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Damien Millerd7834352006-08-05 12:39:39 +10001/* $OpenBSD: kexgexc.c,v 1.9 2006/08/03 03:34:42 deraadt Exp $ */
Damien Miller8e7fb332003-02-24 12:03:03 +11002/*
3 * Copyright (c) 2000 Niels Provos. All rights reserved.
4 * Copyright (c) 2001 Markus Friedl. All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include "includes.h"
Damien Miller8e7fb332003-02-24 12:03:03 +110028
Damien Millerd7834352006-08-05 12:39:39 +100029#include <sys/types.h>
30
Damien Millera7a73ee2006-08-05 11:37:59 +100031#include <stdio.h>
Damien Millere3476ed2006-07-24 14:13:33 +100032#include <string.h>
Damien Millerd7834352006-08-05 12:39:39 +100033#include <signal.h>
Damien Millere3476ed2006-07-24 14:13:33 +100034
Damien Miller8e7fb332003-02-24 12:03:03 +110035#include "xmalloc.h"
Damien Millerd7834352006-08-05 12:39:39 +100036#include "buffer.h"
Damien Miller8e7fb332003-02-24 12:03:03 +110037#include "key.h"
Damien Millerd7834352006-08-05 12:39:39 +100038#include "cipher.h"
Damien Miller8e7fb332003-02-24 12:03:03 +110039#include "kex.h"
40#include "log.h"
41#include "packet.h"
42#include "dh.h"
43#include "ssh2.h"
44#include "compat.h"
45
46void
47kexgex_client(Kex *kex)
48{
49 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
50 BIGNUM *p = NULL, *g = NULL;
51 Key *server_host_key;
52 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
Damien Miller19bb3a52005-11-05 15:19:35 +110053 u_int klen, kout, slen, sbloblen, hashlen;
Damien Miller8e7fb332003-02-24 12:03:03 +110054 int min, max, nbits;
55 DH *dh;
56
57 nbits = dh_estimate(kex->we_need * 8);
58
59 if (datafellows & SSH_OLD_DHGEX) {
Damien Miller8e7fb332003-02-24 12:03:03 +110060 /* 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;
Damien Miller8e7fb332003-02-24 12:03:03 +110065
Darren Tucker564f19e2003-12-09 19:18:07 +110066 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits);
67 } else {
Damien Miller8e7fb332003-02-24 12:03:03 +110068 /* 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);
Darren Tucker564f19e2003-12-09 19:18:07 +110075
76 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
77 min, nbits, max);
Damien Miller8e7fb332003-02-24 12:03:03 +110078 }
79#ifdef DEBUG_KEXDH
80 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
81 min, nbits, max);
82#endif
83 packet_send();
84
85 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
86 packet_read_expect(SSH2_MSG_KEX_DH_GEX_GROUP);
87
88 if ((p = BN_new()) == NULL)
89 fatal("BN_new");
90 packet_get_bignum2(p);
91 if ((g = BN_new()) == NULL)
92 fatal("BN_new");
93 packet_get_bignum2(g);
94 packet_check_eom();
95
96 if (BN_num_bits(p) < min || BN_num_bits(p) > max)
97 fatal("DH_GEX group out of range: %d !< %d !< %d",
98 min, BN_num_bits(p), max);
99
100 dh = dh_new_group(g, p);
101 dh_gen_key(dh, kex->we_need * 8);
102
103#ifdef DEBUG_KEXDH
104 DHparams_print_fp(stderr, dh);
105 fprintf(stderr, "pub= ");
106 BN_print_fp(stderr, dh->pub_key);
107 fprintf(stderr, "\n");
108#endif
109
110 debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
111 /* generate and send 'e', client DH public key */
112 packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
113 packet_put_bignum2(dh->pub_key);
114 packet_send();
115
