kex.c revision 1.48 
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 1.48 2002/03/18 17:50:31 provos 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/* Use privilege separation for sshd */
48int use_privsep;
49struct monitor *monitor;
50
51
52/* prototype */
53static void kex_kexinit_finish(Kex *);
54static void kex_choose_conf(Kex *);
55
56/* put algorithm proposal into buffer */
57static void
58kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
59{
60	u_int32_t rand = 0;
61	int i;
62
63	buffer_clear(b);
64	for (i = 0; i < KEX_COOKIE_LEN; i++) {
65		if (i % 4 == 0)
66			rand = arc4random();
67		buffer_put_char(b, rand & 0xff);
68		rand >>= 8;
69	}
70	for (i = 0; i < PROPOSAL_MAX; i++)
71		buffer_put_cstring(b, proposal[i]);
72	buffer_put_char(b, 0);			/* first_kex_packet_follows */
73	buffer_put_int(b, 0);			/* uint32 reserved */
74}
75
76/* parse buffer and return algorithm proposal */
77static char **
78kex_buf2prop(Buffer *raw)
79{
80	Buffer b;
81	int i;
82	char **proposal;
83
84	proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
85
86	buffer_init(&b);
87	buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
88	/* skip cookie */
89	for (i = 0; i < KEX_COOKIE_LEN; i++)
90		buffer_get_char(&b);
91	/* extract kex init proposal strings */
92	for (i = 0; i < PROPOSAL_MAX; i++) {
93		proposal[i] = buffer_get_string(&b,NULL);
94		debug2("kex_parse_kexinit: %s", proposal[i]);
95	}
96	/* first kex follows / reserved */
97	i = buffer_get_char(&b);
98	debug2("kex_parse_kexinit: first_kex_follows %d ", i);
99	i = buffer_get_int(&b);
100	debug2("kex_parse_kexinit: reserved %d ", i);
101	buffer_free(&b);
102	return proposal;
103}
104
105static void
106kex_prop_free(char **proposal)
107{
108	int i;
109
110	for (i = 0; i < PROPOSAL_MAX; i++)
111		xfree(proposal[i]);
112	xfree(proposal);
113}
114
115static void
116kex_protocol_error(int type, u_int32_t seq, void *ctxt)
117{
118	error("Hm, kex protocol error: type %d seq %u", type, seq);
119}
120
121static void
122kex_reset_dispatch(void)
123{
124	dispatch_range(SSH2_MSG_TRANSPORT_MIN,
125	    SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
126	dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
127}
128
129void
130kex_finish(Kex *kex)
131{
132	kex_reset_dispatch();
133
134	packet_start(SSH2_MSG_NEWKEYS);
135	packet_send();
136	/* packet_write_wait(); */
137	debug("SSH2_MSG_NEWKEYS sent");
138
139	debug("waiting for SSH2_MSG_NEWKEYS");
140	packet_read_expect(SSH2_MSG_NEWKEYS);
141	packet_check_eom();
142	debug("SSH2_MSG_NEWKEYS received");
143
144	kex->done = 1;
145	buffer_clear(&kex->peer);
146	/* buffer_clear(&kex->my); */
147	kex->flags &= ~KEX_INIT_SENT;
148	xfree(kex->name);
149	kex->name = NULL;
150}
151
152void
153kex_send_kexinit(Kex *kex)
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	packet_start(SSH2_MSG_KEXINIT);
165	packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
166	packet_send();
167	debug("SSH2_MSG_KEXINIT sent");
168	kex->flags |= KEX_INIT_SENT;
169}
170
171void
172kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
173{
174	char *ptr;
175	int dlen;
176	int i;
177	Kex *kex = (Kex *)ctxt;
178
179	debug("SSH2_MSG_KEXINIT received");
180	if (kex == NULL)
181		fatal("kex_input_kexinit: no kex, cannot rekey");
182
183	ptr = packet_get_raw(&dlen);
184	buffer_append(&kex->peer, ptr, dlen);
185
186	/* discard packet */
187	for (i = 0; i < KEX_COOKIE_LEN; i++)
188		packet_get_char();
189	for (i = 0; i < PROPOSAL_MAX; i++)
190		xfree(packet_get_string(NULL));
191	packet_get_char();
192	packet_get_int();
193	packet_check_eom();
194
195	kex_kexinit_finish(kex);
196}
197
198Kex *
