1 /* $OpenBSD: kexdh.c,v 1.32 2019/01/21 10:40:11 djm Exp $ */
2 /*
3 * Copyright (c) 2019 Markus Friedl. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26 #include "includes.h"
27
28 #ifdef WITH_OPENSSL
29
30 #include <sys/types.h>
31
32 #include <signal.h>
33 #include <stdio.h>
34 #include <string.h>
35
36 #include "openbsd-compat/openssl-compat.h"
37 #include <openssl/dh.h>
38
39 #include "sshkey.h"
40 #include "kex.h"
41 #include "sshbuf.h"
42 #include "digest.h"
43 #include "ssherr.h"
44 #include "dh.h"
45
46 int
kex_dh_keygen(struct kex * kex)47 kex_dh_keygen(struct kex *kex)
48 {
49 switch (kex->kex_type) {
50 case KEX_DH_GRP1_SHA1:
51 kex->dh = dh_new_group1();
52 break;
53 case KEX_DH_GRP14_SHA1:
54 case KEX_DH_GRP14_SHA256:
55 kex->dh = dh_new_group14();
56 break;
57 case KEX_DH_GRP16_SHA512:
58 kex->dh = dh_new_group16();
59 break;
60 case KEX_DH_GRP18_SHA512:
61 kex->dh = dh_new_group18();
62 break;
63 default:
64 return SSH_ERR_INVALID_ARGUMENT;
65 }
66 if (kex->dh == NULL)
67 return SSH_ERR_ALLOC_FAIL;
68 return (dh_gen_key(kex->dh, kex->we_need * 8));
69 }
70
71 int
kex_dh_compute_key(struct kex * kex,BIGNUM * dh_pub,struct sshbuf * out)72 kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
73 {
74 BIGNUM *shared_secret = NULL;
75 u_char *kbuf = NULL;
76 size_t klen = 0;
77 int kout, r;
78
79 #ifdef DEBUG_KEXDH
80 fprintf(stderr, "dh_pub= ");
81 BN_print_fp(stderr, dh_pub);
82 fprintf(stderr, "\n");
83 debug("bits %d", BN_num_bits(dh_pub));
84 DHparams_print_fp(stderr, kex->dh);
85 fprintf(stderr, "\n");
86 #endif
87
88 if (!dh_pub_is_valid(kex->dh, dh_pub)) {
89 r = SSH_ERR_MESSAGE_INCOMPLETE;
90 goto out;
91 }
92 klen = DH_size(kex->dh);
93 if ((kbuf = malloc(klen)) == NULL ||
94 (shared_secret = BN_new()) == NULL) {
95 r = SSH_ERR_ALLOC_FAIL;
96 goto out;
97 }
98 if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 ||
99 BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
100 r = SSH_ERR_LIBCRYPTO_ERROR;
101 goto out;
102 }
103 #ifdef DEBUG_KEXDH
104 dump_digest("shared secret", kbuf, kout);
105 #endif
106 r = sshbuf_put_bignum2(out, shared_secret);
107 out:
108 freezero(kbuf, klen);
109 BN_clear_free(shared_secret);
110 return r;
111 }
112
113 int
kex_dh_keypair(struct kex * kex)114 kex_dh_keypair(struct kex *kex)
115 {
116 const BIGNUM *pub_key;
117 struct sshbuf *buf = NULL;
118 int r;
119
120 if ((r = kex_dh_keygen(kex)) != 0)
121 return r;
122 DH_get0_key(kex->dh, &pub_key, NULL);
123 if ((buf = sshbuf_new()) == NULL)
124 return SSH_ERR_ALLOC_FAIL;
125 if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
126 (r = sshbuf_get_u32(buf, NULL)) != 0)
127 goto out;
128 #ifdef DEBUG_KEXDH
129 DHparams_print_fp(stderr, kex->dh);
130 fprintf(stderr, "pub= ");
131 BN_print_fp(stderr, pub_key);
132 fprintf(stderr, "\n");
133 #endif
134 kex->client_pub = buf;
135 buf = NULL;
136 out:
137 sshbuf_free(buf);
138 return r;
139 }
140
141 int
kex_dh_enc(struct kex * kex,const struct sshbuf * client_blob,struct sshbuf ** server_blobp,struct sshbuf ** shared_secretp)142 kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
143 struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
144 {
145 const BIGNUM *pub_key;
146 struct sshbuf *server_blob = NULL;
147 int r;
148
149 *server_blobp = NULL;
150 *shared_secretp = NULL;
151
152 if ((r = kex_dh_keygen(kex)) != 0)
153 goto out;
154 DH_get0_key(kex->dh, &pub_key, NULL);
155 if ((server_blob = sshbuf_new()) == NULL) {
156 r = SSH_ERR_ALLOC_FAIL;
157 goto out;
158 }
159 if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
160 (r = sshbuf_get_u32(server_blob, NULL)) != 0)
161 goto out;
162 if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
163 goto out;
164 *server_blobp = server_blob;
165 server_blob = NULL;
166 out:
167 DH_free(kex->dh);
168 kex->dh = NULL;
169 sshbuf_free(server_blob);
170 return r;
171 }
172
173 int
kex_dh_dec(struct kex * kex,const struct sshbuf * dh_blob,struct sshbuf ** shared_secretp)174 kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
175 struct sshbuf **shared_secretp)
176 {
177 struct sshbuf *buf = NULL;
178 BIGNUM *dh_pub = NULL;
179 int r;
180
181 *shared_secretp = NULL;
182
183 if ((buf = sshbuf_new()) == NULL) {
184 r = SSH_ERR_ALLOC_FAIL;
185 goto out;
186 }
187 if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
188 (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
189 goto out;
190 sshbuf_reset(buf);
191 if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
192 goto out;
193 *shared_secretp = buf;
194 buf = NULL;
195 out:
196 DH_free(kex->dh);
197 kex->dh = NULL;
198 sshbuf_free(buf);
199 return r;
200 }
201 #endif /* WITH_OPENSSL */
202