1 /* 2 * Copyright (c) 2001 Markus Friedl. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 23 */ 24 25 #include "includes.h" 26 RCSID("$OpenBSD: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $"); 27 28 #pragma ident "%Z%%M% %I% %E% SMI" 29 30 #include <openssl/crypto.h> 31 #include <openssl/bn.h> 32 33 #include "xmalloc.h" 34 #include "buffer.h" 35 #include "bufaux.h" 36 #include "key.h" 37 #include "kex.h" 38 #include "log.h" 39 #include "packet.h" 40 #include "dh.h" 41 #include "ssh2.h" 42 43 void 44 kexdh_server(Kex *kex) 45 { 46 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 47 DH *dh; 48 Key *server_host_key; 49 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; 50 u_int sbloblen, klen, kout; 51 u_int slen; 52 53 /* generate server DH public key */ 54 dh = dh_new_group1(); 55 dh_gen_key(dh, kex->we_need * 8); 56 57 debug("expecting SSH2_MSG_KEXDH_INIT"); 58 packet_read_expect(SSH2_MSG_KEXDH_INIT); 59 60 if (kex->load_host_key == NULL) 61 fatal("Cannot load hostkey"); 62 server_host_key = kex->load_host_key(kex->hostkey_type); 63 if (server_host_key == NULL) 64 fatal("Unsupported hostkey type %d", kex->hostkey_type); 65 66 /* key, cert */ 67 if ((dh_client_pub = BN_new()) == NULL) 68 fatal("dh_client_pub == NULL"); 69 packet_get_bignum2(dh_client_pub); 70 packet_check_eom(); 71 72 #ifdef DEBUG_KEXDH 73 fprintf(stderr, "dh_client_pub= "); 74 BN_print_fp(stderr, dh_client_pub); 75 fprintf(stderr, "\n"); 76 debug("bits %d", BN_num_bits(dh_client_pub)); 77 #endif 78 79 #ifdef DEBUG_KEXDH 80 DHparams_print_fp(stderr, dh); 81 fprintf(stderr, "pub= "); 82 BN_print_fp(stderr, dh->pub_key); 83 fprintf(stderr, "\n"); 84 #endif 85 if (!dh_pub_is_valid(dh, dh_client_pub)) 86 packet_disconnect("bad client public DH value"); 87 88 klen = DH_size(dh); 89 kbuf = xmalloc(klen); 90 kout = DH_compute_key(kbuf, dh_client_pub, dh); 91 #ifdef DEBUG_KEXDH 92 dump_digest("shared secret", kbuf, kout); 93 #endif 94 if ((shared_secret = BN_new()) == NULL) 95 fatal("kexdh_server: BN_new failed"); 96 BN_bin2bn(kbuf, kout, shared_secret); 97 memset(kbuf, 0, klen); 98 xfree(kbuf); 99 100 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); 101 102 /* calc H */ 103 hash = kex_dh_hash( 104 kex->client_version_string, 105 kex->server_version_string, 106 buffer_ptr(&kex->peer), buffer_len(&kex->peer), 107 buffer_ptr(&kex->my), buffer_len(&kex->my), 108 server_host_key_blob, sbloblen, 109 dh_client_pub, 110 dh->pub_key, 111 shared_secret 112 ); 113 BN_clear_free(dh_client_pub); 114 115 /* save session id := H */ 116 /* XXX hashlen depends on KEX */ 117 if (kex->session_id == NULL) { 118 kex->session_id_len = 20; 119 kex->session_id = xmalloc(kex->session_id_len); 120 memcpy(kex->session_id, hash, kex->session_id_len); 121 } 122 123 /* sign H */ 124 /* XXX hashlen depends on KEX */ 125 key_sign(server_host_key, &signature, &slen, hash, 20); 126 127 /* destroy_sensitive_data(); */ 128 129 /* send server hostkey, DH pubkey 'f' and singed H */ 130 packet_start(SSH2_MSG_KEXDH_REPLY); 131 packet_put_string(server_host_key_blob, sbloblen); 132 packet_put_bignum2(dh->pub_key); /* f */ 133 packet_put_string(signature, slen); 134 packet_send(); 135 136 xfree(signature); 137 xfree(server_host_key_blob); 138 /* have keys, free DH */ 139 DH_free(dh); 140 141 kex_derive_keys(kex, hash, shared_secret); 142 BN_clear_free(shared_secret); 143 kex_finish(kex); 144 } 145