xref: /openssh-portable/kexdh.c (revision 3b98b6e2)
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 <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 #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