1 /* $NetBSD: kexdh.c,v 1.10 2021/03/05 17:47:16 christos Exp $ */
2 /* $OpenBSD: kexdh.c,v 1.34 2020/12/04 02:29:25 djm Exp $ */
3
4 /*
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: kexdh.c,v 1.10 2021/03/05 17:47:16 christos Exp $");
30 #include <sys/types.h>
31
32 #include <stdio.h>
33 #include <string.h>
34 #include <signal.h>
35
36 #include "sshkey.h"
37 #include "kex.h"
38 #include "sshbuf.h"
39 #include "digest.h"
40 #include "ssherr.h"
41 #include "dh.h"
42 #include "log.h"
43
44 int
kex_dh_keygen(struct kex * kex)45 kex_dh_keygen(struct kex *kex)
46 {
47 switch (kex->kex_type) {
48 case KEX_DH_GRP1_SHA1:
49 kex->dh = dh_new_group1();
50 break;
51 case KEX_DH_GRP14_SHA1:
52 case KEX_DH_GRP14_SHA256:
53 kex->dh = dh_new_group14();
54 break;
55 case KEX_DH_GRP16_SHA512:
56 kex->dh = dh_new_group16();
57 break;
58 case KEX_DH_GRP18_SHA512:
59 kex->dh = dh_new_group18();
60 break;
61 default:
62 return SSH_ERR_INVALID_ARGUMENT;
63 }
64 if (kex->dh == NULL)
65 return SSH_ERR_ALLOC_FAIL;
66 return (dh_gen_key(kex->dh, kex->we_need * 8));
67 }
68
69 int
kex_dh_compute_key(struct kex * kex,BIGNUM * dh_pub,struct sshbuf * out)70 kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
71 {
72 BIGNUM *shared_secret = NULL;
73 u_char *kbuf = NULL;
74 size_t klen = 0;
75 int kout, r;
76
77 #ifdef DEBUG_KEXDH
78 fprintf(stderr, "dh_pub= ");
79 BN_print_fp(stderr, dh_pub);
80 fprintf(stderr, "\n");
81 debug("bits %d", BN_num_bits(dh_pub));
82 DHparams_print_fp(stderr, kex->dh);
83 fprintf(stderr, "\n");
84 #endif
85
86 if (!dh_pub_is_valid(kex->dh, dh_pub)) {
87 r = SSH_ERR_MESSAGE_INCOMPLETE;
88 goto out;
89 }
90 klen = DH_size(kex->dh);
91 if ((kbuf = malloc(klen)) == NULL ||
92 (shared_secret = BN_new()) == NULL) {
93 r = SSH_ERR_ALLOC_FAIL;
94 goto out;
95 }
96 if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 ||
97 BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
98 r = SSH_ERR_LIBCRYPTO_ERROR;
99 goto out;
100 }
101 #ifdef DEBUG_KEXDH
102 dump_digest("shared secret", kbuf, kout);
103 #endif
104 r = sshbuf_put_bignum2(out, shared_secret);
105 out:
106 freezero(kbuf, klen);
107 BN_clear_free(shared_secret);
108 return r;
109 }
110
111 int
kex_dh_keypair(struct kex * kex)112 kex_dh_keypair(struct kex *kex)
113 {
114 const BIGNUM *pub_key;
115 struct sshbuf *buf = NULL;
116 int r;
117
118 if ((r = kex_dh_keygen(kex)) != 0)
119 return r;
120 DH_get0_key(kex->dh, &pub_key, NULL);
121 if ((buf = sshbuf_new()) == NULL)
122 return SSH_ERR_ALLOC_FAIL;
123 if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
124 (r = sshbuf_get_u32(buf, NULL)) != 0)
125 goto out;
126 #ifdef DEBUG_KEXDH
127 DHparams_print_fp(stderr, kex->dh);
128 fprintf(stderr, "pub= ");
129 BN_print_fp(stderr, pub_key);
130 fprintf(stderr, "\n");
131 #endif
132 kex->client_pub = buf;
133 buf = NULL;
134 out:
135 sshbuf_free(buf);
136 return r;
137 }
138
139 int
kex_dh_enc(struct kex * kex,const struct sshbuf * client_blob,struct sshbuf ** server_blobp,struct sshbuf ** shared_secretp)140 kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
141 struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
142 {
143 const BIGNUM *pub_key;
144 struct sshbuf *server_blob = NULL;
145 int r;
146
147 *server_blobp = NULL;
148 *shared_secretp = NULL;
149
150 if ((r = kex_dh_keygen(kex)) != 0)
151 goto out;
152 DH_get0_key(kex->dh, &pub_key, NULL);
153 if ((server_blob = sshbuf_new()) == NULL) {
154 r = SSH_ERR_ALLOC_FAIL;
155 goto out;
156 }
157 if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
158 (r = sshbuf_get_u32(server_blob, NULL)) != 0)
159 goto out;
160 if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
161 goto out;
162 *server_blobp = server_blob;
163 server_blob = NULL;
164 out:
165 DH_free(kex->dh);
166 kex->dh = NULL;
167 sshbuf_free(server_blob);
168 return r;
169 }
170
171 int
kex_dh_dec(struct kex * kex,const struct sshbuf * dh_blob,struct sshbuf ** shared_secretp)172 kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
173 struct sshbuf **shared_secretp)
174 {
175 struct sshbuf *buf = NULL;
176 BIGNUM *dh_pub = NULL;
177 int r;
178
179 *shared_secretp = NULL;
180
181 if ((buf = sshbuf_new()) == NULL) {
182 r = SSH_ERR_ALLOC_FAIL;
183 goto out;
184 }
185 if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
186 (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
187 goto out;
188 sshbuf_reset(buf);
189 if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
190 goto out;
191 *shared_secretp = buf;
192 buf = NULL;
193 out:
194 BN_free(dh_pub);
195 DH_free(kex->dh);
196 kex->dh = NULL;
197 sshbuf_free(buf);
198 return r;
199 }
200