kexdhc.c revision 113908 
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: kexdhc.c,v 1.1 2003/02/16 17:09:57 markus Exp $");
27
28#include "xmalloc.h"
29#include "key.h"
30#include "kex.h"
31#include "log.h"
32#include "packet.h"
33#include "dh.h"
34#include "ssh2.h"
35
36void
37kexdh_client(Kex *kex)
38{
39	BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
40	DH *dh;
41	Key *server_host_key;
42	u_char *server_host_key_blob = NULL, *signature = NULL;
43	u_char *kbuf, *hash;
44	u_int klen, kout, slen, sbloblen;
45
46	/* generate and send 'e', client DH public key */
47	dh = dh_new_group1();
48	dh_gen_key(dh, kex->we_need * 8);
49	packet_start(SSH2_MSG_KEXDH_INIT);
50	packet_put_bignum2(dh->pub_key);
51	packet_send();
52
53	debug("sending SSH2_MSG_KEXDH_INIT");
54#ifdef DEBUG_KEXDH
55	DHparams_print_fp(stderr, dh);
56	fprintf(stderr, "pub= ");
57	BN_print_fp(stderr, dh->pub_key);
58	fprintf(stderr, "\n");
59#endif
60
61	debug("expecting SSH2_MSG_KEXDH_REPLY");
62	packet_read_expect(SSH2_MSG_KEXDH_REPLY);
63
64	/* key, cert */
65	server_host_key_blob = packet_get_string(&sbloblen);
66	server_host_key = key_from_blob(server_host_key_blob, sbloblen);
67	if (server_host_key == NULL)
68		fatal("cannot decode server_host_key_blob");
69	if (server_host_key->type != kex->hostkey_type)
70		fatal("type mismatch for decoded server_host_key_blob");
71	if (kex->verify_host_key == NULL)
72		fatal("cannot verify server_host_key");
73	if (kex->verify_host_key(server_host_key) == -1)
74		fatal("server_host_key verification failed");
75
76	/* DH paramter f, server public DH key */
77	if ((dh_server_pub = BN_new()) == NULL)
78		fatal("dh_server_pub == NULL");
79	packet_get_bignum2(dh_server_pub);
80
81#ifdef DEBUG_KEXDH
82	fprintf(stderr, "dh_server_pub= ");
83	BN_print_fp(stderr, dh_server_pub);
84	fprintf(stderr, "\n");
85	debug("bits %d", BN_num_bits(dh_server_pub));
86#endif
87
88	/* signed H */
89	signature = packet_get_string(&slen);
90	packet_check_eom();
91
92	if (!dh_pub_is_valid(dh, dh_server_pub))
93		packet_disconnect("bad server public DH value");
94
95	klen = DH_size(dh);
96	kbuf = xmalloc(klen);
97	kout = DH_compute_key(kbuf, dh_server_pub, dh);
98#ifdef DEBUG_KEXDH
99	dump_digest("shared secret", kbuf, kout);
100#endif
101	if ((shared_secret = BN_new()) == NULL)
102		fatal("kexdh_client: BN_new failed");
103	BN_bin2bn(kbuf, kout, shared_secret);
104	memset(kbuf, 0, klen);
105	xfree(kbuf);
106
107	/* calc and verify H */
108	hash = kex_dh_hash(
109	    kex->client_version_string,
110	    kex->server_version_string,
111	    buffer_ptr(&kex->my), buffer_len(&kex->my),
112	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
113	    server_host_key_blob, sbloblen,
114	    dh->pub_key,
115	    dh_server_pub,
116	    shared_secret
117	);
118	xfree(server_host_key_blob);
119	BN_clear_free(dh_server_pub);
120	DH_free(dh);
121
122	if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
123		fatal("key_verify failed for server_host_key");
124	key_free(server_host_key);
125	xfree(signature);
126
127	/* save session id */
128	if (kex->session_id == NULL) {
129		kex->session_id_len = 20;
130		kex->session_id = xmalloc(kex->session_id_len);
131		memcpy(kex->session_id, hash, kex->session_id_len);
132	}
133
134	kex_derive_keys(kex, hash, shared_secret);
135	BN_clear_free(shared_secret);
136	kex_finish(kex);
137}
138