1 /* $OpenBSD: kexgexs.c,v 1.29 2016/06/08 02:13:01 dtucker Exp $ */ 2 /* 3 * Copyright (c) 2000 Niels Provos. All rights reserved. 4 * Copyright (c) 2001 Markus Friedl. 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 <sys/param.h> /* MIN MAX */ 28 29 #include <stdio.h> 30 #include <string.h> 31 #include <signal.h> 32 33 #include <openssl/dh.h> 34 35 #include "sshkey.h" 36 #include "cipher.h" 37 #include "digest.h" 38 #include "kex.h" 39 #include "log.h" 40 #include "packet.h" 41 #include "dh.h" 42 #include "ssh2.h" 43 #include "compat.h" 44 #ifdef GSSAPI 45 #include "ssh-gss.h" 46 #endif 47 #include "monitor_wrap.h" 48 #include "dispatch.h" 49 #include "ssherr.h" 50 #include "sshbuf.h" 51 52 static int input_kex_dh_gex_request(int, u_int32_t, void *); 53 static int input_kex_dh_gex_init(int, u_int32_t, void *); 54 55 int 56 kexgex_server(struct ssh *ssh) 57 { 58 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 59 &input_kex_dh_gex_request); 60 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 61 return 0; 62 } 63 64 static int 65 input_kex_dh_gex_request(int type, u_int32_t seq, void *ctxt) 66 { 67 struct ssh *ssh = ctxt; 68 struct kex *kex = ssh->kex; 69 int r; 70 u_int min = 0, max = 0, nbits = 0; 71 72 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 73 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 74 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 75 (r = sshpkt_get_u32(ssh, &max)) != 0 || 76 (r = sshpkt_get_end(ssh)) != 0) 77 goto out; 78 kex->nbits = nbits; 79 kex->min = min; 80 kex->max = max; 81 min = MAX(DH_GRP_MIN, min); 82 max = MIN(DH_GRP_MAX, max); 83 nbits = MAX(DH_GRP_MIN, nbits); 84 nbits = MIN(DH_GRP_MAX, nbits); 85 86 if (kex->max < kex->min || kex->nbits < kex->min || 87 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 88 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 89 goto out; 90 } 91 92 /* Contact privileged parent */ 93 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 94 if (kex->dh == NULL) { 95 sshpkt_disconnect(ssh, "no matching DH grp found"); 96 r = SSH_ERR_ALLOC_FAIL; 97 goto out; 98 } 99 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 100 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 101 (r = sshpkt_put_bignum2(ssh, kex->dh->p)) != 0 || 102 (r = sshpkt_put_bignum2(ssh, kex->dh->g)) != 0 || 103 (r = sshpkt_send(ssh)) != 0) 104 goto out; 105 106 /* Compute our exchange value in parallel with the client */ 107 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 108 goto out; 109 110 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 111 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 112 r = 0; 113 out: 114 return r; 115 } 116 117 static int 118 input_kex_dh_gex_init(int type, u_int32_t seq, void *ctxt) 119 { 120 struct ssh *ssh = ctxt; 121 struct kex *kex = ssh->kex; 122 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 123 struct sshkey *server_host_public, *server_host_private; 124 u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL; 125 u_char hash[SSH_DIGEST_MAX_LENGTH]; 126 size_t sbloblen, slen; 127 size_t klen = 0, hashlen; 128 int kout, r; 129 130 if (kex->load_host_public_key == NULL || 131 kex->load_host_private_key == NULL) { 132 r = SSH_ERR_INVALID_ARGUMENT; 133 goto out; 134 } 135 server_host_public = kex->load_host_public_key(kex->hostkey_type, 136 kex->hostkey_nid, ssh); 137 server_host_private = kex->load_host_private_key(kex->hostkey_type, 138 kex->hostkey_nid, ssh); 139 if (server_host_public == NULL) { 140 r = SSH_ERR_NO_HOSTKEY_LOADED; 141 goto out; 142 } 143 144 /* key, cert */ 145 if ((dh_client_pub = BN_new()) == NULL) { 146 r = SSH_ERR_ALLOC_FAIL; 147 goto out; 148 } 149 if ((r = sshpkt_get_bignum2(ssh, dh_client_pub)) != 0 || 150 (r = sshpkt_get_end(ssh)) != 0) 151 goto out; 152 153 #ifdef DEBUG_KEXDH 154 fprintf(stderr, "dh_client_pub= "); 155 BN_print_fp(stderr, dh_client_pub); 156 fprintf(stderr, "\n"); 157 debug("bits %d", BN_num_bits(dh_client_pub)); 158 #endif 159 160 #ifdef DEBUG_KEXDH 161 DHparams_print_fp(stderr, kex->dh); 162 fprintf(stderr, "pub= "); 163 BN_print_fp(stderr, kex->dh->pub_key); 164 fprintf(stderr, "\n"); 165 #endif 166 if (!dh_pub_is_valid(kex->dh, dh_client_pub)) { 167 sshpkt_disconnect(ssh, "bad client public DH value"); 168 r = SSH_ERR_MESSAGE_INCOMPLETE; 169 goto out; 170 } 171 172 klen = DH_size(kex->dh); 173 if ((kbuf = malloc(klen)) == NULL || 174 (shared_secret = BN_new()) == NULL) { 175 r = SSH_ERR_ALLOC_FAIL; 176 goto out; 177 } 178 if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 || 179 BN_bin2bn(kbuf, kout, shared_secret) == NULL) { 180 r = SSH_ERR_LIBCRYPTO_ERROR; 181 goto out; 182 } 183 #ifdef DEBUG_KEXDH 184 dump_digest("shared secret", kbuf, kout); 185 #endif 186 if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob, 187 &sbloblen)) != 0) 188 goto out; 189 /* calc H */ 190 hashlen = sizeof(hash); 191 if ((r = kexgex_hash( 192 kex->hash_alg, 193 kex->client_version_string, 194 kex->server_version_string, 195 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer), 196 sshbuf_ptr(kex->my), sshbuf_len(kex->my), 197 server_host_key_blob, sbloblen, 198 kex->min, kex->nbits, kex->max, 199 kex->dh->p, kex->dh->g, 200 dh_client_pub, 201 kex->dh->pub_key, 202 shared_secret, 203 hash, &hashlen)) != 0) 204 goto out; 205 206 /* save session id := H */ 207 if (kex->session_id == NULL) { 208 kex->session_id_len = hashlen; 209 kex->session_id = malloc(kex->session_id_len); 210 if (kex->session_id == NULL) { 211 r = SSH_ERR_ALLOC_FAIL; 212 goto out; 213 } 214 memcpy(kex->session_id, hash, kex->session_id_len); 215 } 216 217 /* sign H */ 218 if ((r = kex->sign(server_host_private, server_host_public, &signature, 219 &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0) 220 goto out; 221 222 /* destroy_sensitive_data(); */ 223 224 /* send server hostkey, DH pubkey 'f' and singed H */ 225 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 226 (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 || 227 (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 || /* f */ 228 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 229 (r = sshpkt_send(ssh)) != 0) 230 goto out; 231 232 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0) 233 r = kex_send_newkeys(ssh); 234 out: 235 DH_free(kex->dh); 236 kex->dh = NULL; 237 if (dh_client_pub) 238 BN_clear_free(dh_client_pub); 239 if (kbuf) { 240 explicit_bzero(kbuf, klen); 241 free(kbuf); 242 } 243 if (shared_secret) 244 BN_clear_free(shared_secret); 245 free(server_host_key_blob); 246 free(signature); 247 return r; 248 } 249