1/* $OpenBSD: kexdhs.c,v 1.14 2013/07/19 07:37:48 markus 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#include <stdarg.h>
31#include <string.h>
32#include <signal.h>
33
34#include <openssl/dh.h>
35
36#include "xmalloc.h"
37#include "buffer.h"
38#include "key.h"
39#include "cipher.h"
40#include "kex.h"
41#include "log.h"
42#include "packet.h"
43#include "dh.h"
44#include "ssh2.h"
45#ifdef GSSAPI
46#include "ssh-gss.h"
47#endif
48#include "monitor_wrap.h"
49
50void
51kexdh_server(Kex *kex)
52{
53	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
54	DH *dh;
55	Key *server_host_public, *server_host_private;
56	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
57	u_int sbloblen, klen, hashlen, slen;
58	int kout;
59
60	/* generate server DH public key */
61	switch (kex->kex_type) {
62	case KEX_DH_GRP1_SHA1:
63		dh = dh_new_group1();
64		break;
65	case KEX_DH_GRP14_SHA1:
66		dh = dh_new_group14();
67		break;
68	default:
69		fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
70	}
71	dh_gen_key(dh, kex->we_need * 8);
72
73	debug("expecting SSH2_MSG_KEXDH_INIT");
74	packet_read_expect(SSH2_MSG_KEXDH_INIT);
75
76	if (kex->load_host_public_key == NULL ||
77	    kex->load_host_private_key == NULL)
78		fatal("Cannot load hostkey");
79	server_host_public = kex->load_host_public_key(kex->hostkey_type);
80	if (server_host_public == NULL)
81		fatal("Unsupported hostkey type %d", kex->hostkey_type);
82	server_host_private = kex->load_host_private_key(kex->hostkey_type);
83
84	/* key, cert */
85	if ((dh_client_pub = BN_new()) == NULL)
86		fatal("dh_client_pub == NULL");
87	packet_get_bignum2(dh_client_pub);
88	packet_check_eom();
89
90#ifdef DEBUG_KEXDH
91	fprintf(stderr, "dh_client_pub= ");
92	BN_print_fp(stderr, dh_client_pub);
93	fprintf(stderr, "\n");
94	debug("bits %d", BN_num_bits(dh_client_pub));
95#endif
96
97#ifdef DEBUG_KEXDH
98	DHparams_print_fp(stderr, dh);
99	fprintf(stderr, "pub= ");
100	BN_print_fp(stderr, dh->pub_key);
101	fprintf(stderr, "\n");
102#endif
103	if (!dh_pub_is_valid(dh, dh_client_pub))
104		packet_disconnect("bad client public DH value");
105
106	klen = DH_size(dh);
107	kbuf = xmalloc(klen);
108	if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
109		fatal("DH_compute_key: failed");
110#ifdef DEBUG_KEXDH
111	dump_digest("shared secret", kbuf, kout);
112#endif
113	if ((shared_secret = BN_new()) == NULL)
114		fatal("kexdh_server: BN_new failed");
115	if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
116		fatal("kexdh_server: BN_bin2bn failed");
117	memset(kbuf, 0, klen);
118	free(kbuf);
119
120	key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
121
122	/* calc H */
123	kex_dh_hash(
124	    kex->client_version_string,
125	    kex->server_version_string,
126	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
127	    buffer_ptr(&kex->my), buffer_len(&kex->my),
128	    server_host_key_blob, sbloblen,
129	    dh_client_pub,
130	    dh->pub_key,
131	    shared_secret,
132	    &hash, &hashlen
133	);
134	BN_clear_free(dh_client_pub);
135
136	/* save session id := H */
137	if (kex->session_id == NULL) {
138		kex->session_id_len = hashlen;
139		kex->session_id = xmalloc(kex->session_id_len);
140		memcpy(kex->session_id, hash, kex->session_id_len);
141	}
142
143	/* sign H */
144	kex->sign(server_host_private, server_host_public, &signature, &slen,
145	    hash, hashlen);
146
147	/* destroy_sensitive_data(); */
148
149	/* send server hostkey, DH pubkey 'f' and singed H */
150	packet_start(SSH2_MSG_KEXDH_REPLY);
151	packet_put_string(server_host_key_blob, sbloblen);
152	packet_put_bignum2(dh->pub_key);	/* f */
153	packet_put_string(signature, slen);
154	packet_send();
155
156	free(signature);
157	free(server_host_key_blob);
158	/* have keys, free DH */
159	DH_free(dh);
160
161	kex_derive_keys(kex, hash, hashlen, shared_secret);
162	BN_clear_free(shared_secret);
163	kex_finish(kex);
164}
165