kexecdhs.c revision 262566
1/* $OpenBSD: kexecdhs.c,v 1.9 2014/01/12 08:13:13 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#include <sys/types.h> 30#include <string.h> 31#include <signal.h> 32 33#include "xmalloc.h" 34#include "buffer.h" 35#include "key.h" 36#include "cipher.h" 37#include "kex.h" 38#include "log.h" 39#include "packet.h" 40#include "ssh2.h" 41 42#ifdef OPENSSL_HAS_ECC 43 44#include <openssl/ecdh.h> 45 46void 47kexecdh_server(Kex *kex) 48{ 49 EC_POINT *client_public; 50 EC_KEY *server_key; 51 const EC_GROUP *group; 52 BIGNUM *shared_secret; 53 Key *server_host_private, *server_host_public; 54 u_char *server_host_key_blob = NULL, *signature = NULL; 55 u_char *kbuf, *hash; 56 u_int klen, slen, sbloblen, hashlen; 57 58 if ((server_key = EC_KEY_new_by_curve_name(kex->ec_nid)) == NULL) 59 fatal("%s: EC_KEY_new_by_curve_name failed", __func__); 60 if (EC_KEY_generate_key(server_key) != 1) 61 fatal("%s: EC_KEY_generate_key failed", __func__); 62 group = EC_KEY_get0_group(server_key); 63 64#ifdef DEBUG_KEXECDH 65 fputs("server private key:\n", stderr); 66 key_dump_ec_key(server_key); 67#endif 68 69 if (kex->load_host_public_key == NULL || 70 kex->load_host_private_key == NULL) 71 fatal("Cannot load hostkey"); 72 server_host_public = kex->load_host_public_key(kex->hostkey_type); 73 if (server_host_public == NULL) 74 fatal("Unsupported hostkey type %d", kex->hostkey_type); 75 server_host_private = kex->load_host_private_key(kex->hostkey_type); 76 77 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 78 packet_read_expect(SSH2_MSG_KEX_ECDH_INIT); 79 if ((client_public = EC_POINT_new(group)) == NULL) 80 fatal("%s: EC_POINT_new failed", __func__); 81 packet_get_ecpoint(group, client_public); 82 packet_check_eom(); 83 84 if (key_ec_validate_public(group, client_public) != 0) 85 fatal("%s: invalid client public key", __func__); 86 87#ifdef DEBUG_KEXECDH 88 fputs("client public key:\n", stderr); 89 key_dump_ec_point(group, client_public); 90#endif 91 92 /* Calculate shared_secret */ 93 klen = (EC_GROUP_get_degree(group) + 7) / 8; 94 kbuf = xmalloc(klen); 95 if (ECDH_compute_key(kbuf, klen, client_public, 96 server_key, NULL) != (int)klen) 97 fatal("%s: ECDH_compute_key failed", __func__); 98 99#ifdef DEBUG_KEXDH 100 dump_digest("shared secret", kbuf, klen); 101#endif 102 if ((shared_secret = BN_new()) == NULL) 103 fatal("%s: BN_new failed", __func__); 104 if (BN_bin2bn(kbuf, klen, shared_secret) == NULL) 105 fatal("%s: BN_bin2bn failed", __func__); 106 memset(kbuf, 0, klen); 107 free(kbuf); 108 109 /* calc H */ 110 key_to_blob(server_host_public, &server_host_key_blob, &sbloblen); 111 kex_ecdh_hash( 112 kex->hash_alg, 113 group, 114 kex->client_version_string, 115 kex->server_version_string, 116 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 117 buffer_ptr(&kex->my), buffer_len(&kex->my), 118 server_host_key_blob, sbloblen, 119 client_public, 120 EC_KEY_get0_public_key(server_key), 121 shared_secret, 122 &hash, &hashlen 123 ); 124 EC_POINT_clear_free(client_public); 125 126 /* save session id := H */ 127 if (kex->session_id == NULL) { 128 kex->session_id_len = hashlen; 129 kex->session_id = xmalloc(kex->session_id_len); 130 memcpy(kex->session_id, hash, kex->session_id_len); 131 } 132 133 /* sign H */ 134 kex->sign(server_host_private, server_host_public, &signature, &slen, 135 hash, hashlen); 136 137 /* destroy_sensitive_data(); */ 138 139 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 140 packet_start(SSH2_MSG_KEX_ECDH_REPLY); 141 packet_put_string(server_host_key_blob, sbloblen); 142 packet_put_ecpoint(group, EC_KEY_get0_public_key(server_key)); 143 packet_put_string(signature, slen); 144 packet_send(); 145 146 free(signature); 147 free(server_host_key_blob); 148 /* have keys, free server key */ 149 EC_KEY_free(server_key); 150 151 kex_derive_keys_bn(kex, hash, hashlen, shared_secret); 152 BN_clear_free(shared_secret); 153 kex_finish(kex); 154} 155#else /* OPENSSL_HAS_ECC */ 156void 157kexecdh_server(Kex *kex) 158{ 159 fatal("ECC support is not enabled"); 160} 161#endif /* OPENSSL_HAS_ECC */ 162