1/* $OpenBSD: kexecdh.c,v 1.10 2019/01/21 10:40:11 djm Exp $ */
2/*
3 * Copyright (c) 2010 Damien Miller.  All rights reserved.
4 * Copyright (c) 2019 Markus Friedl.  All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include "includes.h"
28
29#if defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC)
30
31#include <sys/types.h>
32
33#include <stdio.h>
34#include <string.h>
35#include <signal.h>
36
37#include <openssl/ecdh.h>
38
39#include "sshkey.h"
40#include "kex.h"
41#include "sshbuf.h"
42#include "digest.h"
43#include "ssherr.h"
44
45static int
46kex_ecdh_dec_key_group(struct kex *, const struct sshbuf *, EC_KEY *key,
47    const EC_GROUP *, struct sshbuf **);
48
49int
50kex_ecdh_keypair(struct kex *kex)
51{
52	EC_KEY *client_key = NULL;
53	const EC_GROUP *group;
54	const EC_POINT *public_key;
55	struct sshbuf *buf = NULL;
56	int r;
57
58	if ((client_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
59		r = SSH_ERR_ALLOC_FAIL;
60		goto out;
61	}
62	if (EC_KEY_generate_key(client_key) != 1) {
63		r = SSH_ERR_LIBCRYPTO_ERROR;
64		goto out;
65	}
66	group = EC_KEY_get0_group(client_key);
67	public_key = EC_KEY_get0_public_key(client_key);
68
69	if ((buf = sshbuf_new()) == NULL) {
70		r = SSH_ERR_ALLOC_FAIL;
71		goto out;
72	}
73	if ((r = sshbuf_put_ec(buf, public_key, group)) != 0 ||
74	    (r = sshbuf_get_u32(buf, NULL)) != 0)
75		goto out;
76#ifdef DEBUG_KEXECDH
77	fputs("client private key:\n", stderr);
78	sshkey_dump_ec_key(client_key);
79#endif
80	kex->ec_client_key = client_key;
81	kex->ec_group = group;
82	client_key = NULL;	/* owned by the kex */
83	kex->client_pub = buf;
84	buf = NULL;
85 out:
86	EC_KEY_free(client_key);
87	sshbuf_free(buf);
88	return r;
89}
90
91int
92kex_ecdh_enc(struct kex *kex, const struct sshbuf *client_blob,
93    struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
94{
95	const EC_GROUP *group;
96	const EC_POINT *pub_key;
97	EC_KEY *server_key = NULL;
98	struct sshbuf *server_blob = NULL;
99	int r;
100
101	*server_blobp = NULL;
102	*shared_secretp = NULL;
103
104	if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
105		r = SSH_ERR_ALLOC_FAIL;
106		goto out;
107	}
108	if (EC_KEY_generate_key(server_key) != 1) {
109		r = SSH_ERR_LIBCRYPTO_ERROR;
110		goto out;
111	}
112	group = EC_KEY_get0_group(server_key);
113
114#ifdef DEBUG_KEXECDH
115	fputs("server private key:\n", stderr);
116	sshkey_dump_ec_key(server_key);
117#endif
118	pub_key = EC_KEY_get0_public_key(server_key);
119	if ((server_blob = sshbuf_new()) == NULL) {
120		r = SSH_ERR_ALLOC_FAIL;
121		goto out;
122	}
123	if ((r = sshbuf_put_ec(server_blob, pub_key, group)) != 0 ||
124	    (r = sshbuf_get_u32(server_blob, NULL)) != 0)
125		goto out;
126	if ((r = kex_ecdh_dec_key_group(kex, client_blob, server_key, group,
127	    shared_secretp)) != 0)
128		goto out;
129	*server_blobp = server_blob;
130	server_blob = NULL;
131 out:
132	EC_KEY_free(server_key);
133	sshbuf_free(server_blob);
134	return r;
135}
136
137static int
138kex_ecdh_dec_key_group(struct kex *kex, const struct sshbuf *ec_blob,
139    EC_KEY *key, const EC_GROUP *group, struct sshbuf **shared_secretp)
140{
141	struct sshbuf *buf = NULL;
142	BIGNUM *shared_secret = NULL;
143	EC_POINT *dh_pub = NULL;
144	u_char *kbuf = NULL;
145	size_t klen = 0;
146	int r;
147
148	*shared_secretp = NULL;
149
150	if ((buf = sshbuf_new()) == NULL) {
151		r = SSH_ERR_ALLOC_FAIL;
152		goto out;
153	}
154	if ((r = sshbuf_put_stringb(buf, ec_blob)) != 0)
155		goto out;
156	if ((dh_pub = EC_POINT_new(group)) == NULL) {
157		r = SSH_ERR_ALLOC_FAIL;
158		goto out;
159	}
160	if ((r = sshbuf_get_ec(buf, dh_pub, group)) != 0) {
161		goto out;
162	}
163	sshbuf_reset(buf);
164
165#ifdef DEBUG_KEXECDH
166	fputs("public key:\n", stderr);
167	sshkey_dump_ec_point(group, dh_pub);
168#endif
169	if (sshkey_ec_validate_public(group, dh_pub) != 0) {
170		r = SSH_ERR_MESSAGE_INCOMPLETE;
171		goto out;
172	}
173	klen = (EC_GROUP_get_degree(group) + 7) / 8;
174	if ((kbuf = malloc(klen)) == NULL ||
175	    (shared_secret = BN_new()) == NULL) {
176		r = SSH_ERR_ALLOC_FAIL;
177		goto out;
178	}
179	if (ECDH_compute_key(kbuf, klen, dh_pub, key, NULL) != (int)klen ||
180	    BN_bin2bn(kbuf, klen, shared_secret) == NULL) {
181		r = SSH_ERR_LIBCRYPTO_ERROR;
182		goto out;
183	}
184#ifdef DEBUG_KEXECDH
185	dump_digest("shared secret", kbuf, klen);
186#endif
187	if ((r = sshbuf_put_bignum2(buf, shared_secret)) != 0)
188		goto out;
189	*shared_secretp = buf;
190	buf = NULL;
191 out:
192	EC_POINT_clear_free(dh_pub);
193	BN_clear_free(shared_secret);
194	freezero(kbuf, klen);
195	sshbuf_free(buf);
196	return r;
197}
198
199int
200kex_ecdh_dec(struct kex *kex, const struct sshbuf *server_blob,
201    struct sshbuf **shared_secretp)
202{
203	int r;
204
205	r = kex_ecdh_dec_key_group(kex, server_blob, kex->ec_client_key,
206	    kex->ec_group, shared_secretp);
207	EC_KEY_free(kex->ec_client_key);
208	kex->ec_client_key = NULL;
209	return r;
210}
211
212#else
213
214#include "ssherr.h"
215
216struct kex;
217struct sshbuf;
218struct sshkey;
219
220int
221kex_ecdh_keypair(struct kex *kex)
222{
223	return SSH_ERR_SIGN_ALG_UNSUPPORTED;
224}
225
226int
227kex_ecdh_enc(struct kex *kex, const struct sshbuf *client_blob,
228    struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
229{
230	return SSH_ERR_SIGN_ALG_UNSUPPORTED;
231}
232
233int
234kex_ecdh_dec(struct kex *kex, const struct sshbuf *server_blob,
235    struct sshbuf **shared_secretp)
236{
237	return SSH_ERR_SIGN_ALG_UNSUPPORTED;
238}
239#endif /* defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC) */
240