1/*
2 * Copyright (c) 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: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $");
27
28#pragma ident	"%Z%%M%	%I%	%E% SMI"
29
30#include <openssl/crypto.h>
31#include <openssl/bn.h>
32
33#include "xmalloc.h"
34#include "buffer.h"
35#include "bufaux.h"
36#include "key.h"
37#include "kex.h"
38#include "log.h"
39#include "packet.h"
40#include "dh.h"
41#include "ssh2.h"
42
43void
44kexdh_client(Kex *kex)
45{
46	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
47	DH *dh;
48	Key *server_host_key;
49	u_char *server_host_key_blob = NULL, *signature = NULL;
50	u_char *kbuf, *hash;
51	u_int klen, kout, slen, sbloblen;
52
53	/* generate and send 'e', client DH public key */
54	dh = dh_new_group1();
55	dh_gen_key(dh, kex->we_need * 8);
56	packet_start(SSH2_MSG_KEXDH_INIT);
57	packet_put_bignum2(dh->pub_key);
58	packet_send();
59
60	debug("sending SSH2_MSG_KEXDH_INIT");
61#ifdef DEBUG_KEXDH
62	DHparams_print_fp(stderr, dh);
63	fprintf(stderr, "pub= ");
64	BN_print_fp(stderr, dh->pub_key);
65	fprintf(stderr, "\n");
66#endif
67
68	debug("expecting SSH2_MSG_KEXDH_REPLY");
69	packet_read_expect(SSH2_MSG_KEXDH_REPLY);
70
71	/* key, cert */
72	server_host_key_blob = packet_get_string(&sbloblen);
73	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
74	if (server_host_key == NULL)
75		fatal("cannot decode server_host_key_blob");
76	if (server_host_key->type != kex->hostkey_type)
77		fatal("type mismatch for decoded server_host_key_blob");
78	if (kex->verify_host_key == NULL)
79		fatal("cannot verify server_host_key");
80	if (kex->verify_host_key(server_host_key) == -1)
81		fatal("server_host_key verification failed");
82
83	/* DH paramter f, server public DH key */
84	if ((dh_server_pub = BN_new()) == NULL)
85		fatal("dh_server_pub == NULL");
86	packet_get_bignum2(dh_server_pub);
87
88#ifdef DEBUG_KEXDH
89	fprintf(stderr, "dh_server_pub= ");
90	BN_print_fp(stderr, dh_server_pub);
91	fprintf(stderr, "\n");
92	debug("bits %d", BN_num_bits(dh_server_pub));
93#endif
94
95	/* signed H */
96	signature = packet_get_string(&slen);
97	packet_check_eom();
98
99	if (!dh_pub_is_valid(dh, dh_server_pub))
100		packet_disconnect("bad server public DH value");
101
102	klen = DH_size(dh);
103	kbuf = xmalloc(klen);
104	kout = DH_compute_key(kbuf, dh_server_pub, dh);
105#ifdef DEBUG_KEXDH
106	dump_digest("shared secret", kbuf, kout);
107#endif
108	if ((shared_secret = BN_new()) == NULL)
109		fatal("kexdh_client: BN_new failed");
110	BN_bin2bn(kbuf, kout, shared_secret);
111	memset(kbuf, 0, klen);
112	xfree(kbuf);
113
114	/* calc and verify H */
115	hash = kex_dh_hash(
116	    kex->client_version_string,
117	    kex->server_version_string,
118	    buffer_ptr(&kex->my), buffer_len(&kex->my),
119	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
120	    server_host_key_blob, sbloblen,
121	    dh->pub_key,
122	    dh_server_pub,
123	    shared_secret
124	);
125	xfree(server_host_key_blob);
126	BN_clear_free(dh_server_pub);
127	DH_free(dh);
128
129	if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
130		fatal("key_verify failed for server_host_key");
131	key_free(server_host_key);
132	xfree(signature);
133
134	/* save session id */
135	if (kex->session_id == NULL) {
136		kex->session_id_len = 20;
137		kex->session_id = xmalloc(kex->session_id_len);
138		memcpy(kex->session_id, hash, kex->session_id_len);
139	}
140
141	kex_derive_keys(kex, hash, shared_secret);
142	BN_clear_free(shared_secret);
143	kex_finish(kex);
144}
145