kex.c revision 157016 
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 1.65 2005/11/04 05:15:59 djm 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	u_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	u_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	u_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	u_int i, dlen;
187	Kex *kex = (Kex *)ctxt;
188
189	debug("SSH2_MSG_KEXINIT received");
190	if (kex == NULL)
191		fatal("kex_input_kexinit: no kex, cannot rekey");
192
193	ptr = packet_get_raw(&dlen);
194	buffer_append(&kex->peer, ptr, dlen);
195
196	/* discard packet */
197	for (i = 0; i < KEX_COOKIE_LEN; i++)
198		packet_get_char();
199	for (i = 0; i < PROPOSAL_MAX; i++)
200		xfree(packet_get_string(NULL));
201	(void) packet_get_char();
202	(void) packet_get_int();
203	packet_check_eom();
204
205	kex_kexinit_finish(kex);
206}
207
208Kex *
209kex_setup(char *proposal[PROPOSAL_MAX])
210{
211	Kex *kex;
212
213	kex = xmalloc(sizeof(*kex));
214	memset(kex, 0, sizeof(*kex));
215	buffer_init(&kex->peer);
216	buffer_init(&kex->my);
217	kex_prop2buf(&kex->my, proposal);
218	kex->done = 0;
219
220	kex_send_kexinit(kex);					/* we start */
221	kex_reset_dispatch();
222
223	return kex;
224}
225
226static void
227kex_kexinit_finish(Kex *kex)
228{
229	if (!(kex->flags & KEX_INIT_SENT))
230		kex_send_kexinit(kex);
231
232	kex_choose_conf(kex);
233
234	if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
235	    kex->kex[kex->kex_type] != NULL) {
236		(kex->kex[kex->kex_type])(kex);
237	} else {
238		fatal("Unsupported key exchange %d", kex->kex_type);
239	}
240}
241
242static void
243choose_enc(Enc *enc, char *client, char *server)
244{
245	char *name = match_list(client, server, NULL);
246	if (name == NULL)
247		fatal("no matching cipher found: client %s server %s", client, server);
248	if ((enc->cipher = cipher_by_name(name)) == NULL)
249		fatal("matching cipher is not supported: %s", name);
250	enc->name = name;
251	enc->enabled = 0;
252	enc->iv = NULL;
253	enc->key = NULL;
254	enc->key_len = cipher_keylen(enc->cipher);
255	enc->block_size = cipher_blocksize(enc->cipher);
256}
257static void
258choose_mac(Mac *mac, char *client, char *server)
259{
260	char *name = match_list(client, server, NULL);
261	if (name == NULL)
262		fatal("no matching mac found: client %s server %s", client, server);
263	if (mac_init(mac, name) < 0)
264		fatal("unsupported mac %s", name);
265	/* truncate the key */
266	if (datafellows & SSH_BUG_HMAC)
267		mac->key_len = 16;
268	mac->name = name;
269	mac->key = NULL;
270	mac->enabled = 0;
271}
272static void
273choose_comp(Comp *comp, char *client, char *server)
274{
275	char *name = match_list(client, server, NULL);
276	if (name == NULL)
277		fatal("no matching comp found: client %s server %s", client, server);
278	if (strcmp(name, "zlib@openssh.com") == 0) {
279		comp->type = COMP_DELAYED;
280	} else if (strcmp(name, "zlib") == 0) {
281		comp->type = COMP_ZLIB;
282	} else if (strcmp(name, "none") == 0) {
283		comp->type = COMP_NONE;
284	} else {
285		fatal("unsupported comp %s", name);
286	}
287	comp->name = name;
288}
289static void
290choose_kex(Kex *k, char *client, char *server)
291{
292	k->name = match_list(client, server, NULL);
293	if (k->name == NULL)
294		fatal("no kex alg");
295	if (strcmp(k->name, KEX_DH1) == 0) {
296		k->kex_type = KEX_DH_GRP1_SHA1;
297		k->evp_md = EVP_sha1();
298	} else if (strcmp(k->name, KEX_DH14) == 0) {
299		k->kex_type = KEX_DH_GRP14_SHA1;
300		k->evp_md = EVP_sha1();
301	} else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
302		k->kex_type = KEX_DH_GEX_SHA1;
303		k->evp_md = EVP_sha1();
304	} else
305		fatal("bad kex alg %s", k->name);
306}
307
308static void
309choose_hostkeyalg(Kex *k, char *client, char *server)
310{
311	char *hostkeyalg = match_list(client, server, NULL);
312	if (hostkeyalg == NULL)
313		fatal("no hostkey alg");
314	k->hostkey_type = key_type_from_name(hostkeyalg);
315	if (k->hostkey_type == KEY_UNSPEC)
316		fatal("bad hostkey alg '%s'", hostkeyalg);
317	xfree(hostkeyalg);
318}
319
320static int
321proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
322{
323	static int check[] = {
324		PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
325	};
326	int *idx;
327	char *p;
328
329	for (idx = &check[0]; *idx != -1; idx++) {
330		if ((p = strchr(my[*idx], ',')) != NULL)
331			*p = '\0';
332		if ((p = strchr(peer[*idx], ',')) != NULL)
333			*p = '\0';
334		if (strcmp(my[*idx], peer[*idx]) != 0) {
335			debug2("proposal mismatch: my %s peer %s",
336			    my[*idx], peer[*idx]);
337			return (0);
338		}
339	}
340	debug2("proposals match");
341	return (1);
342}
343
344static void
345kex_choose_conf(Kex *kex)
346{
347	Newkeys *newkeys;
348	char **my, **peer;
349	char **cprop, **sprop;
350	int nenc, nmac, ncomp;
351	u_int mode, ctos, need;
352	int first_kex_follows, type;
353
354	my   = kex_buf2prop(&kex->my, NULL);
355	peer = kex_buf2prop(&kex->peer, &first_kex_follows);
356
357	if (kex->server) {
358		cprop=peer;
359		sprop=my;
360	} else {
361		cprop=my;
362		sprop=peer;
363	}
364
365	/* Algorithm Negotiation */
366	for (mode = 0; mode < MODE_MAX; mode++) {
367		newkeys = xmalloc(sizeof(*newkeys));
368		memset(newkeys, 0, sizeof(*newkeys));
