kex.c revision 192595 
1/* $OpenBSD: kex.c,v 1.80 2008/09/06 12:24:13 djm 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#define KEX_COOKIE_LEN	16
53
54#if OPENSSL_VERSION_NUMBER >= 0x00907000L
55# if defined(HAVE_EVP_SHA256)
56# define evp_ssh_sha256 EVP_sha256
57# else
58extern const EVP_MD *evp_ssh_sha256(void);
59# endif
60#endif
61
62/* prototype */
63static void kex_kexinit_finish(Kex *);
64static void kex_choose_conf(Kex *);
65
66/* put algorithm proposal into buffer */
67static void
68kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
69{
70	u_int i;
71
72	buffer_clear(b);
73	/*
74	 * add a dummy cookie, the cookie will be overwritten by
75	 * kex_send_kexinit(), each time a kexinit is set
76	 */
77	for (i = 0; i < KEX_COOKIE_LEN; i++)
78		buffer_put_char(b, 0);
79	for (i = 0; i < PROPOSAL_MAX; i++)
80		buffer_put_cstring(b, proposal[i]);
81	buffer_put_char(b, 0);			/* first_kex_packet_follows */
82	buffer_put_int(b, 0);			/* uint32 reserved */
83}
84
85/* parse buffer and return algorithm proposal */
86static char **
87kex_buf2prop(Buffer *raw, int *first_kex_follows)
88{
89	Buffer b;
90	u_int i;
91	char **proposal;
92
93	proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
94
95	buffer_init(&b);
96	buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
97	/* skip cookie */
98	for (i = 0; i < KEX_COOKIE_LEN; i++)
99		buffer_get_char(&b);
100	/* extract kex init proposal strings */
101	for (i = 0; i < PROPOSAL_MAX; i++) {
102		proposal[i] = buffer_get_string(&b,NULL);
103		debug2("kex_parse_kexinit: %s", proposal[i]);
104	}
105	/* first kex follows / reserved */
106	i = buffer_get_char(&b);
107	if (first_kex_follows != NULL)
108		*first_kex_follows = i;
109	debug2("kex_parse_kexinit: first_kex_follows %d ", i);
110	i = buffer_get_int(&b);
111	debug2("kex_parse_kexinit: reserved %u ", i);
112	buffer_free(&b);
113	return proposal;
114}
115
116static void
117kex_prop_free(char **proposal)
118{
119	u_int i;
120
121	for (i = 0; i < PROPOSAL_MAX; i++)
122		xfree(proposal[i]);
123	xfree(proposal);
124}
125
126/* ARGSUSED */
127static void
128kex_protocol_error(int type, u_int32_t seq, void *ctxt)
129{
130	error("Hm, kex protocol error: type %d seq %u", type, seq);
131}
132
133static void
134kex_reset_dispatch(void)
135{
136	dispatch_range(SSH2_MSG_TRANSPORT_MIN,
137	    SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
138	dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
139}
140
141void
142kex_finish(Kex *kex)
143{
144	kex_reset_dispatch();
145
146	packet_start(SSH2_MSG_NEWKEYS);
147	packet_send();
148	/* packet_write_wait(); */
149	debug("SSH2_MSG_NEWKEYS sent");
150
151	debug("expecting SSH2_MSG_NEWKEYS");
152	packet_read_expect(SSH2_MSG_NEWKEYS);
153	packet_check_eom();
154	debug("SSH2_MSG_NEWKEYS received");
155
156	kex->done = 1;
157	buffer_clear(&kex->peer);
158	/* buffer_clear(&kex->my); */
159	kex->flags &= ~KEX_INIT_SENT;
160	xfree(kex->name);
161	kex->name = NULL;
162}
163
164void
165kex_send_kexinit(Kex *kex)
166{
167	u_int32_t rnd = 0;
168	u_char *cookie;
169	u_int i;
170
171	if (kex == NULL) {
172		error("kex_send_kexinit: no kex, cannot rekey");
173		return;
174	}
175	if (kex->flags & KEX_INIT_SENT) {
176		debug("KEX_INIT_SENT");
177		return;
178	}
179	kex->done = 0;
180
181	/* generate a random cookie */
182	if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
183		fatal("kex_send_kexinit: kex proposal too short");
184	cookie = buffer_ptr(&kex->my);
185	for (i = 0; i < KEX_COOKIE_LEN; i++) {
186		if (i % 4 == 0)
187			rnd = arc4random();
188		cookie[i] = rnd;
