1 /* $OpenBSD: kexecdhs.c,v 1.2 2010/09/22 05:01:29 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 #include <string.h>
31 #include <signal.h>
32
33 #include "xmalloc.h"
34 #include "buffer.h"
35 #include "key.h"
36 #include "cipher.h"
37 #include "kex.h"
38 #include "log.h"
39 #include "packet.h"
40 #include "dh.h"
41 #include "ssh2.h"
42 #ifdef GSSAPI
43 #include "ssh-gss.h"
44 #endif
45 #include "monitor_wrap.h"
46
47 #ifdef OPENSSL_HAS_ECC
48
49 #include <openssl/ecdh.h>
50
51 void
kexecdh_server(Kex * kex)52 kexecdh_server(Kex *kex)
53 {
54 EC_POINT *client_public;
55 EC_KEY *server_key;
56 const EC_GROUP *group;
57 BIGNUM *shared_secret;
58 Key *server_host_private, *server_host_public;
59 u_char *server_host_key_blob = NULL, *signature = NULL;
60 u_char *kbuf, *hash;
61 u_int klen, slen, sbloblen, hashlen;
62 int curve_nid;
63
64 if ((curve_nid = kex_ecdh_name_to_nid(kex->name)) == -1)
65 fatal("%s: unsupported ECDH curve \"%s\"", __func__, kex->name);
66 if ((server_key = EC_KEY_new_by_curve_name(curve_nid)) == NULL)
67 fatal("%s: EC_KEY_new_by_curve_name failed", __func__);
68 if (EC_KEY_generate_key(server_key) != 1)
69 fatal("%s: EC_KEY_generate_key failed", __func__);
70 group = EC_KEY_get0_group(server_key);
71
72 #ifdef DEBUG_KEXECDH
73 fputs("server private key:\n", stderr);
74 key_dump_ec_key(server_key);
75 #endif
76
77 if (kex->load_host_public_key == NULL ||
78 kex->load_host_private_key == NULL)
79 fatal("Cannot load hostkey");
80 server_host_public = kex->load_host_public_key(kex->hostkey_type);
81 if (server_host_public == NULL)
82 fatal("Unsupported hostkey type %d", kex->hostkey_type);
83 server_host_private = kex->load_host_private_key(kex->hostkey_type);
84 if (server_host_private == NULL)
85 fatal("Missing private key for hostkey type %d",
86 kex->hostkey_type);
87
88 debug("expecting SSH2_MSG_KEX_ECDH_INIT");
89 packet_read_expect(SSH2_MSG_KEX_ECDH_INIT);
90 if ((client_public = EC_POINT_new(group)) == NULL)
91 fatal("%s: EC_POINT_new failed", __func__);
92 packet_get_ecpoint(group, client_public);
93 packet_check_eom();
94
95 if (key_ec_validate_public(group, client_public) != 0)
96 fatal("%s: invalid client public key", __func__);
97
98 #ifdef DEBUG_KEXECDH
99 fputs("client public key:\n", stderr);
100 key_dump_ec_point(group, client_public);
101 #endif
102
103 /* Calculate shared_secret */
104 klen = (EC_GROUP_get_degree(group) + 7) / 8;
105 kbuf = xmalloc(klen);
106 if (ECDH_compute_key(kbuf, klen, client_public,
107 server_key, NULL) != (int)klen)
108 fatal("%s: ECDH_compute_key failed", __func__);
109
110 #ifdef DEBUG_KEXDH
111 dump_digest("shared secret", kbuf, klen);
112 #endif
113 if ((shared_secret = BN_new()) == NULL)
114 fatal("%s: BN_new failed", __func__);
115 if (BN_bin2bn(kbuf, klen, shared_secret) == NULL)
116 fatal("%s: BN_bin2bn failed", __func__);
117 memset(kbuf, 0, klen);
118 xfree(kbuf);
119
120 /* calc H */
121 key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
122 kex_ecdh_hash(
123 kex->evp_md,
124 group,
125 kex->client_version_string,
126 kex->server_version_string,
127 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
128 buffer_ptr(&kex->my), buffer_len(&kex->my),
129 server_host_key_blob, sbloblen,
130 client_public,
131 EC_KEY_get0_public_key(server_key),
132 shared_secret,
133 &hash, &hashlen
134 );
135 EC_POINT_clear_free(client_public);
136
137 /* save session id := H */
138 if (kex->session_id == NULL) {
139 kex->session_id_len = hashlen;
140 kex->session_id = xmalloc(kex->session_id_len);
141 memcpy(kex->session_id, hash, kex->session_id_len);
142 }
143
144 /* sign H */
145 if (PRIVSEP(key_sign(server_host_private, &signature, &slen,
146 hash, hashlen)) < 0)
147 fatal("kexdh_server: key_sign failed");
148
149 /* destroy_sensitive_data(); */
150
151 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
152 packet_start(SSH2_MSG_KEX_ECDH_REPLY);
153 packet_put_string(server_host_key_blob, sbloblen);
154 packet_put_ecpoint(group, EC_KEY_get0_public_key(server_key));
155 packet_put_string(signature, slen);
156 packet_send();
157
158 xfree(signature);
159 xfree(server_host_key_blob);
160 /* have keys, free server key */
161 EC_KEY_free(server_key);
162
163 kex_derive_keys(kex, hash, hashlen, shared_secret);
164 BN_clear_free(shared_secret);
165 kex_finish(kex);
166 }
167 #else /* OPENSSL_HAS_ECC */
168 void
kexecdh_server(Kex * kex)169 kexecdh_server(Kex *kex)
170 {
171 fatal("ECC support is not enabled");
172 }
173 #endif /* OPENSSL_HAS_ECC */
174