markus 289: choose_kex(Kex *k, char *client, char *server)
290: {
1.23 markus 291: k->name = match_list(client, server, NULL);
1.1 markus 292: if (k->name == NULL)
293: fatal("no kex alg");
1.11 provos 294: if (strcmp(k->name, KEX_DH1) == 0) {
1.51.2.1 margarid 295: k->kex_type = KEX_DH_GRP1_SHA1;
1.11 provos 296: } else if (strcmp(k->name, KEX_DHGEX) == 0) {
1.51.2.1 margarid 297: k->kex_type = KEX_DH_GEX_SHA1;
1.11 provos 298: } else
1.1 markus 299: fatal("bad kex alg %s", k->name);
300: }
1.35 itojun 301: static void
1.1 markus 302: choose_hostkeyalg(Kex *k, char *client, char *server)
303: {
1.23 markus 304: char *hostkeyalg = match_list(client, server, NULL);
1.13 markus 305: if (hostkeyalg == NULL)
1.1 markus 306: fatal("no hostkey alg");
1.13 markus 307: k->hostkey_type = key_type_from_name(hostkeyalg);
308: if (k->hostkey_type == KEY_UNSPEC)
309: fatal("bad hostkey alg '%s'", hostkeyalg);
1.17 markus 310: xfree(hostkeyalg);
1.1 markus 311: }
312:
1.51.2.1 margarid 313: static int
314: proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
315: {
316: static int check[] = {
317: PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
318: };
319: int *idx;
320: char *p;
321:
322: for (idx = &check[0]; *idx != -1; idx++) {
323: if ((p = strchr(my[*idx], ',')) != NULL)
324: *p = '\0';
325: if ((p = strchr(peer[*idx], ',')) != NULL)
326: *p = '\0';
327: if (strcmp(my[*idx], peer[*idx]) != 0) {
328: debug2("proposal mismatch: my %s peer %s",
329: my[*idx], peer[*idx]);
330: return (0);
331: }
332: }
333: debug2("proposals match");
334: return (1);
335: }
336:
1.35 itojun 337: static void
1.27 markus 338: kex_choose_conf(Kex *kex)
1.1 markus 339: {
1.27 markus 340: Newkeys *newkeys;
1.26 markus 341: char **my, **peer;
342: char **cprop, **sprop;
1.27 markus 343: int nenc, nmac, ncomp;
1.1 markus 344: int mode;
345: int ctos; /* direction: if true client-to-server */
346: int need;
1.51.2.1 margarid 347: int first_kex_follows, type;
1.1 markus 348:
1.51.2.1 margarid 349: my = kex_buf2prop(&kex->my, NULL);
350: peer = kex_buf2prop(&kex->peer, &first_kex_follows);
1.26 markus 351:
1.27 markus 352: if (kex->server) {
1.26 markus 353: cprop=peer;
354: sprop=my;
355: } else {
356: cprop=my;
357: sprop=peer;
358: }
1.1 markus 359:
1.30 markus 360: /* Algorithm Negotiation */
1.1 markus 361: for (mode = 0; mode < MODE_MAX; mode++) {
1.27 markus 362: newkeys = xmalloc(sizeof(*newkeys));
363: memset(newkeys, 0, sizeof(*newkeys));
1.30 markus 364: kex->newkeys[mode] = newkeys;
1.27 markus 365: ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
1.1 markus 366: nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
367: nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
368: ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
1.27 markus 369: choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
370: choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
371: choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
1.2 markus 372: debug("kex: %s %s %s %s",
1.1 markus 373: ctos ? "client->server" : "server->client",
1.27 markus 374: newkeys->enc.name,
375: newkeys->mac.name,
376: newkeys->comp.name);
1.1 markus 377: }
1.27 markus 378: choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
379: choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
1.1 markus 380: sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
381: need = 0;
382: for (mode = 0; mode < MODE_MAX; mode++) {
1.30 markus 383: newkeys = kex->newkeys[mode];
1.45 markus 384: if (need < newkeys->enc.key_len)
385: need = newkeys->enc.key_len;
386: if (need < newkeys->enc.block_size)
387: need = newkeys->enc.block_size;
1.27 markus 388: if (need < newkeys->mac.key_len)
389: need = newkeys->mac.key_len;