189		rnd >>= 8;
190	}
191	packet_start(SSH2_MSG_KEXINIT);
192	packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
193	packet_send();
194	debug("SSH2_MSG_KEXINIT sent");
195	kex->flags |= KEX_INIT_SENT;
196}
197
198/* ARGSUSED */
199void
200kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
201{
202	char *ptr;
203	u_int i, dlen;
204	Kex *kex = (Kex *)ctxt;
205
206	debug("SSH2_MSG_KEXINIT received");
207	if (kex == NULL)
208		fatal("kex_input_kexinit: no kex, cannot rekey");
209
210	ptr = packet_get_raw(&dlen);
211	buffer_append(&kex->peer, ptr, dlen);
212
213	/* discard packet */
214	for (i = 0; i < KEX_COOKIE_LEN; i++)
215		packet_get_char();
216	for (i = 0; i < PROPOSAL_MAX; i++)
217		xfree(packet_get_string(NULL));
218	(void) packet_get_char();
219	(void) packet_get_int();
220	packet_check_eom();
221
222	kex_kexinit_finish(kex);
223}
224
225Kex *
226kex_setup(char *proposal[PROPOSAL_MAX])
227{
228	Kex *kex;
229
230	kex = xcalloc(1, sizeof(*kex));
231	buffer_init(&kex->peer);
232	buffer_init(&kex->my);
233	kex_prop2buf(&kex->my, proposal);
234	kex->done = 0;
235
236	kex_send_kexinit(kex);					/* we start */
237	kex_reset_dispatch();
238
239	return kex;
240}
241
242static void
243kex_kexinit_finish(Kex *kex)
244{
245	if (!(kex->flags & KEX_INIT_SENT))
246		kex_send_kexinit(kex);
247
248	kex_choose_conf(kex);
249
250	if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
251	    kex->kex[kex->kex_type] != NULL) {
252		(kex->kex[kex->kex_type])(kex);
253	} else {
254		fatal("Unsupported key exchange %d", kex->kex_type);
255	}
256}
257
258static void
259choose_enc(Enc *enc, char *client, char *server)
260{
261	char *name = match_list(client, server, NULL);
262	if (name == NULL)
263		fatal("no matching cipher found: client %s server %s",
264		    client, server);
265	if ((enc->cipher = cipher_by_name(name)) == NULL)
266		fatal("matching cipher is not supported: %s", name);
267	enc->name = name;
268	enc->enabled = 0;
269	enc->iv = NULL;
270	enc->key = NULL;
271	enc->key_len = cipher_keylen(enc->cipher);
272	enc->block_size = cipher_blocksize(enc->cipher);
273}
274
275static void
276choose_mac(Mac *mac, char *client, char *server)
277{
278	char *name = match_list(client, server, NULL);
279	if (name == NULL)
280		fatal("no matching mac found: client %s server %s",
281		    client, server);
282	if (mac_setup(mac, name) < 0)
283		fatal("unsupported mac %s", name);
284	/* truncate the key */
285	if (datafellows & SSH_BUG_HMAC)
286		mac->key_len = 16;
287	mac->name = name;
288	mac->key = NULL;
289	mac->enabled = 0;
290}
291
292static void
293choose_comp(Comp *comp, char *client, char *server)
294{
295	char *name = match_list(client, server, NULL);
296	if (name == NULL)
297		fatal("no matching comp found: client %s server %s", client, server);
298	if (strcmp(name, "zlib@openssh.com") == 0) {
299		comp->type = COMP_DELAYED;
300	} else if (strcmp(name, "zlib") == 0) {
301		comp->type = COMP_ZLIB;
302	} else if (strcmp(name, "none") == 0) {
303		comp->type = COMP_NONE;
304	} else {
305		fatal("unsupported comp %s", name);
306	}
307	comp->name = name;
308}
309
310static void
311choose_kex(Kex *k, char *client, char *server)
312{
313	k->name = match_list(client, server, NULL);
314	if (k->name == NULL)
315		fatal("Unable to negotiate a key exchange method");
316	if (strcmp(k->name, KEX_DH1) == 0) {
317		k->kex_type = KEX_DH_GRP1_SHA1;
318		k->evp_md = EVP_sha1();
319	} else if (strcmp(k->name, KEX_DH14) == 0) {
320		k->kex_type = KEX_DH_GRP14_SHA1;
321		k->evp_md = EVP_sha1();
