1 /* $OpenBSD: kexecdhs.c,v 1.15 2015/12/04 16:41:28 markus 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 #if defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC)
30
31 #include <sys/types.h>
32 #include <string.h>
33 #include <signal.h>
34
35 #include <openssl/ecdh.h>
36
37 #include "sshkey.h"
38 #include "cipher.h"
39 #include "digest.h"
40 #include "kex.h"
41 #include "log.h"
42 #include "packet.h"
43 #include "ssh2.h"
44
45 #include "dispatch.h"
46 #include "compat.h"
47 #include "ssherr.h"
48 #include "sshbuf.h"
49
50 static int input_kex_ecdh_init(int, u_int32_t, void *);
51
52 int
kexecdh_server(struct ssh * ssh)53 kexecdh_server(struct ssh *ssh)
54 {
55 debug("expecting SSH2_MSG_KEX_ECDH_INIT");
56 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_ecdh_init);
57 return 0;
58 }
59
60 static int
input_kex_ecdh_init(int type,u_int32_t seq,void * ctxt)61 input_kex_ecdh_init(int type, u_int32_t seq, void *ctxt)
62 {
63 struct ssh *ssh = ctxt;
64 struct kex *kex = ssh->kex;
65 EC_POINT *client_public;
66 EC_KEY *server_key = NULL;
67 const EC_GROUP *group;
68 const EC_POINT *public_key;
69 BIGNUM *shared_secret = NULL;
70 struct sshkey *server_host_private, *server_host_public;
71 u_char *server_host_key_blob = NULL, *signature = NULL;
72 u_char *kbuf = NULL;
73 u_char hash[SSH_DIGEST_MAX_LENGTH];
74 size_t slen, sbloblen;
75 size_t klen = 0, hashlen;
76 int r;
77
78 if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
79 r = SSH_ERR_ALLOC_FAIL;
80 goto out;
81 }
82 if (EC_KEY_generate_key(server_key) != 1) {
83 r = SSH_ERR_LIBCRYPTO_ERROR;
84 goto out;
85 }
86 group = EC_KEY_get0_group(server_key);
87
88 #ifdef DEBUG_KEXECDH
89 fputs("server private key:\n", stderr);
90 sshkey_dump_ec_key(server_key);
91 #endif
92
93 if (kex->load_host_public_key == NULL ||
94 kex->load_host_private_key == NULL) {
95 r = SSH_ERR_INVALID_ARGUMENT;
96 goto out;
97 }
98 server_host_public = kex->load_host_public_key(kex->hostkey_type,
99 kex->hostkey_nid, ssh);
100 server_host_private = kex->load_host_private_key(kex->hostkey_type,
101 kex->hostkey_nid, ssh);
102 if (server_host_public == NULL) {
103 r = SSH_ERR_NO_HOSTKEY_LOADED;
104 goto out;
105 }
106 if ((client_public = EC_POINT_new(group)) == NULL) {
107 r = SSH_ERR_ALLOC_FAIL;
108 goto out;
109 }
110 if ((r = sshpkt_get_ec(ssh, client_public, group)) != 0 ||
111 (r = sshpkt_get_end(ssh)) != 0)
112 goto out;
113
114 #ifdef DEBUG_KEXECDH
115 fputs("client public key:\n", stderr);
116 sshkey_dump_ec_point(group, client_public);
117 #endif
118 if (sshkey_ec_validate_public(group, client_public) != 0) {
119 sshpkt_disconnect(ssh, "invalid client public key");
120 r = SSH_ERR_MESSAGE_INCOMPLETE;
121 goto out;
122 }
123
124 /* Calculate shared_secret */
125 klen = (EC_GROUP_get_degree(group) + 7) / 8;
126 if ((kbuf = malloc(klen)) == NULL ||
127 (shared_secret = BN_new()) == NULL) {
128 r = SSH_ERR_ALLOC_FAIL;
129 goto out;
130 }
131 if (ECDH_compute_key(kbuf, klen, client_public,
132 server_key, NULL) != (int)klen ||
133 BN_bin2bn(kbuf, klen, shared_secret) == NULL) {
134 r = SSH_ERR_LIBCRYPTO_ERROR;
135 goto out;
136 }
137
138 #ifdef DEBUG_KEXECDH
139 dump_digest("shared secret", kbuf, klen);
140 #endif
141 /* calc H */
142 if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
143 &sbloblen)) != 0)
144 goto out;
145 hashlen = sizeof(hash);
146 if ((r = kex_ecdh_hash(
147 kex->hash_alg,
148 group,
149 kex->client_version_string,
150 kex->server_version_string,
151 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
152 sshbuf_ptr(kex->my), sshbuf_len(kex->my),
153 server_host_key_blob, sbloblen,
154 client_public,
155 EC_KEY_get0_public_key(server_key),
156 shared_secret,
157 hash, &hashlen)) != 0)
158 goto out;
159
160 /* save session id := H */
161 if (kex->session_id == NULL) {
162 kex->session_id_len = hashlen;
163 kex->session_id = malloc(kex->session_id_len);
164 if (kex->session_id == NULL) {
165 r = SSH_ERR_ALLOC_FAIL;
166 goto out;
167 }
168 memcpy(kex->session_id, hash, kex->session_id_len);
169 }
170
171 /* sign H */
172 if ((r = kex->sign(server_host_private, server_host_public, &signature,
173 &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0)
174 goto out;
175
176 /* destroy_sensitive_data(); */
177
178 public_key = EC_KEY_get0_public_key(server_key);
179 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
180 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
181 (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
182 (r = sshpkt_put_ec(ssh, public_key, group)) != 0 ||
183 (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
184 (r = sshpkt_send(ssh)) != 0)
185 goto out;
186
187 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
188 r = kex_send_newkeys(ssh);
189 out:
190 explicit_bzero(hash, sizeof(hash));
191 if (kex->ec_client_key) {
192 EC_KEY_free(kex->ec_client_key);
193 kex->ec_client_key = NULL;
194 }
195 if (server_key)
196 EC_KEY_free(server_key);
197 if (kbuf) {
198 explicit_bzero(kbuf, klen);
199 free(kbuf);
200 }
201 if (shared_secret)
202 BN_clear_free(shared_secret);
203 free(server_host_key_blob);
204 free(signature);
205 return r;
206 }
207 #endif /* defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC) */
208
209