1 /* $OpenBSD: kexecdhc.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 31 #include <stdio.h> 32 #include <string.h> 33 #include <signal.h> 34 35 #include "xmalloc.h" 36 #include "buffer.h" 37 #include "key.h" 38 #include "cipher.h" 39 #include "kex.h" 40 #include "log.h" 41 #include "packet.h" 42 #include "dh.h" 43 #include "ssh2.h" 44 45 #ifdef OPENSSL_HAS_ECC 46 47 #include <openssl/ecdh.h> 48 49 void 50 kexecdh_client(Kex *kex) 51 { 52 EC_KEY *client_key; 53 EC_POINT *server_public; 54 const EC_GROUP *group; 55 BIGNUM *shared_secret; 56 Key *server_host_key; 57 u_char *server_host_key_blob = NULL, *signature = NULL; 58 u_char *kbuf, *hash; 59 u_int klen, slen, sbloblen, hashlen; 60 int curve_nid; 61 62 if ((curve_nid = kex_ecdh_name_to_nid(kex->name)) == -1) 63 fatal("%s: unsupported ECDH curve \"%s\"", __func__, kex->name); 64 if ((client_key = EC_KEY_new_by_curve_name(curve_nid)) == NULL) 65 fatal("%s: EC_KEY_new_by_curve_name failed", __func__); 66 if (EC_KEY_generate_key(client_key) != 1) 67 fatal("%s: EC_KEY_generate_key failed", __func__); 68 group = EC_KEY_get0_group(client_key); 69 70 packet_start(SSH2_MSG_KEX_ECDH_INIT); 71 packet_put_ecpoint(group, EC_KEY_get0_public_key(client_key)); 72 packet_send(); 73 debug("sending SSH2_MSG_KEX_ECDH_INIT"); 74 75 #ifdef DEBUG_KEXECDH 76 fputs("client private key:\n", stderr); 77 key_dump_ec_key(client_key); 78 #endif 79 80 debug("expecting SSH2_MSG_KEX_ECDH_REPLY"); 81 packet_read_expect(SSH2_MSG_KEX_ECDH_REPLY); 82 83 /* hostkey */ 84 server_host_key_blob = packet_get_string(&sbloblen); 85 server_host_key = key_from_blob(server_host_key_blob, sbloblen); 86 if (server_host_key == NULL) 87 fatal("cannot decode server_host_key_blob"); 88 if (server_host_key->type != kex->hostkey_type) 89 fatal("type mismatch for decoded server_host_key_blob"); 90 if (kex->verify_host_key == NULL) 91 fatal("cannot verify server_host_key"); 92 if (kex->verify_host_key(server_host_key) == -1) 93 fatal("server_host_key verification failed"); 94 95 /* Q_S, server public key */ 96 if ((server_public = EC_POINT_new(group)) == NULL) 97 fatal("%s: EC_POINT_new failed", __func__); 98 packet_get_ecpoint(group, server_public); 99 100 if (key_ec_validate_public(group, server_public) != 0) 101 fatal("%s: invalid server public key", __func__); 102 103 #ifdef DEBUG_KEXECDH 104 fputs("server public key:\n", stderr); 105 key_dump_ec_point(group, server_public); 106 #endif 107 108 /* signed H */ 109 signature = packet_get_string(&slen); 110 packet_check_eom(); 111 112 klen = (EC_GROUP_get_degree(group) + 7) / 8; 113 kbuf = xmalloc(klen); 114 if (ECDH_compute_key(kbuf, klen, server_public, 115 client_key, NULL) != (int)klen) 116 fatal("%s: ECDH_compute_key failed", __func__); 117 118 #ifdef DEBUG_KEXECDH 119 dump_digest("shared secret", kbuf, klen); 120 #endif 121 if ((shared_secret = BN_new()) == NULL) 122 fatal("%s: BN_new failed", __func__); 123 if (BN_bin2bn(kbuf, klen, shared_secret) == NULL) 124 fatal("%s: BN_bin2bn failed", __func__); 125 memset(kbuf, 0, klen); 126 xfree(kbuf); 127 128 /* calc and verify H */ 129 kex_ecdh_hash( 130 kex->evp_md, 131 group, 132 kex->client_version_string, 133 kex->server_version_string, 134 buffer_ptr(&kex->my), buffer_len(&kex->my), 135 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 136 server_host_key_blob, sbloblen, 137 EC_KEY_get0_public_key(client_key), 138 server_public, 139 shared_secret, 140 &hash, &hashlen 141 ); 142 xfree(server_host_key_blob); 143 EC_POINT_clear_free(server_public); 144 EC_KEY_free(client_key); 145 146 if (key_verify(server_host_key, signature, slen, hash, hashlen) != 1) 147 fatal("key_verify failed for server_host_key"); 148 key_free(server_host_key); 149 xfree(signature); 150 151 /* save session id */ 152 if (kex->session_id == NULL) { 153 kex->session_id_len = hashlen; 154 kex->session_id = xmalloc(kex->session_id_len); 155 memcpy(kex->session_id, hash, kex->session_id_len); 156 } 157 158 kex_derive_keys(kex, hash, hashlen, shared_secret); 159 BN_clear_free(shared_secret); 160 kex_finish(kex); 161 } 162 #else /* OPENSSL_HAS_ECC */ 163 void 164 kexecdh_client(Kex *kex) 165 { 166 fatal("ECC support is not enabled"); 167 } 168 #endif /* OPENSSL_HAS_ECC */ 169
