1 /*
2 * Copyright (c) 2000 Niels Provos. All rights reserved.
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 RCSID("$OpenBSD: kexgex.c,v 1.22 2002/03/24 17:27:03 stevesk Exp $");
28
29 #pragma ident "%Z%%M% %I% %E% SMI"
30
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 #include "compat.h"
43
44 void
45 kexgex_client(Kex *kex)
46 {
47 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
48 BIGNUM *p = NULL, *g = NULL;
49 Key *server_host_key;
50 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
51 u_int klen, kout, slen, sbloblen;
52 int min, max, nbits;
53 DH *dh;
54
55 nbits = dh_estimate(kex->we_need * 8);
56
57 if (datafellows & SSH_OLD_DHGEX) {
58 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");
59
60 /* Old GEX request */
61 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
62 packet_put_int(nbits);
63 min = DH_GRP_MIN;
64 max = DH_GRP_MAX;
65 } else {
66 debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");
67
68 /* New GEX request */
69 min = DH_GRP_MIN;
70 max = DH_GRP_MAX;
71 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
72 packet_put_int(min);
73 packet_put_int(nbits);
74 packet_put_int(max);
75 }
76 #ifdef DEBUG_KEXDH
77 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
78 min, nbits, max);
79 #endif
80 packet_send();
81
82 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
83 packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
84
85 if ((p = BN_new()) == NULL)
86 fatal("BN_new");
87 packet_get_bignum2(p);
88 if ((g = BN_new()) == NULL)
89 fatal("BN_new");
90 packet_get_bignum2(g);
91 packet_check_eom();
92
93 if (BN_num_bits(p) < min || BN_num_bits(p) > max)
94 fatal("DH_GEX group out of range: %d !< %d !< %d",
95 min, BN_num_bits(p), max);
96
97 dh = dh_new_group(g, p);
98 dh_gen_key(dh, kex->we_need * 8);
99
100 #ifdef DEBUG_KEXDH
101 DHparams_print_fp(stderr, dh);
102 fprintf(stderr, "pub= ");
103 BN_print_fp(stderr, dh->pub_key);
104 fprintf(stderr, "\n");
105 #endif
106
107 debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
108 /* generate and send 'e', client DH public key */
109 packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
110 packet_put_bignum2(dh->pub_key);
111 packet_send();
112
113 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
114 packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
115
116 /* key, cert */
117 server_host_key_blob = packet_get_string(&sbloblen);
118 server_host_key = key_from_blob(server_host_key_blob, sbloblen);
119 if (server_host_key == NULL)
120 fatal("cannot decode server_host_key_blob");
121 if (server_host_key->type != kex->hostkey_type)
122 fatal("type mismatch for decoded server_host_key_blob");
123 if (kex->verify_host_key == NULL)
124 fatal("cannot verify server_host_key");
125 if (kex->verify_host_key(server_host_key) == -1)
126 fatal("server_host_key verification failed");
127
128 /* DH paramter f, server public DH key */
129 if ((dh_server_pub = BN_new()) == NULL)
130 fatal("dh_server_pub == NULL");
131 packet_get_bignum2(dh_server_pub);
132
133 #ifdef DEBUG_KEXDH
134 fprintf(stderr, "dh_server_pub= ");
135 BN_print_fp(stderr, dh_server_pub);
136 fprintf(stderr, "\n");
137 debug("bits %d", BN_num_bits(dh_server_pub));
138 #endif
139
140 /* signed H */
141 signature = packet_get_string(&slen);
142 packet_check_eom();
143
144 if (!dh_pub_is_valid(dh, dh_server_pub))
145 packet_disconnect("bad server public DH value");
146
147 klen = DH_size(dh);
148 kbuf = xmalloc(klen);
149 kout = DH_compute_key(kbuf, dh_server_pub, dh);
150 #ifdef DEBUG_KEXDH
151 dump_digest("shared secret", kbuf, kout);
152 #endif
153 if ((shared_secret = BN_new()) == NULL)
154 fatal("kexgex_client: BN_new failed");
155 BN_bin2bn(kbuf, kout, shared_secret);
156 memset(kbuf, 0, klen);
157 xfree(kbuf);
158
159 if (datafellows & SSH_OLD_DHGEX)
160 min = max = -1;
161
162 /* calc and verify H */
163 hash = kexgex_hash(
164 kex->client_version_string,
165 kex->server_version_string,
166 buffer_ptr(&kex->my), buffer_len(&kex->my),
167 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
168 server_host_key_blob, sbloblen,
169 min, nbits, max,
170 dh->p, dh->g,
171 dh->pub_key,
172 dh_server_pub,
173 shared_secret
174 );
175 /* have keys, free DH */
176 DH_free(dh);
177 xfree(server_host_key_blob);
178 BN_clear_free(dh_server_pub);
179
180 if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
181 fatal("key_verify failed for server_host_key");
182 key_free(server_host_key);
183 xfree(signature);
184
185 /* save session id */
186 if (kex->session_id == NULL) {
187 kex->session_id_len = 20;
188 kex->session_id = xmalloc(kex->session_id_len);
189 memcpy(kex->session_id, hash, kex->session_id_len);
190 }
191 kex_derive_keys(kex, hash, shared_secret);
192 BN_clear_free(shared_secret);
193
194 kex_finish(kex);
195 }