kex.c revision 113908 
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 1.55 2003/04/01 10:31:26 markus 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 rand = 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			rand = arc4random();
172		cookie[i] = rand;
173		rand >>= 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_DHGEX) == 0) {
297		k->kex_type = KEX_DH_GEX_SHA1;
298	} else
299		fatal("bad kex alg %s", k->name);
300}
301static void
302choose_hostkeyalg(Kex *k, char *client, char *server)
303{
304	char *hostkeyalg = match_list(client, server, NULL);
305	if (hostkeyalg == NULL)
306		fatal("no hostkey alg");
307	k->hostkey_type = key_type_from_name(hostkeyalg);
308	if (k->hostkey_type == KEY_UNSPEC)
309		fatal("bad hostkey alg '%s'", hostkeyalg);
310	xfree(hostkeyalg);
311}
312
313static int
314proposals_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
337static void
338kex_choose_conf(Kex *kex)
339{
340	Newkeys *newkeys;
341	char **my, **peer;
342	char **cprop, **sprop;
343	int nenc, nmac, ncomp;
344	int mode;
345	int ctos;				/* direction: if true client-to-server */
346	int need;
347	int first_kex_follows, type;
348
349	my   = kex_buf2prop(&kex->my, NULL);
350	peer = kex_buf2prop(&kex->peer, &first_kex_follows);
351
352	if (kex->server) {
353		cprop=peer;
354		sprop=my;
355	} else {
356		cprop=my;
357		sprop=peer;
358	}
359
360	/* Algorithm Negotiation */
361	for (mode = 0; mode < MODE_MAX; mode++) {
362		newkeys = xmalloc(sizeof(*newkeys));
363		memset(newkeys, 0, sizeof(*newkeys));
364		kex->newkeys[mode] = newkeys;
365		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
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;
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]);
372		debug("kex: %s %s %s %s",
373		    ctos ? "client->server" : "server->client",
374		    newkeys->enc.name,
375		    newkeys->mac.name,
376		    newkeys->comp.name);
377	}
378	choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
379	choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
380	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
381	need = 0;
382	for (mode = 0; mode < MODE_MAX; mode++) {
383		newkeys = kex->newkeys[mode];
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;
388		if (need < newkeys->mac.key_len)
389			need = newkeys->mac.key_len;
390	}
391	/* XXX need runden? */
392	kex->we_need = need;
393
394	/* ignore the next message if the proposals do not match */
395	if (first_kex_follows && !proposals_match(my, peer) &&
396	   !(datafellows & SSH_BUG_FIRSTKEX)) {
397		type = packet_read();
398		debug2("skipping next packet (type %u)", type);
399	}
400
401	kex_prop_free(my);
402	kex_prop_free(peer);
403}
404
405static u_char *
406derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
407{
408	Buffer b;
409	const EVP_MD *evp_md = EVP_sha1();
410	EVP_MD_CTX md;
411	char c = id;
412	int have;
413	int mdsz = EVP_MD_size(evp_md);
414	u_char *digest = xmalloc(roundup(need, mdsz));
415
416	buffer_init(&b);
417	buffer_put_bignum2(&b, shared_secret);
418
419	/* K1 = HASH(K || H || "A" || session_id) */
420	EVP_DigestInit(&md, evp_md);
421	if (!(datafellows & SSH_BUG_DERIVEKEY))
422		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
423	EVP_DigestUpdate(&md, hash, mdsz);
424	EVP_DigestUpdate(&md, &c, 1);
425	EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
426	EVP_DigestFinal(&md, digest, NULL);
427
428	/*
429	 * expand key:
430	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
431	 * Key = K1 || K2 || ... || Kn
432	 */
433	for (have = mdsz; need > have; have += mdsz) {
434		EVP_DigestInit(&md, evp_md);
435		if (!(datafellows & SSH_BUG_DERIVEKEY))
436			EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
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;
447}
448
449Newkeys *current_keys[MODE_MAX];
450
451#define NKEYS	6
452void
453kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
454{
455	u_char *keys[NKEYS];
456	int i, mode, ctos;
457
458	for (i = 0; i < NKEYS; i++)
459		keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
460
461	debug2("kex_derive_keys");
462	for (mode = 0; mode < MODE_MAX; mode++) {
463		current_keys[mode] = kex->newkeys[mode];
464		kex->newkeys[mode] = NULL;
465		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
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];
469	}
470}
471
472Newkeys *
473kex_get_newkeys(int mode)
474{
475	Newkeys *ret;
476
477	ret = current_keys[mode];
478	current_keys[mode] = NULL;
479	return ret;
480}
481
482#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
483void
484dump_digest(char *msg, u_char *digest, int len)
485{
486	int i;
487
488	fprintf(stderr, "%s\n", msg);
489	for (i = 0; i< len; i++) {
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
499