1 /* $OpenBSD: kexc25519s.c,v 1.10 2015/12/04 16:41:28 markus Exp $ */
2 /*
3 * Copyright (c) 2001 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 * 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 #include <sys/types.h>
30 #include <stdio.h>
31 #include <string.h>
32 #include <signal.h>
33
34 #include "sshkey.h"
35 #include "cipher.h"
36 #include "digest.h"
37 #include "kex.h"
38 #include "log.h"
39 #include "packet.h"
40 #include "ssh2.h"
41 #include "sshbuf.h"
42 #include "ssherr.h"
43
44 static int input_kex_c25519_init(int, u_int32_t, void *);
45
46 int
kexc25519_server(struct ssh * ssh)47 kexc25519_server(struct ssh *ssh)
48 {
49 debug("expecting SSH2_MSG_KEX_ECDH_INIT");
50 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_c25519_init);
51 return 0;
52 }
53
54 static int
input_kex_c25519_init(int type,u_int32_t seq,void * ctxt)55 input_kex_c25519_init(int type, u_int32_t seq, void *ctxt)
56 {
57 struct ssh *ssh = ctxt;
58 struct kex *kex = ssh->kex;
59 struct sshkey *server_host_private, *server_host_public;
60 struct sshbuf *shared_secret = NULL;
61 u_char *server_host_key_blob = NULL, *signature = NULL;
62 u_char server_key[CURVE25519_SIZE];
63 u_char *client_pubkey = NULL;
64 u_char server_pubkey[CURVE25519_SIZE];
65 u_char hash[SSH_DIGEST_MAX_LENGTH];
66 size_t slen, pklen, sbloblen, hashlen;
67 int r;
68
69 /* generate private key */
70 kexc25519_keygen(server_key, server_pubkey);
71 #ifdef DEBUG_KEXECDH
72 dump_digest("server private key:", server_key, sizeof(server_key));
73 #endif
74 if (kex->load_host_public_key == NULL ||
75 kex->load_host_private_key == NULL) {
76 r = SSH_ERR_INVALID_ARGUMENT;
77 goto out;
78 }
79 server_host_public = kex->load_host_public_key(kex->hostkey_type,
80 kex->hostkey_nid, ssh);
81 server_host_private = kex->load_host_private_key(kex->hostkey_type,
82 kex->hostkey_nid, ssh);
83 if (server_host_public == NULL) {
84 r = SSH_ERR_NO_HOSTKEY_LOADED;
85 goto out;
86 }
87
88 if ((r = sshpkt_get_string(ssh, &client_pubkey, &pklen)) != 0 ||
89 (r = sshpkt_get_end(ssh)) != 0)
90 goto out;
91 if (pklen != CURVE25519_SIZE) {
92 r = SSH_ERR_SIGNATURE_INVALID;
93 goto out;
94 }
95 #ifdef DEBUG_KEXECDH
96 dump_digest("client public key:", client_pubkey, CURVE25519_SIZE);
97 #endif
98
99 if ((shared_secret = sshbuf_new()) == NULL) {
100 r = SSH_ERR_ALLOC_FAIL;
101 goto out;
102 }
103 if ((r = kexc25519_shared_key(server_key, client_pubkey,
104 shared_secret)) < 0)
105 goto out;
106
107 /* calc H */
108 if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
109 &sbloblen)) != 0)
110 goto out;
111 hashlen = sizeof(hash);
112 if ((r = kex_c25519_hash(
113 kex->hash_alg,
114 kex->client_version_string,
115 kex->server_version_string,
116 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
117 sshbuf_ptr(kex->my), sshbuf_len(kex->my),
118 server_host_key_blob, sbloblen,
119 client_pubkey,
120 server_pubkey,
121 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
122 hash, &hashlen)) < 0)
123 goto out;
124
125 /* save session id := H */
126 if (kex->session_id == NULL) {
127 kex->session_id_len = hashlen;
128 kex->session_id = malloc(kex->session_id_len);
129 if (kex->session_id == NULL) {
130 r = SSH_ERR_ALLOC_FAIL;
131 goto out;
132 }
133 memcpy(kex->session_id, hash, kex->session_id_len);
134 }
135
136 /* sign H */
137 if ((r = kex->sign(server_host_private, server_host_public, &signature,
138 &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0)
139 goto out;
140
141 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
142 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
143 (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
144 (r = sshpkt_put_string(ssh, server_pubkey, sizeof(server_pubkey))) != 0 ||
145 (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
146 (r = sshpkt_send(ssh)) != 0)
147 goto out;
148
149 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
150 r = kex_send_newkeys(ssh);
151 out:
152 explicit_bzero(hash, sizeof(hash));
153 explicit_bzero(server_key, sizeof(server_key));
154 free(server_host_key_blob);
155 free(signature);
156 free(client_pubkey);
157 sshbuf_free(shared_secret);
158 return r;
159 }
160