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Damien Miller8e7fb332003-02-24 12:03:03 +11001/*
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"
Damien Miller19bb3a52005-11-05 15:19:35 +110027RCSID("$OpenBSD: kexgexs.c,v 1.2 2005/11/04 05:15:59 djm Exp $");
Damien Miller8e7fb332003-02-24 12:03:03 +110028
29#include "xmalloc.h"
30#include "key.h"
31#include "kex.h"
32#include "log.h"
33#include "packet.h"
34#include "dh.h"
35#include "ssh2.h"
36#include "compat.h"
37#include "monitor_wrap.h"
38
39void
40kexgex_server(Kex *kex)
41{
42 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
43 Key *server_host_key;
44 DH *dh;
45 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
Damien Miller19bb3a52005-11-05 15:19:35 +110046 u_int sbloblen, klen, kout, slen, hashlen;
Damien Miller8e7fb332003-02-24 12:03:03 +110047 int min = -1, max = -1, nbits = -1, type;
48
49 if (kex->load_host_key == NULL)
50 fatal("Cannot load hostkey");
51 server_host_key = kex->load_host_key(kex->hostkey_type);
52 if (server_host_key == NULL)
53 fatal("Unsupported hostkey type %d", kex->hostkey_type);
54
55 type = packet_read();
56 switch (type) {
57 case SSH2_MSG_KEX_DH_GEX_REQUEST:
58 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
59 min = packet_get_int();
60 nbits = packet_get_int();
61 max = packet_get_int();
62 min = MAX(DH_GRP_MIN, min);
63 max = MIN(DH_GRP_MAX, max);
64 break;
65 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
66 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
67 nbits = packet_get_int();
68 min = DH_GRP_MIN;
69 max = DH_GRP_MAX;
70 /* unused for old GEX */
71 break;
72 default:
73 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
74 }
75 packet_check_eom();
76
77 if (max < min || nbits < min || max < nbits)
78 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
79 min, nbits, max);
80
81 /* Contact privileged parent */
82 dh = PRIVSEP(choose_dh(min, nbits, max));
83 if (dh == NULL)
84 packet_disconnect("Protocol error: no matching DH grp found");
85
86 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
87 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
88 packet_put_bignum2(dh->p);
89 packet_put_bignum2(dh->g);
90 packet_send();
91
92 /* flush */
93 packet_write_wait();
94
95 /* Compute our exchange value in parallel with the client */
96 dh_gen_key(dh, kex->we_need * 8);
97
98 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
99 packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
100
101 /* key, cert */
102 if ((dh_client_pub = BN_new()) == NULL)
103 fatal("dh_client_pub == NULL");
104 packet_get_bignum2(dh_client_pub);
105 packet_check_eom();
106
107#ifdef DEBUG_KEXDH
108 fprintf(stderr, "dh_client_pub= ");
109 BN_print_fp(stderr, dh_client_pub);
110 fprintf(stderr, "\n");
111 debug("bits %d", BN_num_bits(dh_client_pub));
112#endif
113
114#ifdef DEBUG_KEXDH
115 DHparams_print_fp(stderr, dh);
116 fprintf(stderr, "pub= ");
117 BN_print_fp(stderr, dh->pub_key);
118 fprintf(stderr, "\n");
119#endif
120 if (!dh_pub_is_valid(dh, dh_client_pub))
121 packet_disconnect("bad client public DH value");
122
123 klen = DH_size(dh);
124 kbuf = xmalloc(klen);
125 kout = DH_compute_key(kbuf, dh_client_pub, dh);
126#ifdef DEBUG_KEXDH
127 dump_digest("shared secret", kbuf, kout);
128#endif
129 if ((shared_secret = BN_new()) == NULL)
130 fatal("kexgex_server: BN_new failed");
131 BN_bin2bn(kbuf, kout, shared_secret);
132 memset(kbuf, 0, klen);
133 xfree(kbuf);
134
135 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
136
137 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
138 min = max = -1;
139
Damien Miller19bb3a52005-11-05 15:19:35 +1100140 /* calc H */
141 kexgex_hash(
142 kex->evp_md,
Damien Miller8e7fb332003-02-24 12:03:03 +1100143 kex->client_version_string,
144 kex->server_version_string,
145 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
146 buffer_ptr(&kex->my), buffer_len(&kex->my),
147 server_host_key_blob, sbloblen,
148 min, nbits, max,
149 dh->p, dh->g,
150 dh_client_pub,
151 dh->pub_key,
Damien Miller19bb3a52005-11-05 15:19:35 +1100152 shared_secret,
153 &hash, &hashlen
Damien Miller8e7fb332003-02-24 12:03:03 +1100154 );
155 BN_clear_free(dh_client_pub);
156
157 /* save session id := H */
Damien Miller8e7fb332003-02-24 12:03:03 +1100158 if (kex->session_id == NULL) {
Damien Miller19bb3a52005-11-05 15:19:35 +1100159 kex->session_id_len = hashlen;
Damien Miller8e7fb332003-02-24 12:03:03 +1100160 kex->session_id = xmalloc(kex->session_id_len);
161 memcpy(kex->session_id, hash, kex->session_id_len);
162 }
163
164 /* sign H */
Damien Miller19bb3a52005-11-05 15:19:35 +1100165 PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
Damien Miller8e7fb332003-02-24 12:03:03 +1100166
167 /* destroy_sensitive_data(); */
168
169 /* send server hostkey, DH pubkey 'f' and singed H */
170 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
171 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
172 packet_put_string(server_host_key_blob, sbloblen);
173 packet_put_bignum2(dh->pub_key); /* f */
174 packet_put_string(signature, slen);
175 packet_send();
176
177 xfree(signature);
178 xfree(server_host_key_blob);
179 /* have keys, free DH */
180 DH_free(dh);
181
Damien Miller19bb3a52005-11-05 15:19:35 +1100182 kex_derive_keys(kex, hash, hashlen, shared_secret);
Damien Miller8e7fb332003-02-24 12:03:03 +1100183 BN_clear_free(shared_secret);
184
185 kex_finish(kex);
186}