xref: /freebsd/crypto/openssh/kex.c (revision 6af83ee0d2941d18880b6aaa2b4facd1d30c6106) 
1 /*
2  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
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"
26 RCSID("$OpenBSD: kex.c,v 1.60 2004/06/21 17:36:31 avsm Exp $");
27 
28 #include <openssl/crypto.h>
29 
30 #include "ssh2.h"
31 #include "xmalloc.h"
32 #include "buffer.h"
33 #include "bufaux.h"
34 #include "packet.h"
35 #include "compat.h"
36 #include "cipher.h"
37 #include "kex.h"
38 #include "key.h"
39 #include "log.h"
40 #include "mac.h"
41 #include "match.h"
42 #include "dispatch.h"
43 #include "monitor.h"
44 
45 #define KEX_COOKIE_LEN	16
46 
47 /* prototype */
48 static void kex_kexinit_finish(Kex *);
49 static void kex_choose_conf(Kex *);
50 
51 /* put algorithm proposal into buffer */
52 static void
53 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
54 {
55 	int i;
56 
57 	buffer_clear(b);
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);
64 	for (i = 0; i < PROPOSAL_MAX; i++)
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 */
68 }
69 
70 /* parse buffer and return algorithm proposal */
71 static char **
72 kex_buf2prop(Buffer *raw, int *first_kex_follows)
73 {
74 	Buffer b;
75 	int i;
76 	char **proposal;
77 
78 	proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
79 
80 	buffer_init(&b);
81 	buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
82 	/* skip cookie */
83 	for (i = 0; i < KEX_COOKIE_LEN; i++)
84 		buffer_get_char(&b);
85 	/* extract kex init proposal strings */
86 	for (i = 0; i < PROPOSAL_MAX; i++) {
87 		proposal[i] = buffer_get_string(&b,NULL);
88 		debug2("kex_parse_kexinit: %s", proposal[i]);
89 	}
90 	/* first kex follows / reserved */
91 	i = buffer_get_char(&b);
92 	if (first_kex_follows != NULL)
93 		*first_kex_follows = i;
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;
99 }
100 
101 static void
102 kex_prop_free(char **proposal)
103 {
104 	int i;
105 
106 	for (i = 0; i < PROPOSAL_MAX; i++)
107 		xfree(proposal[i]);
108 	xfree(proposal);
109 }
110 
111 static void
112 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
113 {
114 	error("Hm, kex protocol error: type %d seq %u", type, seq);
115 }
116 
117 static void
118 kex_reset_dispatch(void)
119 {
120 	dispatch_range(SSH2_MSG_TRANSPORT_MIN,
121 	    SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
122 	dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
123 }
124 
125 void
126 kex_finish(Kex *kex)
127 {
128 	kex_reset_dispatch();
129 
130 	packet_start(SSH2_MSG_NEWKEYS);
131 	packet_send();
132 	/* packet_write_wait(); */
133 	debug("SSH2_MSG_NEWKEYS sent");
134 
135 	debug("expecting SSH2_MSG_NEWKEYS");
136 	packet_read_expect(SSH2_MSG_NEWKEYS);
137 	packet_check_eom();
138 	debug("SSH2_MSG_NEWKEYS received");
139 
140 	kex->done = 1;
141 	buffer_clear(&kex->peer);
142 	/* buffer_clear(&kex->my); */
143 	kex->flags &= ~KEX_INIT_SENT;
144 	xfree(kex->name);
145 	kex->name = NULL;
146 }
147 
148 void
149 kex_send_kexinit(Kex *kex)
150 {
151 	u_int32_t rnd = 0;
152 	u_char *cookie;
153 	int i;
154 
155 	if (kex == NULL) {
156 		error("kex_send_kexinit: no kex, cannot rekey");
157 		return;
158 	}
159 	if (kex->flags & KEX_INIT_SENT) {
160 		debug("KEX_INIT_SENT");
161 		return;
162 	}
163 	kex->done = 0;
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 			rnd = arc4random();
172 		cookie[i] = rnd;
173 		rnd >>= 8;
174 	}
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;
180 }
181 
182 void
183 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
184 {
185 	char *ptr;
186 	int dlen;
187 	int i;
188 	Kex *kex = (Kex *)ctxt;
189 
190 	debug("SSH2_MSG_KEXINIT received");
191 	if (kex == NULL)
192 		fatal("kex_input_kexinit: no kex, cannot rekey");
193 
194 	ptr = packet_get_raw(&dlen);
195 	buffer_append(&kex->peer, ptr, dlen);
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));
202 	(void) packet_get_char();
203 	(void) packet_get_int();
204 	packet_check_eom();
205 
206 	kex_kexinit_finish(kex);
207 }
208 
209 Kex *
210 kex_setup(char *proposal[PROPOSAL_MAX])
211 {
212 	Kex *kex;
213 
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);
219 	kex->done = 0;
220 
221 	kex_send_kexinit(kex);					/* we start */
222 	kex_reset_dispatch();
223 
224 	return kex;
225 }
226 
227 static void
228 kex_kexinit_finish(Kex *kex)
229 {
230 	if (!(kex->flags & KEX_INIT_SENT))
