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Damien Miller8e7fb332003-02-24 12:03:03 +11001/*
2 * Copyright (c) 2001 Markus Friedl. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23 */
24
25#include "includes.h"
Damien Miller19bb3a52005-11-05 15:19:35 +110026RCSID("$OpenBSD: kexdhs.c,v 1.3 2005/11/04 05:15:59 djm Exp $");
Damien Miller8e7fb332003-02-24 12:03:03 +110027
28#include "xmalloc.h"
29#include "key.h"
30#include "kex.h"
31#include "log.h"
32#include "packet.h"
33#include "dh.h"
34#include "ssh2.h"
35#include "monitor_wrap.h"
36
37void
38kexdh_server(Kex *kex)
39{
40 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
41 DH *dh;
42 Key *server_host_key;
43 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
Damien Miller19bb3a52005-11-05 15:19:35 +110044 u_int sbloblen, klen, kout, hashlen;
Damien Miller8e7fb332003-02-24 12:03:03 +110045 u_int slen;
46
47 /* generate server DH public key */
Damien Millerf675fc42004-06-15 10:30:09 +100048 switch (kex->kex_type) {
49 case KEX_DH_GRP1_SHA1:
50 dh = dh_new_group1();
51 break;
52 case KEX_DH_GRP14_SHA1:
53 dh = dh_new_group14();
54 break;
55 default:
56 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
57 }
Damien Miller8e7fb332003-02-24 12:03:03 +110058 dh_gen_key(dh, kex->we_need * 8);
59
60 debug("expecting SSH2_MSG_KEXDH_INIT");
61 packet_read_expect(SSH2_MSG_KEXDH_INIT);
62
63 if (kex->load_host_key == NULL)
64 fatal("Cannot load hostkey");
65 server_host_key = kex->load_host_key(kex->hostkey_type);
66 if (server_host_key == NULL)
67 fatal("Unsupported hostkey type %d", kex->hostkey_type);
68
69 /* key, cert */
70 if ((dh_client_pub = BN_new()) == NULL)
71 fatal("dh_client_pub == NULL");
72 packet_get_bignum2(dh_client_pub);
73 packet_check_eom();
74
75#ifdef DEBUG_KEXDH
76 fprintf(stderr, "dh_client_pub= ");
77 BN_print_fp(stderr, dh_client_pub);
78 fprintf(stderr, "\n");
79 debug("bits %d", BN_num_bits(dh_client_pub));
80#endif
81
82#ifdef DEBUG_KEXDH
83 DHparams_print_fp(stderr, dh);
84 fprintf(stderr, "pub= ");
85 BN_print_fp(stderr, dh->pub_key);
86 fprintf(stderr, "\n");
87#endif
88 if (!dh_pub_is_valid(dh, dh_client_pub))
89 packet_disconnect("bad client public DH value");
90
91 klen = DH_size(dh);
92 kbuf = xmalloc(klen);
93 kout = DH_compute_key(kbuf, dh_client_pub, dh);
94#ifdef DEBUG_KEXDH
95 dump_digest("shared secret", kbuf, kout);
96#endif
97 if ((shared_secret = BN_new()) == NULL)
98 fatal("kexdh_server: BN_new failed");
99 BN_bin2bn(kbuf, kout, shared_secret);
100 memset(kbuf, 0, klen);
101 xfree(kbuf);
102
103 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
104
105 /* calc H */
Damien Miller19bb3a52005-11-05 15:19:35 +1100106 kex_dh_hash(
Damien Miller8e7fb332003-02-24 12:03:03 +1100107 kex->client_version_string,
108 kex->server_version_string,
109 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
110 buffer_ptr(&kex->my), buffer_len(&kex->my),
111 server_host_key_blob, sbloblen,
112 dh_client_pub,
113 dh->pub_key,
Damien Miller19bb3a52005-11-05 15:19:35 +1100114 shared_secret,
115 &hash, &hashlen
Damien Miller8e7fb332003-02-24 12:03:03 +1100116 );
117 BN_clear_free(dh_client_pub);
118
119 /* save session id := H */
Damien Miller8e7fb332003-02-24 12:03:03 +1100120 if (kex->session_id == NULL) {
Damien Miller19bb3a52005-11-05 15:19:35 +1100121 kex->session_id_len = hashlen;
Damien Miller8e7fb332003-02-24 12:03:03 +1100122 kex->session_id = xmalloc(kex->session_id_len);
123 memcpy(kex->session_id, hash, kex->session_id_len);
124 }
125
126 /* sign H */
Damien Miller19bb3a52005-11-05 15:19:35 +1100127 PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, hashlen));
Damien Miller8e7fb332003-02-24 12:03:03 +1100128
129 /* destroy_sensitive_data(); */
130
131 /* send server hostkey, DH pubkey 'f' and singed H */
132 packet_start(SSH2_MSG_KEXDH_REPLY);
133 packet_put_string(server_host_key_blob, sbloblen);
134 packet_put_bignum2(dh->pub_key); /* f */
135 packet_put_string(signature, slen);
136 packet_send();
137
138 xfree(signature);
139 xfree(server_host_key_blob);
140 /* have keys, free DH */
141 DH_free(dh);
142
Damien Miller19bb3a52005-11-05 15:19:35 +1100143 kex_derive_keys(kex, hash, hashlen, shared_secret);
Damien Miller8e7fb332003-02-24 12:03:03 +1100144 BN_clear_free(shared_secret);
145 kex_finish(kex);
146}