kex.c revision 197679 
1/* $OpenBSD: kex.c,v 1.81 2009/05/27 06:34:36 andreas Exp $ */
2/*
3 * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#include "includes.h"
27
28#include <sys/param.h>
29
30#include <signal.h>
31#include <stdarg.h>
32#include <stdio.h>
33#include <stdlib.h>
34#include <string.h>
35
36#include <openssl/crypto.h>
37
38#include "xmalloc.h"
39#include "ssh2.h"
40#include "buffer.h"
41#include "packet.h"
42#include "compat.h"
43#include "cipher.h"
44#include "key.h"
45#include "kex.h"
46#include "log.h"
47#include "mac.h"
48#include "match.h"
49#include "dispatch.h"
50#include "monitor.h"
51
52#if OPENSSL_VERSION_NUMBER >= 0x00907000L
53# if defined(HAVE_EVP_SHA256)
54# define evp_ssh_sha256 EVP_sha256
55# else
56extern const EVP_MD *evp_ssh_sha256(void);
57# endif
58#endif
59
60/* prototype */
61static void kex_kexinit_finish(Kex *);
62static void kex_choose_conf(Kex *);
63
64/* put algorithm proposal into buffer */
65static void
66kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
67{
68	u_int i;
69
70	buffer_clear(b);
71	/*
72	 * add a dummy cookie, the cookie will be overwritten by
73	 * kex_send_kexinit(), each time a kexinit is set
74	 */
75	for (i = 0; i < KEX_COOKIE_LEN; i++)
76		buffer_put_char(b, 0);
77	for (i = 0; i < PROPOSAL_MAX; i++)
78		buffer_put_cstring(b, proposal[i]);
79	buffer_put_char(b, 0);			/* first_kex_packet_follows */
80	buffer_put_int(b, 0);			/* uint32 reserved */
81}
82
83/* parse buffer and return algorithm proposal */
84static char **
85kex_buf2prop(Buffer *raw, int *first_kex_follows)
86{
87	Buffer b;
88	u_int i;
89	char **proposal;
90
91	proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
92
93	buffer_init(&b);
94	buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
95	/* skip cookie */
96	for (i = 0; i < KEX_COOKIE_LEN; i++)
97		buffer_get_char(&b);
98	/* extract kex init proposal strings */
99	for (i = 0; i < PROPOSAL_MAX; i++) {
100		proposal[i] = buffer_get_string(&b,NULL);
101		debug2("kex_parse_kexinit: %s", proposal[i]);
102	}
103	/* first kex follows / reserved */
104	i = buffer_get_char(&b);
105	if (first_kex_follows != NULL)
106		*first_kex_follows = i;
107	debug2("kex_parse_kexinit: first_kex_follows %d ", i);
108	i = buffer_get_int(&b);
109	debug2("kex_parse_kexinit: reserved %u ", i);
110	buffer_free(&b);
111	return proposal;
112}
113
114static void
115kex_prop_free(char **proposal)
116{
117	u_int i;
118
119	for (i = 0; i < PROPOSAL_MAX; i++)
120		xfree(proposal[i]);
121	xfree(proposal);
122}
123
124/* ARGSUSED */
125static void
126kex_protocol_error(int type, u_int32_t seq, void *ctxt)
127{
128	error("Hm, kex protocol error: type %d seq %u", type, seq);
129}
130
131static void
132kex_reset_dispatch(void)
133{
134	dispatch_range(SSH2_MSG_TRANSPORT_MIN,
135	    SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
136	dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
137}
138
139void
140kex_finish(Kex *kex)
141{
142	kex_reset_dispatch();
143
144	packet_start(SSH2_MSG_NEWKEYS);
145	packet_send();
146	/* packet_write_wait(); */
147	debug("SSH2_MSG_NEWKEYS sent");
148
149	debug("expecting SSH2_MSG_NEWKEYS");
150	packet_read_expect(SSH2_MSG_NEWKEYS);
151	packet_check_eom();
152	debug("SSH2_MSG_NEWKEYS received");
153
154	kex->done = 1;
155	buffer_clear(&kex->peer);
156	/* buffer_clear(&kex->my); */
157	kex->flags &= ~KEX_INIT_SENT;
158	xfree(kex->name);
159	kex->name = NULL;
160}
161
162void
163kex_send_kexinit(Kex *kex)
164{
165	u_int32_t rnd = 0;
166	u_char *cookie;
167	u_int i;
168
169	if (kex == NULL) {
170		error("kex_send_kexinit: no kex, cannot rekey");
171		return;
172	}
173	if (kex->flags & KEX_INIT_SENT) {
174		debug("KEX_INIT_SENT");