231 		kex_send_kexinit(kex);
232 
233 	kex_choose_conf(kex);
234 
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 {
239 		fatal("Unsupported key exchange %d", kex->kex_type);
240 	}
241 }
242 
243 static void
244 choose_enc(Enc *enc, char *client, char *server)
245 {
246 	char *name = match_list(client, server, NULL);
247 	if (name == NULL)
248 		fatal("no matching cipher found: client %s server %s", client, server);
249 	if ((enc->cipher = cipher_by_name(name)) == NULL)
250 		fatal("matching cipher is not supported: %s", name);
251 	enc->name = name;
252 	enc->enabled = 0;
253 	enc->iv = NULL;
254 	enc->key = NULL;
255 	enc->key_len = cipher_keylen(enc->cipher);
256 	enc->block_size = cipher_blocksize(enc->cipher);
257 }
258 static void
259 choose_mac(Mac *mac, char *client, char *server)
260 {
261 	char *name = match_list(client, server, NULL);
262 	if (name == NULL)
263 		fatal("no matching mac found: client %s server %s", client, server);
264 	if (mac_init(mac, name) < 0)
265 		fatal("unsupported mac %s", name);
266 	/* truncate the key */
267 	if (datafellows & SSH_BUG_HMAC)
268 		mac->key_len = 16;
269 	mac->name = name;
270 	mac->key = NULL;
271 	mac->enabled = 0;
272 }
273 static void
274 choose_comp(Comp *comp, char *client, char *server)
275 {
276 	char *name = match_list(client, server, NULL);
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 }
288 static void
289 choose_kex(Kex *k, char *client, char *server)
290 {
291 	k->name = match_list(client, server, NULL);
292 	if (k->name == NULL)
293 		fatal("no kex alg");
294 	if (strcmp(k->name, KEX_DH1) == 0) {
295 		k->kex_type = KEX_DH_GRP1_SHA1;
296 	} else if (strcmp(k->name, KEX_DH14) == 0) {
297 		k->kex_type = KEX_DH_GRP14_SHA1;
298 	} else if (strcmp(k->name, KEX_DHGEX) == 0) {
299 		k->kex_type = KEX_DH_GEX_SHA1;
300 	} else
301 		fatal("bad kex alg %s", k->name);
302 }
303 static void
304 choose_hostkeyalg(Kex *k, char *client, char *server)
305 {
306 	char *hostkeyalg = match_list(client, server, NULL);
307 	if (hostkeyalg == NULL)
308 		fatal("no hostkey alg");
309 	k->hostkey_type = key_type_from_name(hostkeyalg);
310 	if (k->hostkey_type == KEY_UNSPEC)
311 		fatal("bad hostkey alg '%s'", hostkeyalg);
312 	xfree(hostkeyalg);
313 }
314 
315 static int
316 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
317 {
318 	static int check[] = {
319 		PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
320 	};
321 	int *idx;
322 	char *p;
323 
324 	for (idx = &check[0]; *idx != -1; idx++) {
325 		if ((p = strchr(my[*idx], ',')) != NULL)
326 			*p = '\0';
327 		if ((p = strchr(peer[*idx], ',')) != NULL)
328 			*p = '\0';
329 		if (strcmp(my[*idx], peer[*idx]) != 0) {
330 			debug2("proposal mismatch: my %s peer %s",
331 			    my[*idx], peer[*idx]);
332 			return (0);
333 		}
334 	}
335 	debug2("proposals match");
336 	return (1);
337 }
338 
339 static void
340 kex_choose_conf(Kex *kex)
341 {
342 	Newkeys *newkeys;
343 	char **my, **peer;
344 	char **cprop, **sprop;
345 	int nenc, nmac, ncomp;
346 	int mode;
347 	int ctos;				/* direction: if true client-to-server */
348 	int need;
349 	int first_kex_follows, type;
350 
351 	my   = kex_buf2prop(&kex->my, NULL);
352 	peer = kex_buf2prop(&kex->peer, &first_kex_follows);
353 
354 	if (kex->server) {
355 		cprop=peer;
356 		sprop=my;
357 	} else {
358 		cprop=my;
359 		sprop=peer;
360 	}
361 
362 	/* Algorithm Negotiation */
363 	for (mode = 0; mode < MODE_MAX; mode++) {
364 		newkeys = xmalloc(sizeof(*newkeys));
365 		memset(newkeys, 0, sizeof(*newkeys));
366 		kex->newkeys[mode] = newkeys;
367 		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
368 		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
369 		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
370 		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
371 		choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
372 		choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
373 		choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
374 		debug("kex: %s %s %s %s",
375 		    ctos ? "client->server" : "server->client",
376 		    newkeys->enc.name,
377 		    newkeys->mac.name,
378 		    newkeys->comp.name);
379 	}
380 	choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
381 	choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
382 	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