199kex_setup(char *proposal[PROPOSAL_MAX])
200{
201	Kex *kex;
202
203	kex = xmalloc(sizeof(*kex));
204	memset(kex, 0, sizeof(*kex));
205	buffer_init(&kex->peer);
206	buffer_init(&kex->my);
207	kex_prop2buf(&kex->my, proposal);
208	kex->done = 0;
209
210	kex_send_kexinit(kex);					/* we start */
211	kex_reset_dispatch();
212
213	return kex;
214}
215
216static void
217kex_kexinit_finish(Kex *kex)
218{
219	if (!(kex->flags & KEX_INIT_SENT))
220		kex_send_kexinit(kex);
221
222	kex_choose_conf(kex);
223
224	switch (kex->kex_type) {
225	case DH_GRP1_SHA1:
226		kexdh(kex);
227		break;
228	case DH_GEX_SHA1:
229		kexgex(kex);
230		break;
231	default:
232		fatal("Unsupported key exchange %d", kex->kex_type);
233	}
234}
235
236static void
237choose_enc(Enc *enc, char *client, char *server)
238{
239	char *name = match_list(client, server, NULL);
240	if (name == NULL)
241		fatal("no matching cipher found: client %s server %s", client, server);
242	if ((enc->cipher = cipher_by_name(name)) == NULL)
243		fatal("matching cipher is not supported: %s", name);
244	enc->name = name;
245	enc->enabled = 0;
246	enc->iv = NULL;
247	enc->key = NULL;
248	enc->key_len = cipher_keylen(enc->cipher);
249	enc->block_size = cipher_blocksize(enc->cipher);
250}
251static void
252choose_mac(Mac *mac, char *client, char *server)
253{
254	char *name = match_list(client, server, NULL);
255	if (name == NULL)
256		fatal("no matching mac found: client %s server %s", client, server);
257	if (mac_init(mac, name) < 0)
258		fatal("unsupported mac %s", name);
259	/* truncate the key */
260	if (datafellows & SSH_BUG_HMAC)
261		mac->key_len = 16;
262	mac->name = name;
263	mac->key = NULL;
264	mac->enabled = 0;
265}
266static void
267choose_comp(Comp *comp, char *client, char *server)
268{
269	char *name = match_list(client, server, NULL);
270	if (name == NULL)
271		fatal("no matching comp found: client %s server %s", client, server);
272	if (strcmp(name, "zlib") == 0) {
273		comp->type = 1;
274	} else if (strcmp(name, "none") == 0) {
275		comp->type = 0;
276	} else {
277		fatal("unsupported comp %s", name);
278	}
279	comp->name = name;
280}
281static void
282choose_kex(Kex *k, char *client, char *server)
283{
284	k->name = match_list(client, server, NULL);
285	if (k->name == NULL)
286		fatal("no kex alg");
287	if (strcmp(k->name, KEX_DH1) == 0) {
288		k->kex_type = DH_GRP1_SHA1;
289	} else if (strcmp(k->name, KEX_DHGEX) == 0) {
290		k->kex_type = DH_GEX_SHA1;
291	} else
292		fatal("bad kex alg %s", k->name);
293}
294static void
295choose_hostkeyalg(Kex *k, char *client, char *server)
296{
297	char *hostkeyalg = match_list(client, server, NULL);
298	if (hostkeyalg == NULL)
299		fatal("no hostkey alg");
300	k->hostkey_type = key_type_from_name(hostkeyalg);
301	if (k->hostkey_type == KEY_UNSPEC)
302		fatal("bad hostkey alg '%s'", hostkeyalg);
303	xfree(hostkeyalg);
304}
305
306static void
307kex_choose_conf(Kex *kex)
308{
309	Newkeys *newkeys;
310	char **my, **peer;
311	char **cprop, **sprop;
312	int nenc, nmac, ncomp;
313	int mode;
314	int ctos;				/* direction: if true client-to-server */
315	int need;
316
317	my   = kex_buf2prop(&kex->my);
318	peer = kex_buf2prop(&kex->peer);
319
320	if (kex->server) {
321		cprop=peer;
322		sprop=my;
323	} else {
324		cprop=my;
325		sprop=peer;
326	}
327
328	/* Algorithm Negotiation */
329	for (mode = 0; mode < MODE_MAX; mode++) {
330		newkeys = xmalloc(sizeof(*newkeys));
331		memset(newkeys, 0, sizeof(*newkeys));
332		kex->newkeys[mode] = newkeys;
333		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
334		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
335		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
