1 /* $NetBSD: kexecdh.c,v 1.8 2019/04/20 17:16:40 christos Exp $ */
2 /* $OpenBSD: kexecdh.c,v 1.10 2019/01/21 10:40:11 djm Exp $ */
3 /*
4 * Copyright (c) 2010 Damien Miller. All rights reserved.
5 * Copyright (c) 2019 Markus Friedl. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #include "includes.h"
29 __RCSID("$NetBSD: kexecdh.c,v 1.8 2019/04/20 17:16:40 christos Exp $");
30 #include <sys/types.h>
31
32 #include <stdio.h>
33 #include <string.h>
34 #include <signal.h>
35
36 #include <openssl/ecdh.h>
37
38 #include "sshkey.h"
39 #include "kex.h"
40 #include "sshbuf.h"
41 #include "digest.h"
42 #include "ssherr.h"
43
44 static int
45 kex_ecdh_dec_key_group(struct kex *, const struct sshbuf *, EC_KEY *key,
46 const EC_GROUP *, struct sshbuf **);
47
48 int
kex_ecdh_keypair(struct kex * kex)49 kex_ecdh_keypair(struct kex *kex)
50 {
51 EC_KEY *client_key = NULL;
52 const EC_GROUP *group;
53 const EC_POINT *public_key;
54 struct sshbuf *buf = NULL;
55 int r;
56
57 if ((client_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
58 r = SSH_ERR_ALLOC_FAIL;
59 goto out;
60 }
61 if (EC_KEY_generate_key(client_key) != 1) {
62 r = SSH_ERR_LIBCRYPTO_ERROR;
63 goto out;
64 }
65 group = EC_KEY_get0_group(client_key);
66 public_key = EC_KEY_get0_public_key(client_key);
67
68 if ((buf = sshbuf_new()) == NULL) {
69 r = SSH_ERR_ALLOC_FAIL;
70 goto out;
71 }
72 if ((r = sshbuf_put_ec(buf, public_key, group)) != 0 ||
73 (r = sshbuf_get_u32(buf, NULL)) != 0)
74 goto out;
75 #ifdef DEBUG_KEXECDH
76 fputs("client private key:\n", stderr);
77 sshkey_dump_ec_key(client_key);
78 #endif
79 kex->ec_client_key = client_key;
80 kex->ec_group = group;
81 client_key = NULL; /* owned by the kex */
82 kex->client_pub = buf;
83 buf = NULL;
84 out:
85 EC_KEY_free(client_key);
86 sshbuf_free(buf);
87 return r;
88 }
89
90 int
kex_ecdh_enc(struct kex * kex,const struct sshbuf * client_blob,struct sshbuf ** server_blobp,struct sshbuf ** shared_secretp)91 kex_ecdh_enc(struct kex *kex, const struct sshbuf *client_blob,
92 struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
93 {
94 const EC_GROUP *group;
95 const EC_POINT *pub_key;
96 EC_KEY *server_key = NULL;
97 struct sshbuf *server_blob = NULL;
98 int r;
99
100 *server_blobp = NULL;
101 *shared_secretp = NULL;
102
103 if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
104 r = SSH_ERR_ALLOC_FAIL;
105 goto out;
106 }
107 if (EC_KEY_generate_key(server_key) != 1) {
108 r = SSH_ERR_LIBCRYPTO_ERROR;
109 goto out;
110 }
111 group = EC_KEY_get0_group(server_key);
112
113 #ifdef DEBUG_KEXECDH
114 fputs("server private key:\n", stderr);
115 sshkey_dump_ec_key(server_key);
116 #endif
117 pub_key = EC_KEY_get0_public_key(server_key);
118 if ((server_blob = sshbuf_new()) == NULL) {
119 r = SSH_ERR_ALLOC_FAIL;
120 goto out;
121 }
122 if ((r = sshbuf_put_ec(server_blob, pub_key, group)) != 0 ||
123 (r = sshbuf_get_u32(server_blob, NULL)) != 0)
124 goto out;
125 if ((r = kex_ecdh_dec_key_group(kex, client_blob, server_key, group,
126 shared_secretp)) != 0)
127 goto out;
128 *server_blobp = server_blob;
129 server_blob = NULL;
130 out:
131 EC_KEY_free(server_key);
132 sshbuf_free(server_blob);
133 return r;
134 }
135
136 static int
kex_ecdh_dec_key_group(struct kex * kex,const struct sshbuf * ec_blob,EC_KEY * key,const EC_GROUP * group,struct sshbuf ** shared_secretp)137 kex_ecdh_dec_key_group(struct kex *kex, const struct sshbuf *ec_blob,
138 EC_KEY *key, const EC_GROUP *group, struct sshbuf **shared_secretp)
139 {
140 struct sshbuf *buf = NULL;
141 BIGNUM *shared_secret = NULL;
142 EC_POINT *dh_pub = NULL;
143 u_char *kbuf = NULL;
144 size_t klen = 0;
145 int r;
146
147 *shared_secretp = NULL;
148
149 if ((buf = sshbuf_new()) == NULL) {
150 r = SSH_ERR_ALLOC_FAIL;
151 goto out;
152 }
153 if ((r = sshbuf_put_stringb(buf, ec_blob)) != 0)
154 goto out;
155 if ((dh_pub = EC_POINT_new(group)) == NULL) {
156 r = SSH_ERR_ALLOC_FAIL;
157 goto out;
158 }
159 if ((r = sshbuf_get_ec(buf, dh_pub, group)) != 0) {
160 goto out;
161 }
162 sshbuf_reset(buf);
163
164 #ifdef DEBUG_KEXECDH
165 fputs("public key:\n", stderr);
166 sshkey_dump_ec_point(group, dh_pub);
167 #endif
168 if (sshkey_ec_validate_public(group, dh_pub) != 0) {
169 r = SSH_ERR_MESSAGE_INCOMPLETE;
170 goto out;
171 }
172 klen = (EC_GROUP_get_degree(group) + 7) / 8;
173 if ((kbuf = malloc(klen)) == NULL ||
174 (shared_secret = BN_new()) == NULL) {
175 r = SSH_ERR_ALLOC_FAIL;
176 goto out;
177 }
178 if (ECDH_compute_key(kbuf, klen, dh_pub, key, NULL) != (int)klen ||
179 BN_bin2bn(kbuf, klen, shared_secret) == NULL) {
180 r = SSH_ERR_LIBCRYPTO_ERROR;
181 goto out;
182 }
183 #ifdef DEBUG_KEXECDH
184 dump_digest("shared secret", kbuf, klen);
185 #endif
186 if ((r = sshbuf_put_bignum2(buf, shared_secret)) != 0)
187 goto out;
188 *shared_secretp = buf;
189 buf = NULL;
190 out:
191 EC_POINT_clear_free(dh_pub);
192 BN_clear_free(shared_secret);
193 freezero(kbuf, klen);
194 sshbuf_free(buf);
195 return r;
196 }
197
198 int
kex_ecdh_dec(struct kex * kex,const struct sshbuf * server_blob,struct sshbuf ** shared_secretp)199 kex_ecdh_dec(struct kex *kex, const struct sshbuf *server_blob,
200 struct sshbuf **shared_secretp)
201 {
202 int r;
203
204 r = kex_ecdh_dec_key_group(kex, server_blob, kex->ec_client_key,
205 kex->ec_group, shared_secretp);
206 EC_KEY_free(kex->ec_client_key);
207 kex->ec_client_key = NULL;
208 return r;
209 }
210