1/* $OpenBSD: kexc25519s.c,v 1.11 2017/05/31 04:19:28 djm 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
44static int input_kex_c25519_init(int, u_int32_t, struct ssh *);
45
46int
47kexc25519_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
54static int
55input_kex_c25519_init(int type, u_int32_t seq, struct ssh *ssh)
56{
57	struct kex *kex = ssh->kex;
58	struct sshkey *server_host_private, *server_host_public;
59	struct sshbuf *shared_secret = NULL;
60	u_char *server_host_key_blob = NULL, *signature = NULL;
61	u_char server_key[CURVE25519_SIZE];
62	u_char *client_pubkey = NULL;
63	u_char server_pubkey[CURVE25519_SIZE];
64	u_char hash[SSH_DIGEST_MAX_LENGTH];
65	size_t slen, pklen, sbloblen, hashlen;
66	int r;
67
68	/* generate private key */
69	kexc25519_keygen(server_key, server_pubkey);
70#ifdef DEBUG_KEXECDH
71	dump_digest("server private key:", server_key, sizeof(server_key));
72#endif
73	if (kex->load_host_public_key == NULL ||
74	    kex->load_host_private_key == NULL) {
75		r = SSH_ERR_INVALID_ARGUMENT;
76		goto out;
77	}
78	server_host_public = kex->load_host_public_key(kex->hostkey_type,
79	    kex->hostkey_nid, ssh);
80	server_host_private = kex->load_host_private_key(kex->hostkey_type,
81	    kex->hostkey_nid, ssh);
82	if (server_host_public == NULL) {
83		r = SSH_ERR_NO_HOSTKEY_LOADED;
84		goto out;
85	}
86
87	if ((r = sshpkt_get_string(ssh, &client_pubkey, &pklen)) != 0 ||
88	    (r = sshpkt_get_end(ssh)) != 0)
89		goto out;
90	if (pklen != CURVE25519_SIZE) {
91		r = SSH_ERR_SIGNATURE_INVALID;
92		goto out;
93	}
94#ifdef DEBUG_KEXECDH
95	dump_digest("client public key:", client_pubkey, CURVE25519_SIZE);
96#endif
97
98	if ((shared_secret = sshbuf_new()) == NULL) {
99		r = SSH_ERR_ALLOC_FAIL;
100		goto out;
101	}
102	if ((r = kexc25519_shared_key(server_key, client_pubkey,
103	    shared_secret)) < 0)
104		goto out;
105
106	/* calc H */
107	if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
108	    &sbloblen)) != 0)
109		goto out;
110	hashlen = sizeof(hash);
111	if ((r = kex_c25519_hash(
112	    kex->hash_alg,
113	    kex->client_version_string,
114	    kex->server_version_string,
115	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
116	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
117	    server_host_key_blob, sbloblen,
118	    client_pubkey,
119	    server_pubkey,
120	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
121	    hash, &hashlen)) < 0)
122		goto out;
123
124	/* save session id := H */
125	if (kex->session_id == NULL) {
126		kex->session_id_len = hashlen;
127		kex->session_id = malloc(kex->session_id_len);
128		if (kex->session_id == NULL) {
129			r = SSH_ERR_ALLOC_FAIL;
130			goto out;
131		}
132		memcpy(kex->session_id, hash, kex->session_id_len);
133	}
134
135	/* sign H */
136	if ((r = kex->sign(server_host_private, server_host_public, &signature,
137	     &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0)
138		goto out;
139
140	/* send server hostkey, ECDH pubkey 'Q_S' and signed H */
141	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
142	    (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
143	    (r = sshpkt_put_string(ssh, server_pubkey, sizeof(server_pubkey))) != 0 ||
144	    (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
145	    (r = sshpkt_send(ssh)) != 0)
146		goto out;
147
148	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
149		r = kex_send_newkeys(ssh);
150out:
151	explicit_bzero(hash, sizeof(hash));
152	explicit_bzero(server_key, sizeof(server_key));
153	free(server_host_key_blob);
154	free(signature);
155	free(client_pubkey);
156	sshbuf_free(shared_secret);
157	return r;
158}
159