1/* $OpenBSD: kexc25519c.c,v 1.9 2017/12/18 02:25:15 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, struct ssh *ssh);
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, struct ssh *ssh)
73{
74	struct kex *kex = ssh->kex;
75	struct sshkey *server_host_key = NULL;
76	struct sshbuf *shared_secret = NULL;
77	u_char *server_pubkey = NULL;
78	u_char *server_host_key_blob = NULL, *signature = NULL;
79	u_char hash[SSH_DIGEST_MAX_LENGTH];
80	size_t slen, pklen, sbloblen, hashlen;
81	int r;
82
83	if (kex->verify_host_key == NULL) {
84		r = SSH_ERR_INVALID_ARGUMENT;
85		goto out;
86	}
87
88	/* hostkey */
89	if ((r = sshpkt_get_string(ssh, &server_host_key_blob,
90	    &sbloblen)) != 0 ||
91	    (r = sshkey_from_blob(server_host_key_blob, sbloblen,
92	    &server_host_key)) != 0)
93		goto out;
94	if (server_host_key->type != kex->hostkey_type ||
95	    (kex->hostkey_type == KEY_ECDSA &&
96	    server_host_key->ecdsa_nid != kex->hostkey_nid)) {
97		r = SSH_ERR_KEY_TYPE_MISMATCH;
98		goto out;
99	}
100	if (kex->verify_host_key(server_host_key, ssh) == -1) {
101		r = SSH_ERR_SIGNATURE_INVALID;
102		goto out;
103	}
104
105	/* Q_S, server public key */
106	/* signed H */
107	if ((r = sshpkt_get_string(ssh, &server_pubkey, &pklen)) != 0 ||
108	    (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
109	    (r = sshpkt_get_end(ssh)) != 0)
110		goto out;
111	if (pklen != CURVE25519_SIZE) {
112		r = SSH_ERR_SIGNATURE_INVALID;
113		goto out;
114	}
115
116#ifdef DEBUG_KEXECDH
117	dump_digest("server public key:", server_pubkey, CURVE25519_SIZE);
118#endif
119
120	if ((shared_secret = sshbuf_new()) == NULL) {
121		r = SSH_ERR_ALLOC_FAIL;
122		goto out;
123	}
124	if ((r = kexc25519_shared_key(kex->c25519_client_key, server_pubkey,
125	    shared_secret)) < 0)
126		goto out;
127
128	/* calc and verify H */
129	hashlen = sizeof(hash);
130	if ((r = kex_c25519_hash(
131	    kex->hash_alg,
132	    kex->client_version_string,
133	    kex->server_version_string,
134	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
135	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
136	    server_host_key_blob, sbloblen,
137	    kex->c25519_client_pubkey,
138	    server_pubkey,
139	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
140	    hash, &hashlen)) < 0)
141		goto out;
142
143	if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen,
144	    kex->hostkey_alg, ssh->compat)) != 0)
145		goto out;
146
147	/* save session id */
148	if (kex->session_id == NULL) {
149		kex->session_id_len = hashlen;
150		kex->session_id = malloc(kex->session_id_len);
151		if (kex->session_id == NULL) {
152			r = SSH_ERR_ALLOC_FAIL;
153			goto out;
154		}
155		memcpy(kex->session_id, hash, kex->session_id_len);
156	}
157
158	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
159		r = kex_send_newkeys(ssh);
160out:
161	explicit_bzero(hash, sizeof(hash));
162	explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key));
163	free(server_host_key_blob);
164	free(server_pubkey);
165	free(signature);
166	sshkey_free(server_host_key);
167	sshbuf_free(shared_secret);
168	return r;
169}
170