175		return;
176	}
177	kex->done = 0;
178
179	/* generate a random cookie */
180	if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
181		fatal("kex_send_kexinit: kex proposal too short");
182	cookie = buffer_ptr(&kex->my);
183	for (i = 0; i < KEX_COOKIE_LEN; i++) {
184		if (i % 4 == 0)
185			rnd = arc4random();
186		cookie[i] = rnd;
187		rnd >>= 8;
188	}
189	packet_start(SSH2_MSG_KEXINIT);
190	packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
191	packet_send();
192	debug("SSH2_MSG_KEXINIT sent");
193	kex->flags |= KEX_INIT_SENT;
194}
195
196/* ARGSUSED */
197void
198kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
199{
200	char *ptr;
201	u_int i, dlen;
202	Kex *kex = (Kex *)ctxt;
203
204	debug("SSH2_MSG_KEXINIT received");
205	if (kex == NULL)
206		fatal("kex_input_kexinit: no kex, cannot rekey");
207
208	ptr = packet_get_raw(&dlen);
209	buffer_append(&kex->peer, ptr, dlen);
210
211	/* discard packet */
212	for (i = 0; i < KEX_COOKIE_LEN; i++)
213		packet_get_char();
214	for (i = 0; i < PROPOSAL_MAX; i++)
215		xfree(packet_get_string(NULL));
216	(void) packet_get_char();
217	(void) packet_get_int();
218	packet_check_eom();
219
220	kex_kexinit_finish(kex);
221}
222
223Kex *
224kex_setup(char *proposal[PROPOSAL_MAX])
225{
226	Kex *kex;
227
228	kex = xcalloc(1, sizeof(*kex));
229	buffer_init(&kex->peer);
230	buffer_init(&kex->my);
231	kex_prop2buf(&kex->my, proposal);
232	kex->done = 0;
233
234	kex_send_kexinit(kex);					/* we start */
235	kex_reset_dispatch();
236
237	return kex;
238}
239
240static void
241kex_kexinit_finish(Kex *kex)
242{
243	if (!(kex->flags & KEX_INIT_SENT))
244		kex_send_kexinit(kex);
245
246	kex_choose_conf(kex);
247
248	if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
249	    kex->kex[kex->kex_type] != NULL) {
250		(kex->kex[kex->kex_type])(kex);
251	} else {
252		fatal("Unsupported key exchange %d", kex->kex_type);
253	}
254}
255
256static void
257choose_enc(Enc *enc, char *client, char *server)
258{
259	char *name = match_list(client, server, NULL);
260	if (name == NULL)
261		fatal("no matching cipher found: client %s server %s",
262		    client, server);
263	if ((enc->cipher = cipher_by_name(name)) == NULL)
264		fatal("matching cipher is not supported: %s", name);
265	enc->name = name;
266	enc->enabled = 0;
267	enc->iv = NULL;
268	enc->key = NULL;
269	enc->key_len = cipher_keylen(enc->cipher);
270	enc->block_size = cipher_blocksize(enc->cipher);
271}
272
273static void
274choose_mac(Mac *mac, char *client, char *server)
275{
276	char *name = match_list(client, server, NULL);
277	if (name == NULL)
278		fatal("no matching mac found: client %s server %s",
279		    client, server);
280	if (mac_setup(mac, name) < 0)
281		fatal("unsupported mac %s", name);
282	/* truncate the key */
283	if (datafellows & SSH_BUG_HMAC)
284		mac->key_len = 16;
285	mac->name = name;
286	mac->key = NULL;
287	mac->enabled = 0;
288}
289
290static void
291choose_comp(Comp *comp, char *client, char *server)
292{
293	char *name = match_list(client, server, NULL);
294	if (name == NULL)
295		fatal("no matching comp found: client %s server %s", client, server);
296	if (strcmp(name, "zlib@openssh.com") == 0) {
297		comp->type = COMP_DELAYED;
298	} else if (strcmp(name, "zlib") == 0) {
299		comp->type = COMP_ZLIB;
300	} else if (strcmp(name, "none") == 0) {
301		comp->type = COMP_NONE;
302	} else {
303		fatal("unsupported comp %s", name);
304	}
305	comp->name = name;
306}
307
308static void
309choose_kex(Kex *k, char *client, char *server)
310{
311	k->name = match_list(client, server, NULL);
312	if (k->name == NULL)
313		fatal("Unable to negotiate a key exchange method");
