1 /* $OpenBSD: kexc25519.c,v 1.8 2015/01/19 20:16:15 markus Exp $ */
2 /*
3 * Copyright (c) 2001, 2013 Markus Friedl. All rights reserved.
4 * Copyright (c) 2010 Damien Miller. All rights reserved.
5 * Copyright (c) 2013 Aris Adamantiadis. 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
30 #include <sys/types.h>
31
32 #include <signal.h>
33 #include <string.h>
34
35 #include <openssl/bn.h>
36 #include <openssl/evp.h>
37
38 #include "sshbuf.h"
39 #include "ssh2.h"
40 #include "sshkey.h"
41 #include "cipher.h"
42 #include "kex.h"
43 #include "log.h"
44 #include "digest.h"
45 #include "ssherr.h"
46
47 extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE],
48 const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE])
49 __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
50 __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)))
51 __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE)));
52
53 void
kexc25519_keygen(u_char key[CURVE25519_SIZE],u_char pub[CURVE25519_SIZE])54 kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
55 {
56 static const u_char basepoint[CURVE25519_SIZE] = {9};
57
58 arc4random_buf(key, CURVE25519_SIZE);
59 crypto_scalarmult_curve25519(pub, key, basepoint);
60 }
61
62 int
kexc25519_shared_key(const u_char key[CURVE25519_SIZE],const u_char pub[CURVE25519_SIZE],struct sshbuf * out)63 kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
64 const u_char pub[CURVE25519_SIZE], struct sshbuf *out)
65 {
66 u_char shared_key[CURVE25519_SIZE];
67 int r;
68
69 crypto_scalarmult_curve25519(shared_key, key, pub);
70 #ifdef DEBUG_KEXECDH
71 dump_digest("shared secret", shared_key, CURVE25519_SIZE);
72 #endif
73 sshbuf_reset(out);
74 r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE);
75 explicit_bzero(shared_key, CURVE25519_SIZE);
76 return r;
77 }
78
79 int
kex_c25519_hash(int hash_alg,const char * client_version_string,const char * server_version_string,const char * ckexinit,size_t ckexinitlen,const char * skexinit,size_t skexinitlen,const u_char * serverhostkeyblob,size_t sbloblen,const u_char client_dh_pub[CURVE25519_SIZE],const u_char server_dh_pub[CURVE25519_SIZE],const u_char * shared_secret,size_t secretlen,u_char * hash,size_t * hashlen)80 kex_c25519_hash(
81 int hash_alg,
82 const char *client_version_string,
83 const char *server_version_string,
84 const char *ckexinit, size_t ckexinitlen,
85 const char *skexinit, size_t skexinitlen,
86 const u_char *serverhostkeyblob, size_t sbloblen,
87 const u_char client_dh_pub[CURVE25519_SIZE],
88 const u_char server_dh_pub[CURVE25519_SIZE],
89 const u_char *shared_secret, size_t secretlen,
90 u_char *hash, size_t *hashlen)
91 {
92 struct sshbuf *b;
93 int r;
94
95 if (*hashlen < ssh_digest_bytes(hash_alg))
96 return SSH_ERR_INVALID_ARGUMENT;
97 if ((b = sshbuf_new()) == NULL)
98 return SSH_ERR_ALLOC_FAIL;
99 if ((r = sshbuf_put_cstring(b, client_version_string)) < 0 ||
100 (r = sshbuf_put_cstring(b, server_version_string)) < 0 ||
101 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
102 (r = sshbuf_put_u32(b, ckexinitlen+1)) < 0 ||
103 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
104 (r = sshbuf_put(b, ckexinit, ckexinitlen)) < 0 ||
105 (r = sshbuf_put_u32(b, skexinitlen+1)) < 0 ||
106 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
107 (r = sshbuf_put(b, skexinit, skexinitlen)) < 0 ||
108 (r = sshbuf_put_string(b, serverhostkeyblob, sbloblen)) < 0 ||
109 (r = sshbuf_put_string(b, client_dh_pub, CURVE25519_SIZE)) < 0 ||
110 (r = sshbuf_put_string(b, server_dh_pub, CURVE25519_SIZE)) < 0 ||
111 (r = sshbuf_put(b, shared_secret, secretlen)) < 0) {
112 sshbuf_free(b);
113 return r;
114 }
115 #ifdef DEBUG_KEX
116 sshbuf_dump(b, stderr);
117 #endif
118 if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) {
119 sshbuf_free(b);
120 return SSH_ERR_LIBCRYPTO_ERROR;
121 }
122 sshbuf_free(b);
123 *hashlen = ssh_digest_bytes(hash_alg);
124 #ifdef DEBUG_KEX
125 dump_digest("hash", hash, *hashlen);
126 #endif
127 return 0;
128 }
129