1 /* $OpenBSD: kexdhc.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 <openssl/dh.h>
31
32 #include <stdarg.h>
33 #include <stdio.h>
34 #include <string.h>
35 #include <signal.h>
36
37 #include "xmalloc.h"
38 #include "buffer.h"
39 #include "key.h"
40 #include "cipher.h"
41 #include "kex.h"
42 #include "log.h"
43 #include "packet.h"
44 #include "dh.h"
45 #include "ssh2.h"
46
47 void
kexdh_client(Kex * kex)48 kexdh_client(Kex *kex)
49 {
50 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
51 DH *dh;
52 Key *server_host_key;
53 u_char *server_host_key_blob = NULL, *signature = NULL;
54 u_char *kbuf, *hash;
55 u_int klen, slen, sbloblen, hashlen;
56 int kout;
57
58 /* generate and send 'e', client DH public key */
59 switch (kex->kex_type) {
60 case KEX_DH_GRP1_SHA1:
61 dh = dh_new_group1();
62 break;
63 case KEX_DH_GRP14_SHA1:
64 dh = dh_new_group14();
65 break;
66 default:
67 fatal("%s: Unexpected KEX type %d", __func__, kex->kex_type);
68 }
69 dh_gen_key(dh, kex->we_need * 8);
70 packet_start(SSH2_MSG_KEXDH_INIT);
71 packet_put_bignum2(dh->pub_key);
72 packet_send();
73
74 debug("sending SSH2_MSG_KEXDH_INIT");
75 #ifdef DEBUG_KEXDH
76 DHparams_print_fp(stderr, dh);
77 fprintf(stderr, "pub= ");
78 BN_print_fp(stderr, dh->pub_key);
79 fprintf(stderr, "\n");
80 #endif
81
82 debug("expecting SSH2_MSG_KEXDH_REPLY");
83 packet_read_expect(SSH2_MSG_KEXDH_REPLY);
84
85 /* key, cert */
86 server_host_key_blob = packet_get_string(&sbloblen);
87 server_host_key = key_from_blob(server_host_key_blob, sbloblen);
88 if (server_host_key == NULL)
89 fatal("cannot decode server_host_key_blob");
90 if (server_host_key->type != kex->hostkey_type)
91 fatal("type mismatch for decoded server_host_key_blob");
92 if (kex->verify_host_key == NULL)
93 fatal("cannot verify server_host_key");
94 if (kex->verify_host_key(server_host_key) == -1)
95 fatal("server_host_key verification failed");
96
97 /* DH parameter f, server public DH key */
98 if ((dh_server_pub = BN_new()) == NULL)
99 fatal("dh_server_pub == NULL");
100 packet_get_bignum2(dh_server_pub);
101
102 #ifdef DEBUG_KEXDH
103 fprintf(stderr, "dh_server_pub= ");
104 BN_print_fp(stderr, dh_server_pub);
105 fprintf(stderr, "\n");
106 debug("bits %d", BN_num_bits(dh_server_pub));
107 #endif
108
109 /* signed H */
110 signature = packet_get_string(&slen);
111 packet_check_eom();
112
113 if (!dh_pub_is_valid(dh, dh_server_pub))
114 packet_disconnect("bad server public DH value");
115
116 klen = DH_size(dh);
117 kbuf = xmalloc(klen);
118 if ((kout = DH_compute_key(kbuf, dh_server_pub, dh)) < 0)
119 fatal("DH_compute_key: failed");
120 #ifdef DEBUG_KEXDH
121 dump_digest("shared secret", kbuf, kout);
122 #endif
123 if ((shared_secret = BN_new()) == NULL)
124 fatal("kexdh_client: BN_new failed");
125 if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
126 fatal("kexdh_client: BN_bin2bn failed");
127 memset(kbuf, 0, klen);
128 xfree(kbuf);
129
130 /* calc and verify H */
131 kex_dh_hash(
132 kex->client_version_string,
133 kex->server_version_string,
134 buffer_ptr(&kex->my), buffer_len(&kex->my),
135 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
136 server_host_key_blob, sbloblen,
137 dh->pub_key,
138 dh_server_pub,
139 shared_secret,
140 &hash, &hashlen
141 );
142 xfree(server_host_key_blob);
143 BN_clear_free(dh_server_pub);
144 DH_free(dh);
145
146 if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
147 fatal("key_verify failed for server_host_key");
148 key_free(server_host_key);
149 xfree(signature);
150
151 /* save session id */
152 if (kex->session_id == NULL) {
153 kex->session_id_len = hashlen;
154 kex->session_id = xmalloc(kex->session_id_len);
155 memcpy(kex->session_id, hash, kex->session_id_len);
156 }
157
158 kex_derive_keys(kex, hash, hashlen, shared_secret);
159 BN_clear_free(shared_secret);
160 kex_finish(kex);
161 }
162