1 /* $OpenBSD: kexdhs.c,v 1.12 2010/11/10 01:33:07 djm Exp $ */
2 /*
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
28 #include <sys/types.h>
29
30 #include <stdarg.h>
31 #include <string.h>
32 #include <signal.h>
33
34 #include <openssl/dh.h>
35
36 #include "xmalloc.h"
37 #include "buffer.h"
38 #include "key.h"
39 #include "cipher.h"
40 #include "kex.h"
41 #include "log.h"
42 #include "packet.h"
43 #include "dh.h"
44 #include "ssh2.h"
45 #ifdef GSSAPI
46 #include "ssh-gss.h"
47 #endif
48 #include "monitor_wrap.h"
49
50 void
kexdh_server(Kex * kex)51 kexdh_server(Kex *kex)
52 {
53 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
54 DH *dh;
55 Key *server_host_public, *server_host_private;
56 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
57 u_int sbloblen, klen, hashlen, slen;
58 int kout;
59
60 /* generate server DH public key */
61 switch (kex->kex_type) {
62 case KEX_DH_GRP1_SHA1:
63 dh = dh_new_group1();
64 break;
65 case KEX_DH_GRP14_SHA1:
66 dh = dh_new_group14();
67 break;
68 default:
69 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
70 }
71 dh_gen_key(dh, kex->we_need * 8);
72
73 debug("expecting SSH2_MSG_KEXDH_INIT");
74 packet_read_expect(SSH2_MSG_KEXDH_INIT);
75
76 if (kex->load_host_public_key == NULL ||
77 kex->load_host_private_key == NULL)
78 fatal("Cannot load hostkey");
79 server_host_public = kex->load_host_public_key(kex->hostkey_type);
80 if (server_host_public == NULL)
81 fatal("Unsupported hostkey type %d", kex->hostkey_type);
82 server_host_private = kex->load_host_private_key(kex->hostkey_type);
83 if (server_host_private == NULL)
84 fatal("Missing private key for hostkey type %d",
85 kex->hostkey_type);
86
87 /* key, cert */
88 if ((dh_client_pub = BN_new()) == NULL)
89 fatal("dh_client_pub == NULL");
90 packet_get_bignum2(dh_client_pub);
91 packet_check_eom();
92
93 #ifdef DEBUG_KEXDH
94 fprintf(stderr, "dh_client_pub= ");
95 BN_print_fp(stderr, dh_client_pub);
96 fprintf(stderr, "\n");
97 debug("bits %d", BN_num_bits(dh_client_pub));
98 #endif
99
100 #ifdef DEBUG_KEXDH
101 DHparams_print_fp(stderr, dh);
102 fprintf(stderr, "pub= ");
103 BN_print_fp(stderr, dh->pub_key);
104 fprintf(stderr, "\n");
105 #endif
106 if (!dh_pub_is_valid(dh, dh_client_pub))
107 packet_disconnect("bad client public DH value");
108
109 klen = DH_size(dh);
110 kbuf = xmalloc(klen);
111 if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
112 fatal("DH_compute_key: failed");
113 #ifdef DEBUG_KEXDH
114 dump_digest("shared secret", kbuf, kout);
115 #endif
116 if ((shared_secret = BN_new()) == NULL)
117 fatal("kexdh_server: BN_new failed");
118 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
119 fatal("kexdh_server: BN_bin2bn failed");
120 memset(kbuf, 0, klen);
121 xfree(kbuf);
122
123 key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
124
125 /* calc H */
126 kex_dh_hash(
127 kex->client_version_string,
128 kex->server_version_string,
129 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
130 buffer_ptr(&kex->my), buffer_len(&kex->my),
131 server_host_key_blob, sbloblen,
132 dh_client_pub,
133 dh->pub_key,
134 shared_secret,
135 &hash, &hashlen
136 );
137 BN_clear_free(dh_client_pub);
138
139 /* save session id := H */
140 if (kex->session_id == NULL) {
141 kex->session_id_len = hashlen;
142 kex->session_id = xmalloc(kex->session_id_len);
143 memcpy(kex->session_id, hash, kex->session_id_len);
144 }
145
146 /* sign H */
147 if (PRIVSEP(key_sign(server_host_private, &signature, &slen, hash,
148 hashlen)) < 0)
149 fatal("kexdh_server: key_sign failed");
150
151 /* destroy_sensitive_data(); */
152
153 /* send server hostkey, DH pubkey 'f' and singed H */
154 packet_start(SSH2_MSG_KEXDH_REPLY);
155 packet_put_string(server_host_key_blob, sbloblen);
156 packet_put_bignum2(dh->pub_key); /* f */
157 packet_put_string(signature, slen);
158 packet_send();
159
160 xfree(signature);
161 xfree(server_host_key_blob);
162 /* have keys, free DH */
163 DH_free(dh);
164
165 kex_derive_keys(kex, hash, hashlen, shared_secret);
166 BN_clear_free(shared_secret);
167 kex_finish(kex);
168 }
169