314	if (strcmp(k->name, KEX_DH1) == 0) {
315		k->kex_type = KEX_DH_GRP1_SHA1;
316		k->evp_md = EVP_sha1();
317	} else if (strcmp(k->name, KEX_DH14) == 0) {
318		k->kex_type = KEX_DH_GRP14_SHA1;
319		k->evp_md = EVP_sha1();
320	} else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
321		k->kex_type = KEX_DH_GEX_SHA1;
322		k->evp_md = EVP_sha1();
323#if OPENSSL_VERSION_NUMBER >= 0x00907000L
324	} else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
325		k->kex_type = KEX_DH_GEX_SHA256;
326		k->evp_md = evp_ssh_sha256();
327#endif
328	} else
329		fatal("bad kex alg %s", k->name);
330}
331
332static void
333choose_hostkeyalg(Kex *k, char *client, char *server)
334{
335	char *hostkeyalg = match_list(client, server, NULL);
336	if (hostkeyalg == NULL)
337		fatal("no hostkey alg");
338	k->hostkey_type = key_type_from_name(hostkeyalg);
339	if (k->hostkey_type == KEY_UNSPEC)
340		fatal("bad hostkey alg '%s'", hostkeyalg);
341	xfree(hostkeyalg);
342}
343
344static int
345proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
346{
347	static int check[] = {
348		PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
349	};
350	int *idx;
351	char *p;
352
353	for (idx = &check[0]; *idx != -1; idx++) {
354		if ((p = strchr(my[*idx], ',')) != NULL)
355			*p = '\0';
356		if ((p = strchr(peer[*idx], ',')) != NULL)
357			*p = '\0';
358		if (strcmp(my[*idx], peer[*idx]) != 0) {
359			debug2("proposal mismatch: my %s peer %s",
360			    my[*idx], peer[*idx]);
361			return (0);
362		}
363	}
364	debug2("proposals match");
365	return (1);
366}
367
368static void
369kex_choose_conf(Kex *kex)
370{
371	Newkeys *newkeys;
372	char **my, **peer;
373	char **cprop, **sprop;
374	int nenc, nmac, ncomp;
375	u_int mode, ctos, need;
376	int first_kex_follows, type;
377
378	my   = kex_buf2prop(&kex->my, NULL);
379	peer = kex_buf2prop(&kex->peer, &first_kex_follows);
380
381	if (kex->server) {
382		cprop=peer;
383		sprop=my;
384	} else {
385		cprop=my;
386		sprop=peer;
387	}
388
389	/* Algorithm Negotiation */
390	for (mode = 0; mode < MODE_MAX; mode++) {
391		newkeys = xcalloc(1, sizeof(*newkeys));
392		kex->newkeys[mode] = newkeys;
393		ctos = (!kex->server && mode == MODE_OUT) ||
394		    (kex->server && mode == MODE_IN);
395		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
396		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
397		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
398		choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
399		choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
400		choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
401		debug("kex: %s %s %s %s",
402		    ctos ? "client->server" : "server->client",
403		    newkeys->enc.name,
404		    newkeys->mac.name,
405		    newkeys->comp.name);
406	}
407	choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
408	choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
409	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
410	need = 0;
411	for (mode = 0; mode < MODE_MAX; mode++) {
412		newkeys = kex->newkeys[mode];
413		if (need < newkeys->enc.key_len)
414			need = newkeys->enc.key_len;
415		if (need < newkeys->enc.block_size)
416			need = newkeys->enc.block_size;
417		if (need < newkeys->mac.key_len)
418			need = newkeys->mac.key_len;
419	}
420	/* XXX need runden? */
421	kex->we_need = need;
422
423	/* ignore the next message if the proposals do not match */
424	if (first_kex_follows && !proposals_match(my, peer) &&
425	    !(datafellows & SSH_BUG_FIRSTKEX)) {
426		type = packet_read();
427		debug2("skipping next packet (type %u)", type);
428	}
429
430	kex_prop_free(my);
431	kex_prop_free(peer);
432}
433
434static u_char *
435derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
