1 /* $OpenBSD: kexdh.c,v 1.34 2020/12/04 02:29:25 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 <stdio.h>
33 #include <string.h>
34 #include <signal.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 #include "log.h"
46
47 int
kex_dh_keygen(struct kex * kex)48 kex_dh_keygen(struct kex *kex)
49 {
50 switch (kex->kex_type) {
51 case KEX_DH_GRP1_SHA1:
52 kex->dh = dh_new_group1();
53 break;
54 case KEX_DH_GRP14_SHA1:
55 case KEX_DH_GRP14_SHA256:
56 kex->dh = dh_new_group14();
57 break;
58 case KEX_DH_GRP16_SHA512:
59 kex->dh = dh_new_group16();
60 break;
61 case KEX_DH_GRP18_SHA512:
62 kex->dh = dh_new_group18();
63 break;
64 default:
65 return SSH_ERR_INVALID_ARGUMENT;
66 }
67 if (kex->dh == NULL)
68 return SSH_ERR_ALLOC_FAIL;
69 return (dh_gen_key(kex->dh, kex->we_need * 8));
70 }
71
72 int
kex_dh_compute_key(struct kex * kex,BIGNUM * dh_pub,struct sshbuf * out)73 kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
74 {
75 BIGNUM *shared_secret = NULL;
76 u_char *kbuf = NULL;
77 size_t klen = 0;
78 int kout, r;
79
80 #ifdef DEBUG_KEXDH
81 fprintf(stderr, "dh_pub= ");
82 BN_print_fp(stderr, dh_pub);
83 fprintf(stderr, "\n");
84 debug("bits %d", BN_num_bits(dh_pub));
85 DHparams_print_fp(stderr, kex->dh);
86 fprintf(stderr, "\n");
87 #endif
88
89 if (!dh_pub_is_valid(kex->dh, dh_pub)) {
90 r = SSH_ERR_MESSAGE_INCOMPLETE;
91 goto out;
92 }
93 klen = DH_size(kex->dh);
94 if ((kbuf = malloc(klen)) == NULL ||
95 (shared_secret = BN_new()) == NULL) {
96 r = SSH_ERR_ALLOC_FAIL;
97 goto out;
98 }
99 if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 ||
100 BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
101 r = SSH_ERR_LIBCRYPTO_ERROR;
102 goto out;
103 }
104 #ifdef DEBUG_KEXDH
105 dump_digest("shared secret", kbuf, kout);
106 #endif
107 r = sshbuf_put_bignum2(out, shared_secret);
108 out:
109 freezero(kbuf, klen);
110 BN_clear_free(shared_secret);
111 return r;
112 }
113
114 int
kex_dh_keypair(struct kex * kex)115 kex_dh_keypair(struct kex *kex)
116 {
117 const BIGNUM *pub_key;
118 struct sshbuf *buf = NULL;
119 int r;
120
121 if ((r = kex_dh_keygen(kex)) != 0)
122 return r;
123 DH_get0_key(kex->dh, &pub_key, NULL);
124 if ((buf = sshbuf_new()) == NULL)
125 return SSH_ERR_ALLOC_FAIL;
126 if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
127 (r = sshbuf_get_u32(buf, NULL)) != 0)
128 goto out;
129 #ifdef DEBUG_KEXDH
130 DHparams_print_fp(stderr, kex->dh);
131 fprintf(stderr, "pub= ");
132 BN_print_fp(stderr, pub_key);
133 fprintf(stderr, "\n");
134 #endif
135 kex->client_pub = buf;
136 buf = NULL;
137 out:
138 sshbuf_free(buf);
139 return r;
140 }
141
142 int
kex_dh_enc(struct kex * kex,const struct sshbuf * client_blob,struct sshbuf ** server_blobp,struct sshbuf ** shared_secretp)143 kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
144 struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
145 {
146 const BIGNUM *pub_key;
147 struct sshbuf *server_blob = NULL;
148 int r;
149
150 *server_blobp = NULL;
151 *shared_secretp = NULL;
152
153 if ((r = kex_dh_keygen(kex)) != 0)
154 goto out;
155 DH_get0_key(kex->dh, &pub_key, NULL);
156 if ((server_blob = sshbuf_new()) == NULL) {
157 r = SSH_ERR_ALLOC_FAIL;
158 goto out;
159 }
160 if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
161 (r = sshbuf_get_u32(server_blob, NULL)) != 0)
162 goto out;
163 if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
164 goto out;
165 *server_blobp = server_blob;
166 server_blob = NULL;
167 out:
168 DH_free(kex->dh);
169 kex->dh = NULL;
170 sshbuf_free(server_blob);
171 return r;
172 }
173
174 int
kex_dh_dec(struct kex * kex,const struct sshbuf * dh_blob,struct sshbuf ** shared_secretp)175 kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
176 struct sshbuf **shared_secretp)
177 {
178 struct sshbuf *buf = NULL;
179 BIGNUM *dh_pub = NULL;
180 int r;
181
182 *shared_secretp = NULL;
183
184 if ((buf = sshbuf_new()) == NULL) {
185 r = SSH_ERR_ALLOC_FAIL;
186 goto out;
187 }
188 if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
189 (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
190 goto out;
191 sshbuf_reset(buf);
192 if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
193 goto out;
194 *shared_secretp = buf;
195 buf = NULL;
196 out:
197 BN_free(dh_pub);
198 DH_free(kex->dh);
199 kex->dh = NULL;
200 sshbuf_free(buf);
201 return r;
202 }
203 #endif /* WITH_OPENSSL */
204