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 <sys/types.h>
27
28 #include <stdio.h>
29 #include <string.h>
30 #include <signal.h>
31
32 #include "sshkey.h"
33 #include "kex.h"
34 #include "sshbuf.h"
35 #include "digest.h"
36 #include "ssherr.h"
37 #include "dh.h"
38 #include "log.h"
39
40 int
kex_dh_keygen(struct kex * kex)41 kex_dh_keygen(struct kex *kex)
42 {
43 switch (kex->kex_type) {
44 case KEX_DH_GRP1_SHA1:
45 kex->dh = dh_new_group1();
46 break;
47 case KEX_DH_GRP14_SHA1:
48 case KEX_DH_GRP14_SHA256:
49 kex->dh = dh_new_group14();
50 break;
51 case KEX_DH_GRP16_SHA512:
52 kex->dh = dh_new_group16();
53 break;
54 case KEX_DH_GRP18_SHA512:
55 kex->dh = dh_new_group18();
56 break;
57 default:
58 return SSH_ERR_INVALID_ARGUMENT;
59 }
60 if (kex->dh == NULL)
61 return SSH_ERR_ALLOC_FAIL;
62 return (dh_gen_key(kex->dh, kex->we_need * 8));
63 }
64
65 int
kex_dh_compute_key(struct kex * kex,BIGNUM * dh_pub,struct sshbuf * out)66 kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
67 {
68 BIGNUM *shared_secret = NULL;
69 u_char *kbuf = NULL;
70 size_t klen = 0;
71 int kout, r;
72
73 #ifdef DEBUG_KEXDH
74 fprintf(stderr, "dh_pub= ");
75 BN_print_fp(stderr, dh_pub);
76 fprintf(stderr, "\n");
77 debug("bits %d", BN_num_bits(dh_pub));
78 DHparams_print_fp(stderr, kex->dh);
79 fprintf(stderr, "\n");
80 #endif
81
82 if (!dh_pub_is_valid(kex->dh, dh_pub)) {
83 r = SSH_ERR_MESSAGE_INCOMPLETE;
84 goto out;
85 }
86 klen = DH_size(kex->dh);
87 if ((kbuf = malloc(klen)) == NULL ||
88 (shared_secret = BN_new()) == NULL) {
89 r = SSH_ERR_ALLOC_FAIL;
90 goto out;
91 }
92 if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 ||
93 BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
94 r = SSH_ERR_LIBCRYPTO_ERROR;
95 goto out;
96 }
97 #ifdef DEBUG_KEXDH
98 dump_digest("shared secret", kbuf, kout);
99 #endif
100 r = sshbuf_put_bignum2(out, shared_secret);
101 out:
102 freezero(kbuf, klen);
103 BN_clear_free(shared_secret);
104 return r;
105 }
106
107 int
kex_dh_keypair(struct kex * kex)108 kex_dh_keypair(struct kex *kex)
109 {
110 const BIGNUM *pub_key;
111 struct sshbuf *buf = NULL;
112 int r;
113
114 if ((r = kex_dh_keygen(kex)) != 0)
115 return r;
116 DH_get0_key(kex->dh, &pub_key, NULL);
117 if ((buf = sshbuf_new()) == NULL)
118 return SSH_ERR_ALLOC_FAIL;
119 if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
120 (r = sshbuf_get_u32(buf, NULL)) != 0)
121 goto out;
122 #ifdef DEBUG_KEXDH
123 DHparams_print_fp(stderr, kex->dh);
124 fprintf(stderr, "pub= ");
125 BN_print_fp(stderr, pub_key);
126 fprintf(stderr, "\n");
127 #endif
128 kex->client_pub = buf;
129 buf = NULL;
130 out:
131 sshbuf_free(buf);
132 return r;
133 }
134
135 int
kex_dh_enc(struct kex * kex,const struct sshbuf * client_blob,struct sshbuf ** server_blobp,struct sshbuf ** shared_secretp)136 kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
137 struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
138 {
139 const BIGNUM *pub_key;
140 struct sshbuf *server_blob = NULL;
141 int r;
142
143 *server_blobp = NULL;
144 *shared_secretp = NULL;
145
146 if ((r = kex_dh_keygen(kex)) != 0)
147 goto out;
148 DH_get0_key(kex->dh, &pub_key, NULL);
149 if ((server_blob = sshbuf_new()) == NULL) {
150 r = SSH_ERR_ALLOC_FAIL;
151 goto out;
152 }
153 if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
154 (r = sshbuf_get_u32(server_blob, NULL)) != 0)
155 goto out;
156 if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
157 goto out;
158 *server_blobp = server_blob;
159 server_blob = NULL;
160 out:
161 DH_free(kex->dh);
162 kex->dh = NULL;
163 sshbuf_free(server_blob);
164 return r;
165 }
166
167 int
kex_dh_dec(struct kex * kex,const struct sshbuf * dh_blob,struct sshbuf ** shared_secretp)168 kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
169 struct sshbuf **shared_secretp)
170 {
171 struct sshbuf *buf = NULL;
172 BIGNUM *dh_pub = NULL;
173 int r;
174
175 *shared_secretp = NULL;
176
177 if ((buf = sshbuf_new()) == NULL) {
178 r = SSH_ERR_ALLOC_FAIL;
179 goto out;
180 }
181 if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
182 (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
183 goto out;
184 sshbuf_reset(buf);
185 if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
186 goto out;
187 *shared_secretp = buf;
188 buf = NULL;
189 out:
190 BN_free(dh_pub);
191 DH_free(kex->dh);
192 kex->dh = NULL;
193 sshbuf_free(buf);
194 return r;
195 }
196