1 /*
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"
26 RCSID("$OpenBSD: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $");
27
28 #pragma ident "%Z%%M% %I% %E% SMI"
29
30 #include <openssl/crypto.h>
31 #include <openssl/bn.h>
32
33 #include "xmalloc.h"
34 #include "buffer.h"
35 #include "bufaux.h"
36 #include "key.h"
37 #include "kex.h"
38 #include "log.h"
39 #include "packet.h"
40 #include "dh.h"
41 #include "ssh2.h"
42
43 void
kexdh_client(Kex * kex)44 kexdh_client(Kex *kex)
45 {
46 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
47 DH *dh;
48 Key *server_host_key;
49 u_char *server_host_key_blob = NULL, *signature = NULL;
50 u_char *kbuf, *hash;
51 u_int klen, kout, slen, sbloblen;
52
53 /* generate and send 'e', client DH public key */
54 dh = dh_new_group1();
55 dh_gen_key(dh, kex->we_need * 8);
56 packet_start(SSH2_MSG_KEXDH_INIT);
57 packet_put_bignum2(dh->pub_key);
58 packet_send();
59
60 debug("sending SSH2_MSG_KEXDH_INIT");
61 #ifdef DEBUG_KEXDH
62 DHparams_print_fp(stderr, dh);
63 fprintf(stderr, "pub= ");
64 BN_print_fp(stderr, dh->pub_key);
65 fprintf(stderr, "\n");
66 #endif
67
68 debug("expecting SSH2_MSG_KEXDH_REPLY");
69 packet_read_expect(SSH2_MSG_KEXDH_REPLY);
70
71 /* key, cert */
72 server_host_key_blob = packet_get_string(&sbloblen);
73 server_host_key = key_from_blob(server_host_key_blob, sbloblen);
74 if (server_host_key == NULL)
75 fatal("cannot decode server_host_key_blob");
76 if (server_host_key->type != kex->hostkey_type)
77 fatal("type mismatch for decoded server_host_key_blob");
78 if (kex->verify_host_key == NULL)
79 fatal("cannot verify server_host_key");
80 if (kex->verify_host_key(server_host_key) == -1)
81 fatal("server_host_key verification failed");
82
83 /* DH paramter f, server public DH key */
84 if ((dh_server_pub = BN_new()) == NULL)
85 fatal("dh_server_pub == NULL");
86 packet_get_bignum2(dh_server_pub);
87
88 #ifdef DEBUG_KEXDH
89 fprintf(stderr, "dh_server_pub= ");
90 BN_print_fp(stderr, dh_server_pub);
91 fprintf(stderr, "\n");
92 debug("bits %d", BN_num_bits(dh_server_pub));
93 #endif
94
95 /* signed H */
96 signature = packet_get_string(&slen);
97 packet_check_eom();
98
99 if (!dh_pub_is_valid(dh, dh_server_pub))
100 packet_disconnect("bad server public DH value");
101
102 klen = DH_size(dh);
103 kbuf = xmalloc(klen);
104 kout = DH_compute_key(kbuf, dh_server_pub, dh);
105 #ifdef DEBUG_KEXDH
106 dump_digest("shared secret", kbuf, kout);
107 #endif
108 if ((shared_secret = BN_new()) == NULL)
109 fatal("kexdh_client: BN_new failed");
110 BN_bin2bn(kbuf, kout, shared_secret);
111 memset(kbuf, 0, klen);
112 xfree(kbuf);
113
114 /* calc and verify H */
115 hash = kex_dh_hash(
116 kex->client_version_string,
117 kex->server_version_string,
118 buffer_ptr(&kex->my), buffer_len(&kex->my),
119 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
120 server_host_key_blob, sbloblen,
121 dh->pub_key,
122 dh_server_pub,
123 shared_secret
124 );
125 xfree(server_host_key_blob);
126 BN_clear_free(dh_server_pub);
127 DH_free(dh);
128
129 if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
130 fatal("key_verify failed for server_host_key");
131 key_free(server_host_key);
132 xfree(signature);
133
134 /* save session id */
135 if (kex->session_id == NULL) {
136 kex->session_id_len = 20;
137 kex->session_id = xmalloc(kex->session_id_len);
138 memcpy(kex->session_id, hash, kex->session_id_len);
139 }
140
141 kex_derive_keys(kex, hash, shared_secret);
142 BN_clear_free(shared_secret);
143 kex_finish(kex);
144 }
145