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/opensslconf.h>
32 #include <openssl/bn.h>
33
34 #include "xmalloc.h"
35 #include "buffer.h"
36 #include "bufaux.h"
37 #include "key.h"
38 #include "kex.h"
39 #include "log.h"
40 #include "packet.h"
41 #include "dh.h"
42 #include "ssh2.h"
43 #include "compat.h"
44
45 void
46 kexgex_client(Kex *kex)
47 {
48 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
49 BIGNUM *p = NULL, *g = NULL;
50 Key *server_host_key;
51 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
52 u_int klen, kout, slen, sbloblen;
53 int min, max, nbits;
54 DH *dh;
55
56 nbits = dh_estimate(kex->we_need * 8);
57
58 if (datafellows & SSH_OLD_DHGEX) {
59 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");
60
61 /* Old GEX request */
62 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
63 packet_put_int(nbits);
64 min = DH_GRP_MIN;
65 max = DH_GRP_MAX;
66 } else {
67 debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");
68
69 /* New GEX request */
70 min = DH_GRP_MIN;
71 max = DH_GRP_MAX;
72 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
73 packet_put_int(min);
74 packet_put_int(nbits);
75 packet_put_int(max);
76 }
77 #ifdef DEBUG_KEXDH
78 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
79 min, nbits, max);
80 #endif
81 packet_send();
82
83 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
84 packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
85
86 if ((p = BN_new()) == NULL)
87 fatal("BN_new");
88 packet_get_bignum2(p);
89 if ((g = BN_new()) == NULL)
90 fatal("BN_new");
91 packet_get_bignum2(g);
92 packet_check_eom();
93
94 if (BN_num_bits(p) < min || BN_num_bits(p) > max)
95 fatal("DH_GEX group out of range: %d !< %d !< %d",
96 min, BN_num_bits(p), max);
97
98 dh = dh_new_group(g, p);
99 dh_gen_key(dh, kex->we_need * 8);
100
101 #ifdef DEBUG_KEXDH
102 DHparams_print_fp(stderr, dh);
103 fprintf(stderr, "pub= ");
104 BN_print_fp(stderr, dh->pub_key);
105 fprintf(stderr, "\n");
106 #endif
107
108 debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
109 /* generate and send 'e', client DH public key */
110 packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
111 packet_put_bignum2(dh->pub_key);
112 packet_send();
113
114 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
115 packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
116
117 /* key, cert */
118 server_host_key_blob = packet_get_string(&sbloblen);
119 server_host_key = key_from_blob(server_host_key_blob, sbloblen);
120 if (server_host_key == NULL)
121 fatal("cannot decode server_host_key_blob");
122 if (server_host_key->type != kex->hostkey_type)
123 fatal("type mismatch for decoded server_host_key_blob");
124 if (kex->verify_host_key == NULL)
125 fatal("cannot verify server_host_key");
126 if (kex->verify_host_key(server_host_key) == -1)
127 fatal("server_host_key verification failed");
128
129 /* DH paramter f, server public DH key */
130 if ((dh_server_pub = BN_new()) == NULL)
131 fatal("dh_server_pub == NULL");
132 packet_get_bignum2(dh_server_pub);
133
134 #ifdef DEBUG_KEXDH
135 fprintf(stderr, "dh_server_pub= ");
136 BN_print_fp(stderr, dh_server_pub);
137 fprintf(stderr, "\n");
138 debug("bits %d", BN_num_bits(dh_server_pub));
139 #endif
140
141 /* signed H */
142 signature = packet_get_string(&slen);
143 packet_check_eom();
144
145 if (!dh_pub_is_valid(dh, dh_server_pub))
146 packet_disconnect("bad server public DH value");
147
148 klen = DH_size(dh);
149 kbuf = xmalloc(klen);
150 kout = DH_compute_key(kbuf, dh_server_pub, dh);
151 #ifdef DEBUG_KEXDH
152 dump_digest("shared secret", kbuf, kout);
153 #endif
154 if ((shared_secret = BN_new()) == NULL)
155 fatal("kexgex_client: BN_new failed");
156 BN_bin2bn(kbuf, kout, shared_secret);
157 memset(kbuf, 0, klen);
158 xfree(kbuf);
159
160 if (datafellows & SSH_OLD_DHGEX)
161 min = max = -1;
162
163 /* calc and verify H */
164 hash = kexgex_hash(
165 kex->client_version_string,
166 kex->server_version_string,
167 buffer_ptr(&kex->my), buffer_len(&kex->my),
168 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
169 server_host_key_blob, sbloblen,
170 min, nbits, max,
171 dh->p, dh->g,
172 dh->pub_key,
173 dh_server_pub,
174 shared_secret
175 );
176 /* have keys, free DH */
177 DH_free(dh);
178 xfree(server_host_key_blob);
179 BN_clear_free(dh_server_pub);
180
181 if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
182 fatal("key_verify failed for server_host_key");
183 key_free(server_host_key);
184 xfree(signature);
185
186 /* save session id */
187 if (kex->session_id == NULL) {
188 kex->session_id_len = 20;
189 kex->session_id = xmalloc(kex->session_id_len);
190 memcpy(kex->session_id, hash, kex->session_id_len);
191 }
192 kex_derive_keys(kex, hash, shared_secret);
193 BN_clear_free(shared_secret);
194
195 kex_finish(kex);
196 }