1/* $OpenBSD: kexecdhs.c,v 1.17 2018/02/07 02:06:51 jsing 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 50static int input_kex_ecdh_init(int, u_int32_t, struct ssh *); 51 52int 53kexecdh_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 60static int 61input_kex_ecdh_init(int type, u_int32_t seq, struct ssh *ssh) 62{ 63 struct kex *kex = ssh->kex; 64 EC_POINT *client_public; 65 EC_KEY *server_key = NULL; 66 const EC_GROUP *group; 67 const EC_POINT *public_key; 68 BIGNUM *shared_secret = NULL; 69 struct sshkey *server_host_private, *server_host_public; 70 u_char *server_host_key_blob = NULL, *signature = NULL; 71 u_char *kbuf = NULL; 72 u_char hash[SSH_DIGEST_MAX_LENGTH]; 73 size_t slen, sbloblen; 74 size_t klen = 0, hashlen; 75 int r; 76 77 if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) { 78 r = SSH_ERR_ALLOC_FAIL; 79 goto out; 80 } 81 if (EC_KEY_generate_key(server_key) != 1) { 82 r = SSH_ERR_LIBCRYPTO_ERROR; 83 goto out; 84 } 85 group = EC_KEY_get0_group(server_key); 86 87#ifdef DEBUG_KEXECDH 88 fputs("server private key:\n", stderr); 89 sshkey_dump_ec_key(server_key); 90#endif 91 92 if (kex->load_host_public_key == NULL || 93 kex->load_host_private_key == NULL) { 94 r = SSH_ERR_INVALID_ARGUMENT; 95 goto out; 96 } 97 server_host_public = kex->load_host_public_key(kex->hostkey_type, 98 kex->hostkey_nid, ssh); 99 server_host_private = kex->load_host_private_key(kex->hostkey_type, 100 kex->hostkey_nid, ssh); 101 if (server_host_public == NULL) { 102 r = SSH_ERR_NO_HOSTKEY_LOADED; 103 goto out; 104 } 105 if ((client_public = EC_POINT_new(group)) == NULL) { 106 r = SSH_ERR_ALLOC_FAIL; 107 goto out; 108 } 109 if ((r = sshpkt_get_ec(ssh, client_public, group)) != 0 || 110 (r = sshpkt_get_end(ssh)) != 0) 111 goto out; 112 113#ifdef DEBUG_KEXECDH 114 fputs("client public key:\n", stderr); 115 sshkey_dump_ec_point(group, client_public); 116#endif 117 if (sshkey_ec_validate_public(group, client_public) != 0) { 118 sshpkt_disconnect(ssh, "invalid client public key"); 119 r = SSH_ERR_MESSAGE_INCOMPLETE; 120 goto out; 121 } 122 123 /* Calculate shared_secret */ 124 klen = (EC_GROUP_get_degree(group) + 7) / 8; 125 if ((kbuf = malloc(klen)) == NULL || 126 (shared_secret = BN_new()) == NULL) { 127 r = SSH_ERR_ALLOC_FAIL; 128 goto out; 129 } 130 if (ECDH_compute_key(kbuf, klen, client_public, 131 server_key, NULL) != (int)klen || 132 BN_bin2bn(kbuf, klen, shared_secret) == NULL) { 133 r = SSH_ERR_LIBCRYPTO_ERROR; 134 goto out; 135 } 136 137#ifdef DEBUG_KEXECDH 138 dump_digest("shared secret", kbuf, klen); 139#endif 140 /* calc H */ 141 if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob, 142 &sbloblen)) != 0) 143 goto out; 144 hashlen = sizeof(hash); 145 if ((r = kex_ecdh_hash( 146 kex->hash_alg, 147 group, 148 kex->client_version_string, 149 kex->server_version_string, 150 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer), 151 sshbuf_ptr(kex->my), sshbuf_len(kex->my), 152 server_host_key_blob, sbloblen, 153 client_public, 154 EC_KEY_get0_public_key(server_key), 155 shared_secret, 156 hash, &hashlen)) != 0) 157 goto out; 158 159 /* save session id := H */ 160 if (kex->session_id == NULL) { 161 kex->session_id_len = hashlen; 162 kex->session_id = malloc(kex->session_id_len); 163 if (kex->session_id == NULL) { 164 r = SSH_ERR_ALLOC_FAIL; 165 goto out; 166 } 167 memcpy(kex->session_id, hash, kex->session_id_len); 168 } 169 170 /* sign H */ 171 if ((r = kex->sign(server_host_private, server_host_public, &signature, 172 &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0) 173 goto out; 174 175 /* destroy_sensitive_data(); */ 176 177 public_key = EC_KEY_get0_public_key(server_key); 178 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 179 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 180 (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 || 181 (r = sshpkt_put_ec(ssh, public_key, group)) != 0 || 182 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 183 (r = sshpkt_send(ssh)) != 0) 184 goto out; 185 186 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0) 187 r = kex_send_newkeys(ssh); 188 out: 189 explicit_bzero(hash, sizeof(hash)); 190 EC_KEY_free(kex->ec_client_key); 191 kex->ec_client_key = NULL; 192 EC_KEY_free(server_key); 193 if (kbuf) { 194 explicit_bzero(kbuf, klen); 195 free(kbuf); 196 } 197 BN_clear_free(shared_secret); 198 free(server_host_key_blob); 199 free(signature); 200 return r; 201} 202#endif /* defined(WITH_OPENSSL) && defined(OPENSSL_HAS_ECC) */ 203 204