1 /* $OpenBSD: kexgexs.c,v 1.30 2016/09/12 01:22:38 deraadt 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 "includes.h" 28 29 #ifdef WITH_OPENSSL 30 31 32 #include <stdarg.h> 33 #include <stdio.h> 34 #include <string.h> 35 #include <signal.h> 36 37 #include <openssl/dh.h> 38 39 #include "sshkey.h" 40 #include "cipher.h" 41 #include "digest.h" 42 #include "kex.h" 43 #include "log.h" 44 #include "packet.h" 45 #include "dh.h" 46 #include "ssh2.h" 47 #include "compat.h" 48 #ifdef GSSAPI 49 #include "ssh-gss.h" 50 #endif 51 #include "monitor_wrap.h" 52 #include "dispatch.h" 53 #include "ssherr.h" 54 #include "sshbuf.h" 55 #include "misc.h" 56 57 static int input_kex_dh_gex_request(int, u_int32_t, void *); 58 static int input_kex_dh_gex_init(int, u_int32_t, void *); 59 60 int 61 kexgex_server(struct ssh *ssh) 62 { 63 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 64 &input_kex_dh_gex_request); 65 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 66 return 0; 67 } 68 69 static int 70 input_kex_dh_gex_request(int type, u_int32_t seq, void *ctxt) 71 { 72 struct ssh *ssh = ctxt; 73 struct kex *kex = ssh->kex; 74 int r; 75 u_int min = 0, max = 0, nbits = 0; 76 77 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 78 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 79 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 80 (r = sshpkt_get_u32(ssh, &max)) != 0 || 81 (r = sshpkt_get_end(ssh)) != 0) 82 goto out; 83 kex->nbits = nbits; 84 kex->min = min; 85 kex->max = max; 86 min = MAXIMUM(DH_GRP_MIN, min); 87 max = MINIMUM(DH_GRP_MAX, max); 88 nbits = MAXIMUM(DH_GRP_MIN, nbits); 89 nbits = MINIMUM(DH_GRP_MAX, nbits); 90 91 if (kex->max < kex->min || kex->nbits < kex->min || 92 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 93 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 94 goto out; 95 } 96 97 /* Contact privileged parent */ 98 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 99 if (kex->dh == NULL) { 100 sshpkt_disconnect(ssh, "no matching DH grp found"); 101 r = SSH_ERR_ALLOC_FAIL; 102 goto out; 103 } 104 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 105 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 106 (r = sshpkt_put_bignum2(ssh, kex->dh->p)) != 0 || 107 (r = sshpkt_put_bignum2(ssh, kex->dh->g)) != 0 || 108 (r = sshpkt_send(ssh)) != 0) 109 goto out; 110 111 /* Compute our exchange value in parallel with the client */ 112 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 113 goto out; 114 115 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 116 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 117 r = 0; 118 out: 119 return r; 120 } 121 122 static int 123 input_kex_dh_gex_init(int type, u_int32_t seq, void *ctxt) 124 { 125 struct ssh *ssh = ctxt; 126 struct kex *kex = ssh->kex; 127 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 128 struct sshkey *server_host_public, *server_host_private; 129 u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL; 130 u_char hash[SSH_DIGEST_MAX_LENGTH]; 131 size_t sbloblen, slen; 132 size_t klen = 0, hashlen; 133 int kout, r; 134 135 if (kex->load_host_public_key == NULL || 136 kex->load_host_private_key == NULL) { 137 r = SSH_ERR_INVALID_ARGUMENT; 138 goto out; 139 } 140 server_host_public = kex->load_host_public_key(kex->hostkey_type, 141 kex->hostkey_nid, ssh); 142 server_host_private = kex->load_host_private_key(kex->hostkey_type, 143 kex->hostkey_nid, ssh); 144 if (server_host_public == NULL) { 145 r = SSH_ERR_NO_HOSTKEY_LOADED; 146 goto out; 147 } 148 149 /* key, cert */ 150 if ((dh_client_pub = BN_new()) == NULL) { 151 r = SSH_ERR_ALLOC_FAIL; 152 goto out; 153 } 154 if ((r = sshpkt_get_bignum2(ssh, dh_client_pub)) != 0 || 155 (r = sshpkt_get_end(ssh)) != 0) 156 goto out; 157 158 #ifdef DEBUG_KEXDH 159 fprintf(stderr, "dh_client_pub= "); 160 BN_print_fp(stderr, dh_client_pub); 161 fprintf(stderr, "\n"); 162 debug("bits %d", BN_num_bits(dh_client_pub)); 163 #endif 164 165 #ifdef DEBUG_KEXDH 166 DHparams_print_fp(stderr, kex->dh); 167 fprintf(stderr, "pub= "); 168 BN_print_fp(stderr, kex->dh->pub_key); 169 fprintf(stderr, "\n"); 170 #endif 171 if (!dh_pub_is_valid(kex->dh, dh_client_pub)) { 172 sshpkt_disconnect(ssh, "bad client public DH value"); 173 r = SSH_ERR_MESSAGE_INCOMPLETE; 174 goto out; 175 } 176 177 klen = DH_size(kex->dh); 178 if ((kbuf = malloc(klen)) == NULL || 179 (shared_secret = BN_new()) == NULL) { 180 r = SSH_ERR_ALLOC_FAIL; 181 goto out; 182 } 183 if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 || 184 BN_bin2bn(kbuf, kout, shared_secret) == NULL) { 185 r = SSH_ERR_LIBCRYPTO_ERROR; 186 goto out; 187 } 188 #ifdef DEBUG_KEXDH 189 dump_digest("shared secret", kbuf, kout); 190 #endif 191 if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob, 192 &sbloblen)) != 0) 193 goto out; 194 /* calc H */ 195 hashlen = sizeof(hash); 196 if ((r = kexgex_hash( 197 kex->hash_alg, 198 kex->client_version_string, 199 kex->server_version_string, 200 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer), 201 sshbuf_ptr(kex->my), sshbuf_len(kex->my), 202 server_host_key_blob, sbloblen, 203 kex->min, kex->nbits, kex->max, 204 kex->dh->p, kex->dh->g, 205 dh_client_pub, 206 kex->dh->pub_key, 207 shared_secret, 208 hash, &hashlen)) != 0) 209 goto out; 210 211 /* save session id := H */ 212 if (kex->session_id == NULL) { 213 kex->session_id_len = hashlen; 214 kex->session_id = malloc(kex->session_id_len); 215 if (kex->session_id == NULL) { 216 r = SSH_ERR_ALLOC_FAIL; 217 goto out; 218 } 219 memcpy(kex->session_id, hash, kex->session_id_len); 220 } 221 222 /* sign H */ 223 if ((r = kex->sign(server_host_private, server_host_public, &signature, 224 &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0) 225 goto out; 226 227 /* destroy_sensitive_data(); */ 228 229 /* send server hostkey, DH pubkey 'f' and singed H */ 230 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 231 (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 || 232 (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 || /* f */ 233 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 234 (r = sshpkt_send(ssh)) != 0) 235 goto out; 236 237 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0) 238 r = kex_send_newkeys(ssh); 239 out: 240 DH_free(kex->dh); 241 kex->dh = NULL; 242 if (dh_client_pub) 243 BN_clear_free(dh_client_pub); 244 if (kbuf) { 245 explicit_bzero(kbuf, klen); 246 free(kbuf); 247 } 248 if (shared_secret) 249 BN_clear_free(shared_secret); 250 free(server_host_key_blob); 251 free(signature); 252 return r; 253 } 254 #endif /* WITH_OPENSSL */ 255
