1/* $OpenBSD: kexdhc.c,v 1.12 2010/11/10 01:33:07 djm Exp $ */
2/*
3 * Copyright (c) 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/types.h>
29
30#ifdef __APPLE_CRYPTO__
31#include "ossl-dh.h"
32#else
33#include <openssl/dh.h>
34#endif
35
36#include <stdarg.h>
37#include <stdio.h>
38#include <string.h>
39#include <signal.h>
40
41#include "xmalloc.h"
42#include "buffer.h"
43#include "key.h"
44#include "cipher.h"
45#include "kex.h"
46#include "log.h"
47#include "packet.h"
48#include "dh.h"
49#include "ssh2.h"
50
51void
52kexdh_client(Kex *kex)
53{
54	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
55	DH *dh;
56	Key *server_host_key;
57	u_char *server_host_key_blob = NULL, *signature = NULL;
58	u_char *kbuf, *hash;
59	u_int klen, slen, sbloblen, hashlen;
60	int kout;
61
62	/* generate and send 'e', client DH public key */
63	switch (kex->kex_type) {
64	case KEX_DH_GRP1_SHA1:
65		dh = dh_new_group1();
66		break;
67	case KEX_DH_GRP14_SHA1:
68		dh = dh_new_group14();
69		break;
70	default:
71		fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
72	}
73	dh_gen_key(dh, kex->we_need * 8);
74	packet_start(SSH2_MSG_KEXDH_INIT);
75	packet_put_bignum2(dh->pub_key);
76	packet_send();
77
78	debug("sending SSH2_MSG_KEXDH_INIT");
79#ifdef DEBUG_KEXDH
80	DHparams_print_fp(stderr, dh);
81	fprintf(stderr, "pub= ");
82	BN_print_fp(stderr, dh->pub_key);
83	fprintf(stderr, "\n");
84#endif
85
86	debug("expecting SSH2_MSG_KEXDH_REPLY");
87	packet_read_expect(SSH2_MSG_KEXDH_REPLY);
88
89	/* key, cert */
90	server_host_key_blob = packet_get_string(&sbloblen);
91	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
92	if (server_host_key == NULL)
93		fatal("cannot decode server_host_key_blob");
94	if (server_host_key->type != kex->hostkey_type)
95		fatal("type mismatch for decoded server_host_key_blob");
96	if (kex->verify_host_key == NULL)
97		fatal("cannot verify server_host_key");
98	if (kex->verify_host_key(server_host_key) == -1)
99		fatal("server_host_key verification failed");
100
101	/* DH parameter f, server public DH key */
102	if ((dh_server_pub = BN_new()) == NULL)
103		fatal("dh_server_pub == NULL");
104	packet_get_bignum2(dh_server_pub);
105
106#ifdef DEBUG_KEXDH
107	fprintf(stderr, "dh_server_pub= ");
108	BN_print_fp(stderr, dh_server_pub);
109	fprintf(stderr, "\n");
110	debug("bits %d", BN_num_bits(dh_server_pub));
111#endif
112
113	/* signed H */
114	signature = packet_get_string(&slen);
115	packet_check_eom();
116
117	if (!dh_pub_is_valid(dh, dh_server_pub))
118		packet_disconnect("bad server public DH value");
119
120	klen = DH_size(dh);
121	kbuf = xmalloc(klen);
122	if ((kout = DH_compute_key(kbuf, dh_server_pub, dh)) < 0)
123		fatal("DH_compute_key: failed");
124#ifdef DEBUG_KEXDH
125	dump_digest("shared secret", kbuf, kout);
126#endif
127	if ((shared_secret = BN_new()) == NULL)
128		fatal("kexdh_client: BN_new failed");
129	if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
130		fatal("kexdh_client: BN_bin2bn failed");
131	memset(kbuf, 0, klen);
132	xfree(kbuf);
133
134	/* calc and verify H */
135	kex_dh_hash(
136	    kex->client_version_string,
137	    kex->server_version_string,
138	    buffer_ptr(&kex->my), buffer_len(&kex->my),
139	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
140	    server_host_key_blob, sbloblen,
141	    dh->pub_key,
142	    dh_server_pub,
143	    shared_secret,
144	    &hash, &hashlen
145	);
146	xfree(server_host_key_blob);
147	BN_clear_free(dh_server_pub);
148	DH_free(dh);
149
150	if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
151		fatal("key_verify failed for server_host_key");
152	key_free(server_host_key);
153	xfree(signature);
154
155	/* save session id */
156	if (kex->session_id == NULL) {
157		kex->session_id_len = hashlen;
158		kex->session_id = xmalloc(kex->session_id_len);
159		memcpy(kex->session_id, hash, kex->session_id_len);
160	}
161
162	kex_derive_keys(kex, hash, hashlen, shared_secret);
163	BN_clear_free(shared_secret);
164	kex_finish(kex);
165}
166