1 /* $OpenBSD: kexecdhc.c,v 1.7 2014/02/02 03:44:31 djm Exp $ */
2 /*
3 * Copyright (c) 2001 Markus Friedl. All rights reserved.
4 * Copyright (c) 2010 Damien Miller. 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"
28
29 #include <sys/types.h>
30
31 #include <stdio.h>
32 #include <string.h>
33 #include <signal.h>
34
35 #include "xmalloc.h"
36 #include "buffer.h"
37 #include "key.h"
38 #include "cipher.h"
39 #include "kex.h"
40 #include "log.h"
41 #include "packet.h"
42 #include "dh.h"
43 #include "ssh2.h"
44
45 #ifdef OPENSSL_HAS_ECC
46
47 #include <openssl/ecdh.h>
48
49 void
kexecdh_client(Kex * kex)50 kexecdh_client(Kex *kex)
51 {
52 EC_KEY *client_key;
53 EC_POINT *server_public;
54 const EC_GROUP *group;
55 BIGNUM *shared_secret;
56 Key *server_host_key;
57 u_char *server_host_key_blob = NULL, *signature = NULL;
58 u_char *kbuf, *hash;
59 u_int klen, slen, sbloblen, hashlen;
60
61 if ((client_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL)
62 fatal("%s: EC_KEY_new_by_curve_name failed", __func__);
63 if (EC_KEY_generate_key(client_key) != 1)
64 fatal("%s: EC_KEY_generate_key failed", __func__);
65 group = EC_KEY_get0_group(client_key);
66
67 packet_start(SSH2_MSG_KEX_ECDH_INIT);
68 packet_put_ecpoint(group, EC_KEY_get0_public_key(client_key));
69 packet_send();
70 debug("sending SSH2_MSG_KEX_ECDH_INIT");
71
72 #ifdef DEBUG_KEXECDH
73 fputs("client private key:\n", stderr);
74 key_dump_ec_key(client_key);
75 #endif
76
77 debug("expecting SSH2_MSG_KEX_ECDH_REPLY");
78 packet_read_expect(SSH2_MSG_KEX_ECDH_REPLY);
79
80 /* hostkey */
81 server_host_key_blob = packet_get_string(&sbloblen);
82 server_host_key = key_from_blob(server_host_key_blob, sbloblen);
83 if (server_host_key == NULL)
84 fatal("cannot decode server_host_key_blob");
85 if (server_host_key->type != kex->hostkey_type)
86 fatal("type mismatch for decoded server_host_key_blob");
87 if (kex->verify_host_key == NULL)
88 fatal("cannot verify server_host_key");
89 if (kex->verify_host_key(server_host_key) == -1)
90 fatal("server_host_key verification failed");
91
92 /* Q_S, server public key */
93 if ((server_public = EC_POINT_new(group)) == NULL)
94 fatal("%s: EC_POINT_new failed", __func__);
95 packet_get_ecpoint(group, server_public);
96
97 if (key_ec_validate_public(group, server_public) != 0)
98 fatal("%s: invalid server public key", __func__);
99
100 #ifdef DEBUG_KEXECDH
101 fputs("server public key:\n", stderr);
102 key_dump_ec_point(group, server_public);
103 #endif
104
105 /* signed H */
106 signature = packet_get_string(&slen);
107 packet_check_eom();
108
109 klen = (EC_GROUP_get_degree(group) + 7) / 8;
110 kbuf = xmalloc(klen);
111 if (ECDH_compute_key(kbuf, klen, server_public,
112 client_key, NULL) != (int)klen)
113 fatal("%s: ECDH_compute_key failed", __func__);
114
115 #ifdef DEBUG_KEXECDH
116 dump_digest("shared secret", kbuf, klen);
117 #endif
118 if ((shared_secret = BN_new()) == NULL)
119 fatal("%s: BN_new failed", __func__);
120 if (BN_bin2bn(kbuf, klen, shared_secret) == NULL)
121 fatal("%s: BN_bin2bn failed", __func__);
122 explicit_bzero(kbuf, klen);
123 free(kbuf);
124
125 /* calc and verify H */
126 kex_ecdh_hash(
127 kex->hash_alg,
128 group,
129 kex->client_version_string,
130 kex->server_version_string,
131 buffer_ptr(&kex->my), buffer_len(&kex->my),
132 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
133 server_host_key_blob, sbloblen,
134 EC_KEY_get0_public_key(client_key),
135 server_public,
136 shared_secret,
137 &hash, &hashlen
138 );
139 free(server_host_key_blob);
140 EC_POINT_clear_free(server_public);
141 EC_KEY_free(client_key);
142
143 if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1)
144 fatal("key_verify failed for server_host_key");
145 key_free(server_host_key);
146 free(signature);
147
148 /* save session id */
149 if (kex->session_id == NULL) {
150 kex->session_id_len = hashlen;
151 kex->session_id = xmalloc(kex->session_id_len);
152 memcpy(kex->session_id, hash, kex->session_id_len);
153 }
154
155 kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
156 BN_clear_free(shared_secret);
157 kex_finish(kex);
158 }
159 #else /* OPENSSL_HAS_ECC */
160 void
kexecdh_client(Kex * kex)161 kexecdh_client(Kex *kex)
162 {
163 fatal("ECC support is not enabled");
164 }
165 #endif /* OPENSSL_HAS_ECC */
166