kex.c revision 137015 
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"
26RCSID("$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 */
48static void kex_kexinit_finish(Kex *);
49static void kex_choose_conf(Kex *);
50
51/* put algorithm proposal into buffer */
52static void
53kex_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 */
71static char **
72kex_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
101static void
102kex_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
111static void
112kex_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
117static void
118kex_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
125void
126kex_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
148void
149kex_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
182void
183kex_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
209Kex *
210kex_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
227static void
228kex_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
243static void
244choose_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}
258static void
259choose_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}
273static void
274choose_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}
288static void
289choose_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}
303static void
304choose_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
315static int
316proposals_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
339static void
340kex_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
407static u_char *
408derive_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
451Newkeys *current_keys[MODE_MAX];
452
453#define NKEYS	6
454void
455kex_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
474Newkeys *
475kex_get_newkeys(int mode)
476{
477	Newkeys *ret;
478
479	ret = current_keys[mode];
480	current_keys[mode] = NULL;
481	return ret;
482}
483
484void
485derive_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)
518void
519dump_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