116 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
117 packet_read_expect(SSH2_MSG_KEX_DH_GEX_REPLY);
118
119 /* key, cert */
120 server_host_key_blob = packet_get_string(&sbloblen);
121 server_host_key = key_from_blob(server_host_key_blob, sbloblen);
122 if (server_host_key == NULL)
123 fatal("cannot decode server_host_key_blob");
124 if (server_host_key->type != kex->hostkey_type)
125 fatal("type mismatch for decoded server_host_key_blob");
126 if (kex->verify_host_key == NULL)
127 fatal("cannot verify server_host_key");
128 if (kex->verify_host_key(server_host_key) == -1)
129 fatal("server_host_key verification failed");
130
Damien Millerad6b14d2006-06-13 13:00:41 +1000131 /* DH parameter f, server public DH key */
Damien Miller8e7fb332003-02-24 12:03:03 +1100132 if ((dh_server_pub = BN_new()) == NULL)
133 fatal("dh_server_pub == NULL");
134 packet_get_bignum2(dh_server_pub);
135
136#ifdef DEBUG_KEXDH
137 fprintf(stderr, "dh_server_pub= ");
138 BN_print_fp(stderr, dh_server_pub);
139 fprintf(stderr, "\n");
140 debug("bits %d", BN_num_bits(dh_server_pub));
141#endif
142
143 /* signed H */
144 signature = packet_get_string(&slen);
145 packet_check_eom();
146
147 if (!dh_pub_is_valid(dh, dh_server_pub))
148 packet_disconnect("bad server public DH value");
149
150 klen = DH_size(dh);
151 kbuf = xmalloc(klen);
152 kout = DH_compute_key(kbuf, dh_server_pub, dh);
153#ifdef DEBUG_KEXDH
154 dump_digest("shared secret", kbuf, kout);
155#endif
156 if ((shared_secret = BN_new()) == NULL)
157 fatal("kexgex_client: BN_new failed");
158 BN_bin2bn(kbuf, kout, shared_secret);
159 memset(kbuf, 0, klen);
160 xfree(kbuf);
161
162 if (datafellows & SSH_OLD_DHGEX)
163 min = max = -1;
164
165 /* calc and verify H */
Damien Miller19bb3a52005-11-05 15:19:35 +1100166 kexgex_hash(
167 kex->evp_md,
Damien Miller8e7fb332003-02-24 12:03:03 +1100168 kex->client_version_string,
169 kex->server_version_string,
170 buffer_ptr(&kex->my), buffer_len(&kex->my),
171 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
172 server_host_key_blob, sbloblen,
173 min, nbits, max,
174 dh->p, dh->g,
175 dh->pub_key,
176 dh_server_pub,
Damien Miller19bb3a52005-11-05 15:19:35 +1100177 shared_secret,
178 &hash, &hashlen
Damien Miller8e7fb332003-02-24 12:03:03 +1100179 );
Damien Miller19bb3a52005-11-05 15:19:35 +1100180
Damien Miller8e7fb332003-02-24 12:03:03 +1100181 /* have keys, free DH */
182 DH_free(dh);
183 xfree(server_host_key_blob);
184 BN_clear_free(dh_server_pub);
185
Damien Miller19bb3a52005-11-05 15:19:35 +1100186 if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
Damien Miller8e7fb332003-02-24 12:03:03 +1100187 fatal("key_verify failed for server_host_key");
188 key_free(server_host_key);
189 xfree(signature);
190
191 /* save session id */
192 if (kex->session_id == NULL) {
Damien Miller19bb3a52005-11-05 15:19:35 +1100193 kex->session_id_len = hashlen;
Damien Miller8e7fb332003-02-24 12:03:03 +1100194 kex->session_id = xmalloc(kex->session_id_len);
195 memcpy(kex->session_id, hash, kex->session_id_len);
196 }
Damien Miller19bb3a52005-11-05 15:19:35 +1100197 kex_derive_keys(kex, hash, hashlen, shared_secret);
Damien Miller8e7fb332003-02-24 12:03:03 +1100198 BN_clear_free(shared_secret);
199
200 kex_finish(kex);
201}