1 /* $OpenBSD: kexc25519.c,v 1.17 2019/01/21 10:40:11 djm Exp $ */
3 * Copyright (c) 2019 Markus Friedl. All rights reserved.
4 * Copyright (c) 2010 Damien Miller. All rights reserved.
5 * Copyright (c) 2013 Aris Adamantiadis. All rights reserved.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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.
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.
30 #include <sys/types.h>
43 extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE],
44 const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE])
45 __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
46 __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)))
47 __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE)));
50 kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
52 static const u_char basepoint[CURVE25519_SIZE] = {9};
54 arc4random_buf(key, CURVE25519_SIZE);
55 crypto_scalarmult_curve25519(pub, key, basepoint);
59 kexc25519_shared_key_ext(const u_char key[CURVE25519_SIZE],
60 const u_char pub[CURVE25519_SIZE], struct sshbuf *out, int raw)
62 u_char shared_key[CURVE25519_SIZE];
63 u_char zero[CURVE25519_SIZE];
66 crypto_scalarmult_curve25519(shared_key, key, pub);
68 /* Check for all-zero shared secret */
69 explicit_bzero(zero, CURVE25519_SIZE);
70 if (timingsafe_bcmp(zero, shared_key, CURVE25519_SIZE) == 0)
71 return SSH_ERR_KEY_INVALID_EC_VALUE;
74 dump_digest("shared secret", shared_key, CURVE25519_SIZE);
77 r = sshbuf_put(out, shared_key, CURVE25519_SIZE);
79 r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE);
80 explicit_bzero(shared_key, CURVE25519_SIZE);
85 kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
86 const u_char pub[CURVE25519_SIZE], struct sshbuf *out)
88 return kexc25519_shared_key_ext(key, pub, out, 0);
92 kex_c25519_keypair(struct kex *kex)
94 struct sshbuf *buf = NULL;
98 if ((buf = sshbuf_new()) == NULL)
99 return SSH_ERR_ALLOC_FAIL;
100 if ((r = sshbuf_reserve(buf, CURVE25519_SIZE, &cp)) != 0)
102 kexc25519_keygen(kex->c25519_client_key, cp);
104 dump_digest("client public key c25519:", cp, CURVE25519_SIZE);
106 kex->client_pub = buf;
114 kex_c25519_enc(struct kex *kex, const struct sshbuf *client_blob,
115 struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
117 struct sshbuf *server_blob = NULL;
118 struct sshbuf *buf = NULL;
119 const u_char *client_pub;
121 u_char server_key[CURVE25519_SIZE];
124 *server_blobp = NULL;
125 *shared_secretp = NULL;
127 if (sshbuf_len(client_blob) != CURVE25519_SIZE) {
128 r = SSH_ERR_SIGNATURE_INVALID;
131 client_pub = sshbuf_ptr(client_blob);
133 dump_digest("client public key 25519:", client_pub, CURVE25519_SIZE);
135 /* allocate space for encrypted KEM key and ECDH pub key */
136 if ((server_blob = sshbuf_new()) == NULL) {
137 r = SSH_ERR_ALLOC_FAIL;
140 if ((r = sshbuf_reserve(server_blob, CURVE25519_SIZE, &server_pub)) != 0)
142 kexc25519_keygen(server_key, server_pub);
143 /* allocate shared secret */
144 if ((buf = sshbuf_new()) == NULL) {
145 r = SSH_ERR_ALLOC_FAIL;
148 if ((r = kexc25519_shared_key_ext(server_key, client_pub, buf, 0)) < 0)
151 dump_digest("server public key 25519:", server_pub, CURVE25519_SIZE);
152 dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
154 *server_blobp = server_blob;
155 *shared_secretp = buf;
159 explicit_bzero(server_key, sizeof(server_key));
160 sshbuf_free(server_blob);
166 kex_c25519_dec(struct kex *kex, const struct sshbuf *server_blob,
167 struct sshbuf **shared_secretp)
169 struct sshbuf *buf = NULL;
170 const u_char *server_pub;
173 *shared_secretp = NULL;
175 if (sshbuf_len(server_blob) != CURVE25519_SIZE) {
176 r = SSH_ERR_SIGNATURE_INVALID;
179 server_pub = sshbuf_ptr(server_blob);
181 dump_digest("server public key c25519:", server_pub, CURVE25519_SIZE);
184 if ((buf = sshbuf_new()) == NULL) {
185 r = SSH_ERR_ALLOC_FAIL;
188 if ((r = kexc25519_shared_key_ext(kex->c25519_client_key, server_pub,
192 dump_digest("encoded shared secret:", sshbuf_ptr(buf), sshbuf_len(buf));
194 *shared_secretp = buf;