336		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
337		choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
338		choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
339		choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
340		debug("kex: %s %s %s %s",
341		    ctos ? "client->server" : "server->client",
342		    newkeys->enc.name,
343		    newkeys->mac.name,
344		    newkeys->comp.name);
345	}
346	choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
347	choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
348	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
349	need = 0;
350	for (mode = 0; mode < MODE_MAX; mode++) {
351		newkeys = kex->newkeys[mode];
352		if (need < newkeys->enc.key_len)
353			need = newkeys->enc.key_len;
354		if (need < newkeys->enc.block_size)
355			need = newkeys->enc.block_size;
356		if (need < newkeys->mac.key_len)
357			need = newkeys->mac.key_len;
358	}
359	/* XXX need runden? */
360	kex->we_need = need;
361
362	kex_prop_free(my);
363	kex_prop_free(peer);
364}
365
366static u_char *
367derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
368{
369	Buffer b;
370	const EVP_MD *evp_md = EVP_sha1();
371	EVP_MD_CTX md;
372	char c = id;
373	int have;
374	int mdsz = EVP_MD_size(evp_md);
375	u_char *digest = xmalloc(roundup(need, mdsz));
376
377	buffer_init(&b);
378	buffer_put_bignum2(&b, shared_secret);
379
380	/* K1 = HASH(K || H || "A" || session_id) */
381	EVP_DigestInit(&md, evp_md);
382	if (!(datafellows & SSH_BUG_DERIVEKEY))
383		EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
384	EVP_DigestUpdate(&md, hash, mdsz);
385	EVP_DigestUpdate(&md, &c, 1);
386	EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
387	EVP_DigestFinal(&md, digest, NULL);
388
389	/*
390	 * expand key:
391	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
392	 * Key = K1 || K2 || ... || Kn
393	 */
394	for (have = mdsz; need > have; have += mdsz) {
395		EVP_DigestInit(&md, evp_md);
396		if (!(datafellows & SSH_BUG_DERIVEKEY))
397			EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
398		EVP_DigestUpdate(&md, hash, mdsz);
399		EVP_DigestUpdate(&md, digest, have);
400		EVP_DigestFinal(&md, digest + have, NULL);
401	}
402	buffer_free(&b);
403#ifdef DEBUG_KEX
404	fprintf(stderr, "key '%c'== ", c);
405	dump_digest("key", digest, need);
406#endif
407	return digest;
408}
409
410Newkeys *current_keys[MODE_MAX];
411
412#define NKEYS	6
413void
414kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
415{
416	u_char *keys[NKEYS];
417	int i, mode, ctos;
418
419	for (i = 0; i < NKEYS; i++)
420		keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
421
422	debug("kex_derive_keys");
423	for (mode = 0; mode < MODE_MAX; mode++) {
424		current_keys[mode] = kex->newkeys[mode];
425		kex->newkeys[mode] = NULL;
426		ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
427		current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
428		current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
429		current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
430	}
431}
432
433Newkeys *
434kex_get_newkeys(int mode)
435{
436	Newkeys *ret;
437
438	ret = current_keys[mode];
439	current_keys[mode] = NULL;
440	return ret;
441}
442
443#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
444void
445dump_digest(char *msg, u_char *digest, int len)
446{
447	int i;
448
449	fprintf(stderr, "%s\n", msg);
450	for (i = 0; i< len; i++) {
451		fprintf(stderr, "%02x", digest[i]);
452		if (i%32 == 31)
453			fprintf(stderr, "\n");
454		else if (i%8 == 7)
455			fprintf(stderr, " ");
456	}
457	fprintf(stderr, "\n");
458}
459#endif
460