1 /* $OpenBSD: kexecdhs.c,v 1.15 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 * 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, &signature, 173 &slen, hash, hashlen, kex->hostkey_alg, 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
