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
44static int input_kex_c25519_init(int, u_int32_t, void *);
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, 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);
151out:
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