369		kex->newkeys[mode] = newkeys;
370		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
371		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
372		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
373		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
374		choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
375		choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
376		choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
377		debug("kex: %s %s %s %s",
378		    ctos ? "client->server" : "server->client",
379		    newkeys->enc.name,
380		    newkeys->mac.name,
381		    newkeys->comp.name);
382	}
383	choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
384	choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
385	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
386	need = 0;
387	for (mode = 0; mode < MODE_MAX; mode++) {
388		newkeys = kex->newkeys[mode];
389		if (need < newkeys->enc.key_len)
390			need = newkeys->enc.key_len;
391		if (need < newkeys->enc.block_size)
392			need = newkeys->enc.block_size;
393		if (need < newkeys->mac.key_len)
394			need = newkeys->mac.key_len;
395	}
396	/* XXX need runden? */
397	kex->we_need = need;
398
399	/* ignore the next message if the proposals do not match */
400	if (first_kex_follows && !proposals_match(my, peer) &&
401	    !(datafellows & SSH_BUG_FIRSTKEX)) {
402		type = packet_read();
403		debug2("skipping next packet (type %u)", type);
404	}
405
406	kex_prop_free(my);
407	kex_prop_free(peer);
408}
409
410static u_char *
411derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
412    BIGNUM *shared_secret)
413{
414	Buffer b;
415	EVP_MD_CTX md;
416	char c = id;
417	u_int have;
418	int mdsz;
419	u_char *digest;
420
421	if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
422		fatal("bad kex md size %d", mdsz);
423 	digest = xmalloc(roundup(need, mdsz));
424
425	buffer_init(&b);
426	buffer_put_bignum2(&b, shared_secret);
427
428	/* K1 = HASH(K || H || "A" || session_id) */
429	EVP_DigestInit(&md, kex->evp_md);
430	if (!(datafellows & SSH_BUG_DERIVEKEY))
431		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
432	EVP_DigestUpdate(&md, hash, hashlen);
433	EVP_DigestUpdate(&md, &c, 1);
434	EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
435	EVP_DigestFinal(&md, digest, NULL);
436
437	/*
438	 * expand key:
439	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
440	 * Key = K1 || K2 || ... || Kn
441	 */
442	for (have = mdsz; need > have; have += mdsz) {
443		EVP_DigestInit(&md, kex->evp_md);
444		if (!(datafellows & SSH_BUG_DERIVEKEY))
445			EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
446		EVP_DigestUpdate(&md, hash, hashlen);
447		EVP_DigestUpdate(&md, digest, have);
448		EVP_DigestFinal(&md, digest + have, NULL);
449	}
450	buffer_free(&b);
451#ifdef DEBUG_KEX
452	fprintf(stderr, "key '%c'== ", c);
453	dump_digest("key", digest, need);
454#endif
455	return digest;
456}
457
458Newkeys *current_keys[MODE_MAX];
459
460#define NKEYS	6
461void
462kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
463{
464	u_char *keys[NKEYS];
465	u_int i, mode, ctos;
466
467	for (i = 0; i < NKEYS; i++) {
468		keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
469		    shared_secret);
470	}
471
472	debug2("kex_derive_keys");
473	for (mode = 0; mode < MODE_MAX; mode++) {
474		current_keys[mode] = kex->newkeys[mode];
475		kex->newkeys[mode] = NULL;
476		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
477		current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
478		current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
479		current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
480	}
481}
482
483Newkeys *
484kex_get_newkeys(int mode)
485{
486	Newkeys *ret;
487
488	ret = current_keys[mode];
489	current_keys[mode] = NULL;
490	return ret;
491}
492
493void
494derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
495    u_int8_t cookie[8], u_int8_t id[16])
496{
497	const EVP_MD *evp_md = EVP_md5();
498	EVP_MD_CTX md;
499	u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
500	int len;
501
502	EVP_DigestInit(&md, evp_md);
503
504	len = BN_num_bytes(host_modulus);
505	if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
506		fatal("%s: bad host modulus (len %d)", __func__, len);
507	BN_bn2bin(host_modulus, nbuf);
508	EVP_DigestUpdate(&md, nbuf, len);
509
510	len = BN_num_bytes(server_modulus);
511	if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
512		fatal("%s: bad server modulus (len %d)", __func__, len);
513	BN_bn2bin(server_modulus, nbuf);
514	EVP_DigestUpdate(&md, nbuf, len);
515
516	EVP_DigestUpdate(&md, cookie, 8);
517
518	EVP_DigestFinal(&md, obuf, NULL);
519	memcpy(id, obuf, 16);
520
521	memset(nbuf, 0, sizeof(nbuf));
522	memset(obuf, 0, sizeof(obuf));
523	memset(&md, 0, sizeof(md));
524}
525
526#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
527void
528dump_digest(char *msg, u_char *digest, int len)
529{
530	u_int i;
531
532	fprintf(stderr, "%s\n", msg);
533	for (i = 0; i< len; i++) {
534		fprintf(stderr, "%02x", digest[i]);
535		if (i%32 == 31)
536			fprintf(stderr, "\n");
537		else if (i%8 == 7)
538			fprintf(stderr, " ");
539	}
540	fprintf(stderr, "\n");
541}
542#endif
543