436    BIGNUM *shared_secret)
437{
438	Buffer b;
439	EVP_MD_CTX md;
440	char c = id;
441	u_int have;
442	int mdsz;
443	u_char *digest;
444
445	if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
446		fatal("bad kex md size %d", mdsz);
447	digest = xmalloc(roundup(need, mdsz));
448
449	buffer_init(&b);
450	buffer_put_bignum2(&b, shared_secret);
451
452	/* K1 = HASH(K || H || "A" || session_id) */
453	EVP_DigestInit(&md, kex->evp_md);
454	if (!(datafellows & SSH_BUG_DERIVEKEY))
455		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
456	EVP_DigestUpdate(&md, hash, hashlen);
457	EVP_DigestUpdate(&md, &c, 1);
458	EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
459	EVP_DigestFinal(&md, digest, NULL);
460
461	/*
462	 * expand key:
463	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
464	 * Key = K1 || K2 || ... || Kn
465	 */
466	for (have = mdsz; need > have; have += mdsz) {
467		EVP_DigestInit(&md, kex->evp_md);
468		if (!(datafellows & SSH_BUG_DERIVEKEY))
469			EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
470		EVP_DigestUpdate(&md, hash, hashlen);
471		EVP_DigestUpdate(&md, digest, have);
472		EVP_DigestFinal(&md, digest + have, NULL);
473	}
474	buffer_free(&b);
475#ifdef DEBUG_KEX
476	fprintf(stderr, "key '%c'== ", c);
477	dump_digest("key", digest, need);
478#endif
479	return digest;
480}
481
482Newkeys *current_keys[MODE_MAX];
483
484#define NKEYS	6
485void
486kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
487{
488	u_char *keys[NKEYS];
489	u_int i, mode, ctos;
490
491	for (i = 0; i < NKEYS; i++) {
492		keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
493		    shared_secret);
494	}
495
496	debug2("kex_derive_keys");
497	for (mode = 0; mode < MODE_MAX; mode++) {
498		current_keys[mode] = kex->newkeys[mode];
499		kex->newkeys[mode] = NULL;
500		ctos = (!kex->server && mode == MODE_OUT) ||
501		    (kex->server && mode == MODE_IN);
502		current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
503		current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
504		current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
505	}
506}
507
508Newkeys *
509kex_get_newkeys(int mode)
510{
511	Newkeys *ret;
512
513	ret = current_keys[mode];
514	current_keys[mode] = NULL;
515	return ret;
516}
517
518void
519derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
520    u_int8_t cookie[8], u_int8_t id[16])
521{
522	const EVP_MD *evp_md = EVP_md5();
523	EVP_MD_CTX md;
524	u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
525	int len;
526
527	EVP_DigestInit(&md, evp_md);
528
529	len = BN_num_bytes(host_modulus);
530	if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
531		fatal("%s: bad host modulus (len %d)", __func__, len);
532	BN_bn2bin(host_modulus, nbuf);
533	EVP_DigestUpdate(&md, nbuf, len);
534
535	len = BN_num_bytes(server_modulus);
536	if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
537		fatal("%s: bad server modulus (len %d)", __func__, len);
538	BN_bn2bin(server_modulus, nbuf);
539	EVP_DigestUpdate(&md, nbuf, len);
540
541	EVP_DigestUpdate(&md, cookie, 8);
542
543	EVP_DigestFinal(&md, obuf, NULL);
544	memcpy(id, obuf, 16);
545
546	memset(nbuf, 0, sizeof(nbuf));
547	memset(obuf, 0, sizeof(obuf));
548	memset(&md, 0, sizeof(md));
549}
550
551#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
552void
553dump_digest(char *msg, u_char *digest, int len)
554{
555	u_int i;
556
557	fprintf(stderr, "%s\n", msg);
558	for (i = 0; i < len; i++) {
559		fprintf(stderr, "%02x", digest[i]);
560		if (i%32 == 31)
561			fprintf(stderr, "\n");
562		else if (i%8 == 7)
563			fprintf(stderr, " ");
564	}
565	fprintf(stderr, "\n");
566}
567#endif
568