kexdhs.c revision 262566 
1/* $OpenBSD: kexdhs.c,v 1.17 2014/01/12 08:13:13 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#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
46void
47kexdh_server(Kex *kex)
48{
49	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
50	DH *dh;
51	Key *server_host_public, *server_host_private;
52	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
53	u_int sbloblen, klen, hashlen, slen;
54	int kout;
55
56	/* generate server DH public key */
57	switch (kex->kex_type) {
58	case KEX_DH_GRP1_SHA1:
59		dh = dh_new_group1();
60		break;
61	case KEX_DH_GRP14_SHA1:
62		dh = dh_new_group14();
63		break;
64	default:
65		fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
66	}
67	dh_gen_key(dh, kex->we_need * 8);
68
69	debug("expecting SSH2_MSG_KEXDH_INIT");
70	packet_read_expect(SSH2_MSG_KEXDH_INIT);
71
72	if (kex->load_host_public_key == NULL ||
73	    kex->load_host_private_key == NULL)
74		fatal("Cannot load hostkey");
75	server_host_public = kex->load_host_public_key(kex->hostkey_type);
76	if (server_host_public == NULL)
77		fatal("Unsupported hostkey type %d", kex->hostkey_type);
78	server_host_private = kex->load_host_private_key(kex->hostkey_type);
79
80	/* key, cert */
81	if ((dh_client_pub = BN_new()) == NULL)
82		fatal("dh_client_pub == NULL");
83	packet_get_bignum2(dh_client_pub);
84	packet_check_eom();
85
86#ifdef DEBUG_KEXDH
87	fprintf(stderr, "dh_client_pub= ");
88	BN_print_fp(stderr, dh_client_pub);
89	fprintf(stderr, "\n");
90	debug("bits %d", BN_num_bits(dh_client_pub));
91#endif
92
93#ifdef DEBUG_KEXDH
94	DHparams_print_fp(stderr, dh);
95	fprintf(stderr, "pub= ");
96	BN_print_fp(stderr, dh->pub_key);
97	fprintf(stderr, "\n");
98#endif
99	if (!dh_pub_is_valid(dh, dh_client_pub))
100		packet_disconnect("bad client public DH value");
101
102	klen = DH_size(dh);
103	kbuf = xmalloc(klen);
104	if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
105		fatal("DH_compute_key: failed");
106#ifdef DEBUG_KEXDH
107	dump_digest("shared secret", kbuf, kout);
108#endif
109	if ((shared_secret = BN_new()) == NULL)
110		fatal("kexdh_server: BN_new failed");
111	if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
112		fatal("kexdh_server: BN_bin2bn failed");
113	memset(kbuf, 0, klen);
114	free(kbuf);
115
116	key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
117
118	/* calc H */
119	kex_dh_hash(
120	    kex->client_version_string,
121	    kex->server_version_string,
122	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
123	    buffer_ptr(&kex->my), buffer_len(&kex->my),
124	    server_host_key_blob, sbloblen,
125	    dh_client_pub,
126	    dh->pub_key,
127	    shared_secret,
128	    &hash, &hashlen
129	);
130	BN_clear_free(dh_client_pub);
131
132	/* save session id := H */
133	if (kex->session_id == NULL) {
134		kex->session_id_len = hashlen;
135		kex->session_id = xmalloc(kex->session_id_len);
136		memcpy(kex->session_id, hash, kex->session_id_len);
137	}
138
139	/* sign H */
140	kex->sign(server_host_private, server_host_public, &signature, &slen,
141	    hash, hashlen);
142
143	/* destroy_sensitive_data(); */
144
145	/* send server hostkey, DH pubkey 'f' and singed H */
146	packet_start(SSH2_MSG_KEXDH_REPLY);
147	packet_put_string(server_host_key_blob, sbloblen);
148	packet_put_bignum2(dh->pub_key);	/* f */
149	packet_put_string(signature, slen);
150	packet_send();
151
152	free(signature);
153	free(server_host_key_blob);
154	/* have keys, free DH */
155	DH_free(dh);
156
157	kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
158	BN_clear_free(shared_secret);
159	kex_finish(kex);
160}
161