xref: /netbsd-src/crypto/external/bsd/openssh/dist/kexdh.c (revision 17418e98f281f84e3d22de9717222f9c2ee84d3a)
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