1 /* $OpenBSD: kexecdhs.c,v 1.2 2010/09/22 05:01:29 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 "dh.h" 41 #include "ssh2.h" 42 #ifdef GSSAPI 43 #include "ssh-gss.h" 44 #endif 45 #include "monitor_wrap.h" 46 47 #ifdef OPENSSL_HAS_ECC 48 49 #include <openssl/ecdh.h> 50 51 void 52 kexecdh_server(Kex *kex) 53 { 54 EC_POINT *client_public; 55 EC_KEY *server_key; 56 const EC_GROUP *group; 57 BIGNUM *shared_secret; 58 Key *server_host_private, *server_host_public; 59 u_char *server_host_key_blob = NULL, *signature = NULL; 60 u_char *kbuf, *hash; 61 u_int klen, slen, sbloblen, hashlen; 62 int curve_nid; 63 64 if ((curve_nid = kex_ecdh_name_to_nid(kex->name)) == -1) 65 fatal("%s: unsupported ECDH curve \"%s\"", __func__, kex->name); 66 if ((server_key = EC_KEY_new_by_curve_name(curve_nid)) == NULL) 67 fatal("%s: EC_KEY_new_by_curve_name failed", __func__); 68 if (EC_KEY_generate_key(server_key) != 1) 69 fatal("%s: EC_KEY_generate_key failed", __func__); 70 group = EC_KEY_get0_group(server_key); 71 72 #ifdef DEBUG_KEXECDH 73 fputs("server private key:\n", stderr); 74 key_dump_ec_key(server_key); 75 #endif 76 77 if (kex->load_host_public_key == NULL || 78 kex->load_host_private_key == NULL) 79 fatal("Cannot load hostkey"); 80 server_host_public = kex->load_host_public_key(kex->hostkey_type); 81 if (server_host_public == NULL) 82 fatal("Unsupported hostkey type %d", kex->hostkey_type); 83 server_host_private = kex->load_host_private_key(kex->hostkey_type); 84 if (server_host_private == NULL) 85 fatal("Missing private key for hostkey type %d", 86 kex->hostkey_type); 87 88 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 89 packet_read_expect(SSH2_MSG_KEX_ECDH_INIT); 90 if ((client_public = EC_POINT_new(group)) == NULL) 91 fatal("%s: EC_POINT_new failed", __func__); 92 packet_get_ecpoint(group, client_public); 93 packet_check_eom(); 94 95 if (key_ec_validate_public(group, client_public) != 0) 96 fatal("%s: invalid client public key", __func__); 97 98 #ifdef DEBUG_KEXECDH 99 fputs("client public key:\n", stderr); 100 key_dump_ec_point(group, client_public); 101 #endif 102 103 /* Calculate shared_secret */ 104 klen = (EC_GROUP_get_degree(group) + 7) / 8; 105 kbuf = xmalloc(klen); 106 if (ECDH_compute_key(kbuf, klen, client_public, 107 server_key, NULL) != (int)klen) 108 fatal("%s: ECDH_compute_key failed", __func__); 109 110 #ifdef DEBUG_KEXDH 111 dump_digest("shared secret", kbuf, klen); 112 #endif 113 if ((shared_secret = BN_new()) == NULL) 114 fatal("%s: BN_new failed", __func__); 115 if (BN_bin2bn(kbuf, klen, shared_secret) == NULL) 116 fatal("%s: BN_bin2bn failed", __func__); 117 memset(kbuf, 0, klen); 118 xfree(kbuf); 119 120 /* calc H */ 121 key_to_blob(server_host_public, &server_host_key_blob, &sbloblen); 122 kex_ecdh_hash( 123 kex->evp_md, 124 group, 125 kex->client_version_string, 126 kex->server_version_string, 127 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 128 buffer_ptr(&kex->my), buffer_len(&kex->my), 129 server_host_key_blob, sbloblen, 130 client_public, 131 EC_KEY_get0_public_key(server_key), 132 shared_secret, 133 &hash, &hashlen 134 ); 135 EC_POINT_clear_free(client_public); 136 137 /* save session id := H */ 138 if (kex->session_id == NULL) { 139 kex->session_id_len = hashlen; 140 kex->session_id = xmalloc(kex->session_id_len); 141 memcpy(kex->session_id, hash, kex->session_id_len); 142 } 143 144 /* sign H */ 145 if (PRIVSEP(key_sign(server_host_private, &signature, &slen, 146 hash, hashlen)) < 0) 147 fatal("kexdh_server: key_sign failed"); 148 149 /* destroy_sensitive_data(); */ 150 151 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 152 packet_start(SSH2_MSG_KEX_ECDH_REPLY); 153 packet_put_string(server_host_key_blob, sbloblen); 154 packet_put_ecpoint(group, EC_KEY_get0_public_key(server_key)); 155 packet_put_string(signature, slen); 156 packet_send(); 157 158 xfree(signature); 159 xfree(server_host_key_blob); 160 /* have keys, free server key */ 161 EC_KEY_free(server_key); 162 163 kex_derive_keys(kex, hash, hashlen, shared_secret); 164 BN_clear_free(shared_secret); 165 kex_finish(kex); 166 } 167 #else /* OPENSSL_HAS_ECC */ 168 void 169 kexecdh_server(Kex *kex) 170 { 171 fatal("ECC support is not enabled"); 172 } 173 #endif /* OPENSSL_HAS_ECC */ 174