322	} else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
323		k->kex_type = KEX_DH_GEX_SHA1;
324		k->evp_md = EVP_sha1();
325#if OPENSSL_VERSION_NUMBER >= 0x00907000L
326	} else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
327		k->kex_type = KEX_DH_GEX_SHA256;
328		k->evp_md = evp_ssh_sha256();
329#endif
330	} else
331		fatal("bad kex alg %s", k->name);
332}
333
334static void
335choose_hostkeyalg(Kex *k, char *client, char *server)
336{
337	char *hostkeyalg = match_list(client, server, NULL);
338	if (hostkeyalg == NULL)
339		fatal("no hostkey alg");
340	k->hostkey_type = key_type_from_name(hostkeyalg);
341	if (k->hostkey_type == KEY_UNSPEC)
342		fatal("bad hostkey alg '%s'", hostkeyalg);
343	xfree(hostkeyalg);
344}
345
346static int
347proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
348{
349	static int check[] = {
350		PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
351	};
352	int *idx;
353	char *p;
354
355	for (idx = &check[0]; *idx != -1; idx++) {
356		if ((p = strchr(my[*idx], ',')) != NULL)
357			*p = '\0';
358		if ((p = strchr(peer[*idx], ',')) != NULL)
359			*p = '\0';
360		if (strcmp(my[*idx], peer[*idx]) != 0) {
361			debug2("proposal mismatch: my %s peer %s",
362			    my[*idx], peer[*idx]);
363			return (0);
364		}
365	}
366	debug2("proposals match");
367	return (1);
368}
369
370static void
371kex_choose_conf(Kex *kex)
372{
373	Newkeys *newkeys;
374	char **my, **peer;
375	char **cprop, **sprop;
376	int nenc, nmac, ncomp;
377	u_int mode, ctos, need;
378	int first_kex_follows, type;
379
380	my   = kex_buf2prop(&kex->my, NULL);
381	peer = kex_buf2prop(&kex->peer, &first_kex_follows);
382
383	if (kex->server) {
384		cprop=peer;
385		sprop=my;
386	} else {
387		cprop=my;
388		sprop=peer;
389	}
390
391	/* Algorithm Negotiation */
392	for (mode = 0; mode < MODE_MAX; mode++) {
393		newkeys = xcalloc(1, sizeof(*newkeys));
394		kex->newkeys[mode] = newkeys;
395		ctos = (!kex->server && mode == MODE_OUT) ||
396		    (kex->server && mode == MODE_IN);
397		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
398		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
399		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
400		choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
401		choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
402		choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
403		debug("kex: %s %s %s %s",
404		    ctos ? "client->server" : "server->client",
405		    newkeys->enc.name,
406		    newkeys->mac.name,
407		    newkeys->comp.name);
408	}
409	choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
410	choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
411	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
412	need = 0;
413	for (mode = 0; mode < MODE_MAX; mode++) {
414		newkeys = kex->newkeys[mode];
415		if (need < newkeys->enc.key_len)
416			need = newkeys->enc.key_len;
417		if (need < newkeys->enc.block_size)
418			need = newkeys->enc.block_size;
419		if (need < newkeys->mac.key_len)
420			need = newkeys->mac.key_len;
421	}
422	/* XXX need runden? */
423	kex->we_need = need;
424
425	/* ignore the next message if the proposals do not match */
426	if (first_kex_follows && !proposals_match(my, peer) &&
427	    !(datafellows & SSH_BUG_FIRSTKEX)) {
428		type = packet_read();
429		debug2("skipping next packet (type %u)", type);
430	}
431
432	kex_prop_free(my);
433	kex_prop_free(peer);
434}
435
436static u_char *
437derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
438    BIGNUM *shared_secret)
439{
440	Buffer b;
441	EVP_MD_CTX md;
442	char c = id;
