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_server(Kex *kex)
46 {
47 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
48 Key *server_host_key;
49 DH *dh;
50 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
51 u_int sbloblen, klen, kout, slen;
52 int min = -1, max = -1, nbits = -1, type;
53
54 if (kex->load_host_key == NULL)
55 fatal("Cannot load hostkey");
56 server_host_key = kex->load_host_key(kex->hostkey_type);
57 if (server_host_key == NULL)
58 fatal("Unsupported hostkey type %d", kex->hostkey_type);
59
60 type = packet_read();
61 switch (type) {
62 case SSH2_MSG_KEX_DH_GEX_REQUEST:
63 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
64 min = packet_get_int();
65 nbits = packet_get_int();
66 max = packet_get_int();
67 min = MAX(DH_GRP_MIN, min);
68 max = MIN(DH_GRP_MAX, max);
69 break;
70 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
71 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
72 nbits = packet_get_int();
73 min = DH_GRP_MIN;
74 max = DH_GRP_MAX;
75 /* unused for old GEX */
76 break;
77 default:
78 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
79 }
80 packet_check_eom();
81
82 if (max < min || nbits < min || max < nbits)
83 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
84 min, nbits, max);
85
86 /* Contact privileged parent */
87 dh = choose_dh(min, nbits, max);
88 if (dh == NULL)
89 packet_disconnect("Protocol error: no matching DH grp found");
90
91 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
92 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
93 packet_put_bignum2(dh->p);
94 packet_put_bignum2(dh->g);
95 packet_send();
96
97 /* flush */
98 packet_write_wait();
99
100 /* Compute our exchange value in parallel with the client */
101 dh_gen_key(dh, kex->we_need * 8);
102
103 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
104 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
105
106 /* key, cert */
107 if ((dh_client_pub = BN_new()) == NULL)
108 fatal("dh_client_pub == NULL");
109 packet_get_bignum2(dh_client_pub);
110 packet_check_eom();
111
112 #ifdef DEBUG_KEXDH
113 fprintf(stderr, "dh_client_pub= ");
114 BN_print_fp(stderr, dh_client_pub);
115 fprintf(stderr, "\n");
116 debug("bits %d", BN_num_bits(dh_client_pub));
117 #endif
118
119 #ifdef DEBUG_KEXDH
120 DHparams_print_fp(stderr, dh);
121 fprintf(stderr, "pub= ");
122 BN_print_fp(stderr, dh->pub_key);
123 fprintf(stderr, "\n");
124 #endif
125 if (!dh_pub_is_valid(dh, dh_client_pub))
126 packet_disconnect("bad client public DH value");
127
128 klen = DH_size(dh);
129 kbuf = xmalloc(klen);
130 kout = DH_compute_key(kbuf, dh_client_pub, dh);
131 #ifdef DEBUG_KEXDH
132 dump_digest("shared secret", kbuf, kout);
133 #endif
134 if ((shared_secret = BN_new()) == NULL)
135 fatal("kexgex_server: BN_new failed");
136 BN_bin2bn(kbuf, kout, shared_secret);
137 memset(kbuf, 0, klen);
138 xfree(kbuf);
139
140 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
141
142 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
143 min = max = -1;
144
145 /* calc H */ /* XXX depends on 'kex' */
146 hash = kexgex_hash(
147 kex->client_version_string,
148 kex->server_version_string,
149 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
150 buffer_ptr(&kex->my), buffer_len(&kex->my),
151 server_host_key_blob, sbloblen,
152 min, nbits, max,
153 dh->p, dh->g,
154 dh_client_pub,
155 dh->pub_key,
156 shared_secret
157 );
158 BN_clear_free(dh_client_pub);
159
160 /* save session id := H */
161 /* XXX hashlen depends on KEX */
162 if (kex->session_id == NULL) {
163 kex->session_id_len = 20;
164 kex->session_id = xmalloc(kex->session_id_len);
165 memcpy(kex->session_id, hash, kex->session_id_len);
166 }
167
168 /* sign H */
169 /* XXX hashlen depends on KEX */
170 key_sign(server_host_key, &signature, &slen, hash, 20);
171
172 /* destroy_sensitive_data(); */
173
174 /* send server hostkey, DH pubkey 'f' and singed H */
175 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
176 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
177 packet_put_string(server_host_key_blob, sbloblen);
178 packet_put_bignum2(dh->pub_key); /* f */
179 packet_put_string(signature, slen);
180 packet_send();
181
182 xfree(signature);
183 xfree(server_host_key_blob);
184 /* have keys, free DH */
185 DH_free(dh);
186
187 kex_derive_keys(kex, hash, shared_secret);
188 BN_clear_free(shared_secret);
189
190 kex_finish(kex);
191 }