383 	need = 0;
384 	for (mode = 0; mode < MODE_MAX; mode++) {
385 		newkeys = kex->newkeys[mode];
386 		if (need < newkeys->enc.key_len)
387 			need = newkeys->enc.key_len;
388 		if (need < newkeys->enc.block_size)
389 			need = newkeys->enc.block_size;
390 		if (need < newkeys->mac.key_len)
391 			need = newkeys->mac.key_len;
392 	}
393 	/* XXX need runden? */
394 	kex->we_need = need;
395 
396 	/* ignore the next message if the proposals do not match */
397 	if (first_kex_follows && !proposals_match(my, peer) &&
398 	   !(datafellows & SSH_BUG_FIRSTKEX)) {
399 		type = packet_read();
400 		debug2("skipping next packet (type %u)", type);
401 	}
402 
403 	kex_prop_free(my);
404 	kex_prop_free(peer);
405 }
406 
407 static u_char *
408 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
409 {
410 	Buffer b;
411 	const EVP_MD *evp_md = EVP_sha1();
412 	EVP_MD_CTX md;
413 	char c = id;
414 	int have;
415 	int mdsz = EVP_MD_size(evp_md);
416 	u_char *digest = xmalloc(roundup(need, mdsz));
417 
418 	buffer_init(&b);
419 	buffer_put_bignum2(&b, shared_secret);
420 
421 	/* K1 = HASH(K || H || "A" || session_id) */
422 	EVP_DigestInit(&md, evp_md);
423 	if (!(datafellows & SSH_BUG_DERIVEKEY))
424 		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
425 	EVP_DigestUpdate(&md, hash, mdsz);
426 	EVP_DigestUpdate(&md, &c, 1);
427 	EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
428 	EVP_DigestFinal(&md, digest, NULL);
429 
430 	/*
431 	 * expand key:
432 	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
433 	 * Key = K1 || K2 || ... || Kn
434 	 */
435 	for (have = mdsz; need > have; have += mdsz) {
436 		EVP_DigestInit(&md, evp_md);
437 		if (!(datafellows & SSH_BUG_DERIVEKEY))
438 			EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
439 		EVP_DigestUpdate(&md, hash, mdsz);
440 		EVP_DigestUpdate(&md, digest, have);
441 		EVP_DigestFinal(&md, digest + have, NULL);
442 	}
443 	buffer_free(&b);
444 #ifdef DEBUG_KEX
445 	fprintf(stderr, "key '%c'== ", c);
446 	dump_digest("key", digest, need);
447 #endif
448 	return digest;
449 }
450 
451 Newkeys *current_keys[MODE_MAX];
452 
453 #define NKEYS	6
454 void
455 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
456 {
457 	u_char *keys[NKEYS];
458 	int i, mode, ctos;
459 
460 	for (i = 0; i < NKEYS; i++)
461 		keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
462 
463 	debug2("kex_derive_keys");
464 	for (mode = 0; mode < MODE_MAX; mode++) {
465 		current_keys[mode] = kex->newkeys[mode];
466 		kex->newkeys[mode] = NULL;
467 		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
468 		current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
469 		current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
470 		current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
471 	}
472 }
473 
474 Newkeys *
475 kex_get_newkeys(int mode)
476 {
477 	Newkeys *ret;
478 
479 	ret = current_keys[mode];
480 	current_keys[mode] = NULL;
481 	return ret;
482 }
483 
484 void
485 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
486     u_int8_t cookie[8], u_int8_t id[16])
487 {
488 	const EVP_MD *evp_md = EVP_md5();
489 	EVP_MD_CTX md;
490 	u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
491 	int len;
492 
493 	EVP_DigestInit(&md, evp_md);
494 
495 	len = BN_num_bytes(host_modulus);
496 	if (len < (512 / 8) || len > sizeof(nbuf))
497 		fatal("%s: bad host modulus (len %d)", __func__, len);
498 	BN_bn2bin(host_modulus, nbuf);
499 	EVP_DigestUpdate(&md, nbuf, len);
500 
501 	len = BN_num_bytes(server_modulus);
502 	if (len < (512 / 8) || len > sizeof(nbuf))
503 		fatal("%s: bad server modulus (len %d)", __func__, len);
504 	BN_bn2bin(server_modulus, nbuf);
505 	EVP_DigestUpdate(&md, nbuf, len);
506 
507 	EVP_DigestUpdate(&md, cookie, 8);
508 
509 	EVP_DigestFinal(&md, obuf, NULL);
510 	memcpy(id, obuf, 16);
511 
512 	memset(nbuf, 0, sizeof(nbuf));
513 	memset(obuf, 0, sizeof(obuf));
514 	memset(&md, 0, sizeof(md));
515 }
516 
517 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
518 void
519 dump_digest(char *msg, u_char *digest, int len)
520 {
521 	int i;
522 
523 	fprintf(stderr, "%s\n", msg);
524 	for (i = 0; i< len; i++) {
525 		fprintf(stderr, "%02x", digest[i]);
526 		if (i%32 == 31)
527 			fprintf(stderr, "\n");
528 		else if (i%8 == 7)
529 			fprintf(stderr, " ");
530 	}
531 	fprintf(stderr, "\n");
532 }
533 #endif
534