1/* $OpenBSD: kexc25519c.c,v 1.7 2015/01/26 06:10:03 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 * 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 <stdio.h>
33#include <string.h>
34#include <signal.h>
35
36#include "sshkey.h"
37#include "cipher.h"
38#include "kex.h"
39#include "log.h"
40#include "packet.h"
41#include "ssh2.h"
42#include "sshbuf.h"
43#include "digest.h"
44#include "ssherr.h"
45
46static int
47input_kex_c25519_reply(int type, u_int32_t seq, void *ctxt);
48
49int
50kexc25519_client(struct ssh *ssh)
51{
52	struct kex *kex = ssh->kex;
53	int r;
54
55	kexc25519_keygen(kex->c25519_client_key, kex->c25519_client_pubkey);
56#ifdef DEBUG_KEXECDH
57	dump_digest("client private key:", kex->c25519_client_key,
58	    sizeof(kex->c25519_client_key));
59#endif
60	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 ||
61	    (r = sshpkt_put_string(ssh, kex->c25519_client_pubkey,
62	    sizeof(kex->c25519_client_pubkey))) != 0 ||
63	    (r = sshpkt_send(ssh)) != 0)
64		return r;
65
66	debug("expecting SSH2_MSG_KEX_ECDH_REPLY");
67	ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_c25519_reply);
68	return 0;
69}
70
71static int
72input_kex_c25519_reply(int type, u_int32_t seq, void *ctxt)
73{
74	struct ssh *ssh = ctxt;
75	struct kex *kex = ssh->kex;
76	struct sshkey *server_host_key = NULL;
77	struct sshbuf *shared_secret = NULL;
78	u_char *server_pubkey = NULL;
79	u_char *server_host_key_blob = NULL, *signature = NULL;
80	u_char hash[SSH_DIGEST_MAX_LENGTH];
81	size_t slen, pklen, sbloblen, hashlen;
82	int r;
83
84	if (kex->verify_host_key == NULL) {
85		r = SSH_ERR_INVALID_ARGUMENT;
86		goto out;
87	}
88
89	/* hostkey */
90	if ((r = sshpkt_get_string(ssh, &server_host_key_blob,
91	    &sbloblen)) != 0 ||
92	    (r = sshkey_from_blob(server_host_key_blob, sbloblen,
93	    &server_host_key)) != 0)
94		goto out;
95	if (server_host_key->type != kex->hostkey_type ||
96	    (kex->hostkey_type == KEY_ECDSA &&
97	    server_host_key->ecdsa_nid != kex->hostkey_nid)) {
98		r = SSH_ERR_KEY_TYPE_MISMATCH;
99		goto out;
100	}
101	if (kex->verify_host_key(server_host_key, ssh) == -1) {
102		r = SSH_ERR_SIGNATURE_INVALID;
103		goto out;
104	}
105
106	/* Q_S, server public key */
107	/* signed H */
108	if ((r = sshpkt_get_string(ssh, &server_pubkey, &pklen)) != 0 ||
109	    (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
110	    (r = sshpkt_get_end(ssh)) != 0)
111		goto out;
112	if (pklen != CURVE25519_SIZE) {
113		r = SSH_ERR_SIGNATURE_INVALID;
114		goto out;
115	}
116
117#ifdef DEBUG_KEXECDH
118	dump_digest("server public key:", server_pubkey, CURVE25519_SIZE);
119#endif
120
121	if ((shared_secret = sshbuf_new()) == NULL) {
122		r = SSH_ERR_ALLOC_FAIL;
123		goto out;
124	}
125	if ((r = kexc25519_shared_key(kex->c25519_client_key, server_pubkey,
126	    shared_secret)) < 0)
127		goto out;
128
129	/* calc and verify H */
130	hashlen = sizeof(hash);
131	if ((r = kex_c25519_hash(
132	    kex->hash_alg,
133	    kex->client_version_string,
134	    kex->server_version_string,
135	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
136	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
137	    server_host_key_blob, sbloblen,
138	    kex->c25519_client_pubkey,
139	    server_pubkey,
140	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
141	    hash, &hashlen)) < 0)
142		goto out;
143
144	if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen,
145	    ssh->compat)) != 0)
146		goto out;
147
148	/* save session id */
149	if (kex->session_id == NULL) {
150		kex->session_id_len = hashlen;
151		kex->session_id = malloc(kex->session_id_len);
152		if (kex->session_id == NULL) {
153			r = SSH_ERR_ALLOC_FAIL;
154			goto out;
155		}
156		memcpy(kex->session_id, hash, kex->session_id_len);
157	}
158
159	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
160		r = kex_send_newkeys(ssh);
161out:
162	explicit_bzero(hash, sizeof(hash));
163	explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key));
164	free(server_host_key_blob);
165	free(server_pubkey);
166	free(signature);
167	sshkey_free(server_host_key);
168	sshbuf_free(shared_secret);
169	return r;
170}
171