Home | History | Annotate | Download | only in openssh
      1 /* $OpenBSD: kexecdhs.c,v 1.14 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  *
      6  * Redistribution and use in source and binary forms, with or without
      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 #if defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC)
     30 
     31 #include <sys/types.h>
     32 #include <string.h>
     33 #include <signal.h>
     34 
     35 #include <openssl/ecdh.h>
     36 
     37 #include "sshkey.h"
     38 #include "cipher.h"
     39 #include "digest.h"
     40 #include "kex.h"
     41 #include "log.h"
     42 #include "packet.h"
     43 #include "ssh2.h"
     44 
     45 #include "dispatch.h"
     46 #include "compat.h"
     47 #include "ssherr.h"
     48 #include "sshbuf.h"
     49 
     50 static int input_kex_ecdh_init(int, u_int32_t, void *);
     51 
     52 int
     53 kexecdh_server(struct ssh *ssh)
     54 {
     55 	debug("expecting SSH2_MSG_KEX_ECDH_INIT");
     56 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_ecdh_init);
     57 	return 0;
     58 }
     59 
     60 static int
     61 input_kex_ecdh_init(int type, u_int32_t seq, void *ctxt)
     62 {
     63 	struct ssh *ssh = ctxt;
     64 	struct kex *kex = ssh->kex;
     65 	EC_POINT *client_public;
     66 	EC_KEY *server_key = NULL;
     67 	const EC_GROUP *group;
     68 	const EC_POINT *public_key;
     69 	BIGNUM *shared_secret = NULL;
     70 	struct sshkey *server_host_private, *server_host_public;
     71 	u_char *server_host_key_blob = NULL, *signature = NULL;
     72 	u_char *kbuf = NULL;
     73 	u_char hash[SSH_DIGEST_MAX_LENGTH];
     74 	size_t slen, sbloblen;
     75 	size_t klen = 0, hashlen;
     76 	int r;
     77 
     78 	if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) {
     79 		r = SSH_ERR_ALLOC_FAIL;
     80 		goto out;
     81 	}
     82 	if (EC_KEY_generate_key(server_key) != 1) {
     83 		r = SSH_ERR_LIBCRYPTO_ERROR;
     84 		goto out;
     85 	}
     86 	group = EC_KEY_get0_group(server_key);
     87 
     88 #ifdef DEBUG_KEXECDH
     89 	fputs("server private key:\n", stderr);
     90 	sshkey_dump_ec_key(server_key);
     91 #endif
     92 
     93 	if (kex->load_host_public_key == NULL ||
     94 	    kex->load_host_private_key == NULL) {
     95 		r = SSH_ERR_INVALID_ARGUMENT;
     96 		goto out;
     97 	}
     98 	server_host_public = kex->load_host_public_key(kex->hostkey_type,
     99 	    kex->hostkey_nid, ssh);
    100 	server_host_private = kex->load_host_private_key(kex->hostkey_type,
    101 	    kex->hostkey_nid, ssh);
    102 	if (server_host_public == NULL) {
    103 		r = SSH_ERR_NO_HOSTKEY_LOADED;
    104 		goto out;
    105 	}
    106 	if ((client_public = EC_POINT_new(group)) == NULL) {
    107 		r = SSH_ERR_ALLOC_FAIL;
    108 		goto out;
    109 	}
    110 	if ((r = sshpkt_get_ec(ssh, client_public, group)) != 0 ||
    111 	    (r = sshpkt_get_end(ssh)) != 0)
    112 		goto out;
    113 
    114 #ifdef DEBUG_KEXECDH
    115 	fputs("client public key:\n", stderr);
    116 	sshkey_dump_ec_point(group, client_public);
    117 #endif
    118 	if (sshkey_ec_validate_public(group, client_public) != 0) {
    119 		sshpkt_disconnect(ssh, "invalid client public key");
    120 		r = SSH_ERR_MESSAGE_INCOMPLETE;
    121 		goto out;
    122 	}
    123 
    124 	/* Calculate shared_secret */
    125 	klen = (EC_GROUP_get_degree(group) + 7) / 8;
    126 	if ((kbuf = malloc(klen)) == NULL ||
    127 	    (shared_secret = BN_new()) == NULL) {
    128 		r = SSH_ERR_ALLOC_FAIL;
    129 		goto out;
    130 	}
    131 	if (ECDH_compute_key(kbuf, klen, client_public,
    132 	    server_key, NULL) != (int)klen ||
    133 	    BN_bin2bn(kbuf, klen, shared_secret) == NULL) {
    134 		r = SSH_ERR_LIBCRYPTO_ERROR;
    135 		goto out;
    136 	}
    137 
    138 #ifdef DEBUG_KEXECDH
    139 	dump_digest("shared secret", kbuf, klen);
    140 #endif
    141 	/* calc H */
    142 	if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob,
    143 	    &sbloblen)) != 0)
    144 		goto out;
    145 	hashlen = sizeof(hash);
    146 	if ((r = kex_ecdh_hash(
    147 	    kex->hash_alg,
    148 	    group,
    149 	    kex->client_version_string,
    150 	    kex->server_version_string,
    151 	    sshbuf_ptr(kex->peer), sshbuf_len(kex->peer),
    152 	    sshbuf_ptr(kex->my), sshbuf_len(kex->my),
    153 	    server_host_key_blob, sbloblen,
    154 	    client_public,
    155 	    EC_KEY_get0_public_key(server_key),
    156 	    shared_secret,
    157 	    hash, &hashlen)) != 0)
    158 		goto out;
    159 
    160 	/* save session id := H */
    161 	if (kex->session_id == NULL) {
    162 		kex->session_id_len = hashlen;
    163 		kex->session_id = malloc(kex->session_id_len);
    164 		if (kex->session_id == NULL) {
    165 			r = SSH_ERR_ALLOC_FAIL;
    166 			goto out;
    167 		}
    168 		memcpy(kex->session_id, hash, kex->session_id_len);
    169 	}
    170 
    171 	/* sign H */
    172 	if ((r = kex->sign(server_host_private, server_host_public,
    173 	    &signature, &slen, hash, hashlen, ssh->compat)) < 0)
    174 		goto out;
    175 
    176 	/* destroy_sensitive_data(); */
    177 
    178 	public_key = EC_KEY_get0_public_key(server_key);
    179 	/* send server hostkey, ECDH pubkey 'Q_S' and signed H */
    180 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
    181 	    (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 ||
    182 	    (r = sshpkt_put_ec(ssh, public_key, group)) != 0 ||
    183 	    (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
    184 	    (r = sshpkt_send(ssh)) != 0)
    185 		goto out;
    186 
    187 	if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0)
    188 		r = kex_send_newkeys(ssh);
    189  out:
    190 	explicit_bzero(hash, sizeof(hash));
    191 	if (kex->ec_client_key) {
    192 		EC_KEY_free(kex->ec_client_key);
    193 		kex->ec_client_key = NULL;
    194 	}
    195 	if (server_key)
    196 		EC_KEY_free(server_key);
    197 	if (kbuf) {
    198 		explicit_bzero(kbuf, klen);
    199 		free(kbuf);
    200 	}
    201 	if (shared_secret)
    202 		BN_clear_free(shared_secret);
    203 	free(server_host_key_blob);
    204 	free(signature);
    205 	return r;
    206 }
    207 #endif /* defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC) */
    208 
    209