1.1 markus 390: }
1.7 markus 391: /* XXX need runden? */
1.27 markus 392: kex->we_need = need;
1.26 markus 393:
1.51.2.1 margarid 394: /* ignore the next message if the proposals do not match */
1.51.2.2 margarid 395: if (first_kex_follows && !proposals_match(my, peer) &&
396: !(datafellows & SSH_BUG_FIRSTKEX)) {
1.51.2.1 margarid 397: type = packet_read();
398: debug2("skipping next packet (type %u)", type);
399: }
400:
1.26 markus 401: kex_prop_free(my);
402: kex_prop_free(peer);
403: }
404:
1.35 itojun 405: static u_char *
1.27 markus 406: derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
1.26 markus 407: {
408: Buffer b;
1.47 markus 409: const EVP_MD *evp_md = EVP_sha1();
1.26 markus 410: EVP_MD_CTX md;
411: char c = id;
412: int have;
1.43 markus 413: int mdsz = EVP_MD_size(evp_md);
1.30 markus 414: u_char *digest = xmalloc(roundup(need, mdsz));
1.26 markus 415:
416: buffer_init(&b);
417: buffer_put_bignum2(&b, shared_secret);
418:
1.30 markus 419: /* K1 = HASH(K || H || "A" || session_id) */
1.26 markus 420: EVP_DigestInit(&md, evp_md);
1.34 markus 421: if (!(datafellows & SSH_BUG_DERIVEKEY))
422: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
1.30 markus 423: EVP_DigestUpdate(&md, hash, mdsz);
424: EVP_DigestUpdate(&md, &c, 1);
1.27 markus 425: EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
1.26 markus 426: EVP_DigestFinal(&md, digest, NULL);
427:
1.30 markus 428: /*
429: * expand key:
430: * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
431: * Key = K1 || K2 || ... || Kn
432: */
1.26 markus 433: for (have = mdsz; need > have; have += mdsz) {
434: EVP_DigestInit(&md, evp_md);
1.34 markus 435: if (!(datafellows & SSH_BUG_DERIVEKEY))
436: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
1.26 markus 437: EVP_DigestUpdate(&md, hash, mdsz);
438: EVP_DigestUpdate(&md, digest, have);
439: EVP_DigestFinal(&md, digest + have, NULL);
440: }
441: buffer_free(&b);
442: #ifdef DEBUG_KEX
443: fprintf(stderr, "key '%c'== ", c);
444: dump_digest("key", digest, need);
445: #endif
446: return digest;
1.1 markus 447: }
448:
1.30 markus 449: Newkeys *current_keys[MODE_MAX];
1.27 markus 450:
1.23 markus 451: #define NKEYS 6
1.26 markus 452: void
1.27 markus 453: kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
1.1 markus 454: {
1.15 markus 455: u_char *keys[NKEYS];
1.27 markus 456: int i, mode, ctos;
1.1 markus 457:
458: for (i = 0; i < NKEYS; i++)
1.27 markus 459: keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
1.1 markus 460:
1.51.2.1 margarid 461: debug2("kex_derive_keys");
1.1 markus 462: for (mode = 0; mode < MODE_MAX; mode++) {
1.30 markus 463: current_keys[mode] = kex->newkeys[mode];
464: kex->newkeys[mode] = NULL;
1.27 markus 465: ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
1.30 markus 466: current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
467: current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
468: current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
1.1 markus 469: }
1.27 markus 470: }
471:
472: Newkeys *
473: kex_get_newkeys(int mode)
474: {
1.30 markus 475: Newkeys *ret;
476:
477: ret = current_keys[mode];
478: current_keys[mode] = NULL;
479: return ret;
1.1 markus 480: }
1.26 markus 481:
482: #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
483: void
484: dump_digest(char *msg, u_char *digest, int len)
485: {
486: int i;
487:
488: fprintf(stderr, "%s\n", msg);
1.37 deraadt 489: for (i = 0; i< len; i++) {
1.26 markus 490: fprintf(stderr, "%02x", digest[i]);
491: if (i%32 == 31)
492: fprintf(stderr, "\n");
493: else if (i%8 == 7)
494: fprintf(stderr, " ");
495: }
496: fprintf(stderr, "\n");
497: }
498: #endif
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