443	u_int have;
444	int mdsz;
445	u_char *digest;
446
447	if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
448		fatal("bad kex md size %d", mdsz);
449	digest = xmalloc(roundup(need, mdsz));
450
451	buffer_init(&b);
452	buffer_put_bignum2(&b, shared_secret);
453
454	/* K1 = HASH(K || H || "A" || session_id) */
455	EVP_DigestInit(&md, kex->evp_md);
456	if (!(datafellows & SSH_BUG_DERIVEKEY))
457		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
458	EVP_DigestUpdate(&md, hash, hashlen);
459	EVP_DigestUpdate(&md, &c, 1);
460	EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
461	EVP_DigestFinal(&md, digest, NULL);
462
463	/*
464	 * expand key:
465	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
466	 * Key = K1 || K2 || ... || Kn
467	 */
468	for (have = mdsz; need > have; have += mdsz) {
469		EVP_DigestInit(&md, kex->evp_md);
470		if (!(datafellows & SSH_BUG_DERIVEKEY))
471			EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
472		EVP_DigestUpdate(&md, hash, hashlen);
473		EVP_DigestUpdate(&md, digest, have);
474		EVP_DigestFinal(&md, digest + have, NULL);
475	}
476	buffer_free(&b);
477#ifdef DEBUG_KEX
478	fprintf(stderr, "key '%c'== ", c);
479	dump_digest("key", digest, need);
480#endif
481	return digest;
482}
483
484Newkeys *current_keys[MODE_MAX];
485
486#define NKEYS	6
487void
488kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
489{
490	u_char *keys[NKEYS];
491	u_int i, mode, ctos;
492
493	for (i = 0; i < NKEYS; i++) {
494		keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
495		    shared_secret);
496	}
497
498	debug2("kex_derive_keys");
499	for (mode = 0; mode < MODE_MAX; mode++) {
500		current_keys[mode] = kex->newkeys[mode];
501		kex->newkeys[mode] = NULL;
502		ctos = (!kex->server && mode == MODE_OUT) ||
503		    (kex->server && mode == MODE_IN);
504		current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
505		current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
506		current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
507	}
508}
509
510Newkeys *
511kex_get_newkeys(int mode)
512{
513	Newkeys *ret;
514
515	ret = current_keys[mode];
516	current_keys[mode] = NULL;
517	return ret;
518}
519
520void
521derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
522    u_int8_t cookie[8], u_int8_t id[16])
523{
524	const EVP_MD *evp_md = EVP_md5();
525	EVP_MD_CTX md;
526	u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
527	int len;
528
529	EVP_DigestInit(&md, evp_md);
530
531	len = BN_num_bytes(host_modulus);
532	if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
533		fatal("%s: bad host modulus (len %d)", __func__, len);
534	BN_bn2bin(host_modulus, nbuf);
535	EVP_DigestUpdate(&md, nbuf, len);
536
537	len = BN_num_bytes(server_modulus);
538	if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
539		fatal("%s: bad server modulus (len %d)", __func__, len);
540	BN_bn2bin(server_modulus, nbuf);
541	EVP_DigestUpdate(&md, nbuf, len);
542
543	EVP_DigestUpdate(&md, cookie, 8);
544
545	EVP_DigestFinal(&md, obuf, NULL);
546	memcpy(id, obuf, 16);
547
548	memset(nbuf, 0, sizeof(nbuf));
549	memset(obuf, 0, sizeof(obuf));
550	memset(&md, 0, sizeof(md));
551}
552
553#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
554void
555dump_digest(char *msg, u_char *digest, int len)
556{
557	u_int i;
558
559	fprintf(stderr, "%s\n", msg);
560	for (i = 0; i < len; i++) {
561		fprintf(stderr, "%02x", digest[i]);
562		if (i%32 == 31)
563			fprintf(stderr, "\n");
564		else if (i%8 == 7)
565			fprintf(stderr, " ");
566	}
567	fprintf(stderr, "\n");
568}
569#endif
570