1 /* $OpenBSD: kexgexc.c,v 1.20 2015/01/26 06:10:03 djm 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 #include <sys/types.h> 32 33 #include <openssl/dh.h> 34 35 #include <stdarg.h> 36 #include <stdio.h> 37 #include <string.h> 38 #include <signal.h> 39 40 #include "sshkey.h" 41 #include "cipher.h" 42 #include "digest.h" 43 #include "kex.h" 44 #include "log.h" 45 #include "packet.h" 46 #include "dh.h" 47 #include "ssh2.h" 48 #include "compat.h" 49 #include "dispatch.h" 50 #include "ssherr.h" 51 #include "sshbuf.h" 52 53 static int input_kex_dh_gex_group(int, u_int32_t, void *); 54 static int input_kex_dh_gex_reply(int, u_int32_t, void *); 55 56 int 57 kexgex_client(struct ssh *ssh) 58 { 59 struct kex *kex = ssh->kex; 60 int r; 61 u_int nbits; 62 63 nbits = dh_estimate(kex->dh_need * 8); 64 65 kex->min = DH_GRP_MIN; 66 kex->max = DH_GRP_MAX; 67 kex->nbits = nbits; 68 if (ssh->compat & SSH_OLD_DHGEX) { 69 /* Old GEX request */ 70 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)) 71 != 0 || 72 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 || 73 (r = sshpkt_send(ssh)) != 0) 74 goto out; 75 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", kex->nbits); 76 } else { 77 /* New GEX request */ 78 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 || 79 (r = sshpkt_put_u32(ssh, kex->min)) != 0 || 80 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 || 81 (r = sshpkt_put_u32(ssh, kex->max)) != 0 || 82 (r = sshpkt_send(ssh)) != 0) 83 goto out; 84 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent", 85 kex->min, kex->nbits, kex->max); 86 } 87 #ifdef DEBUG_KEXDH 88 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 89 kex->min, kex->nbits, kex->max); 90 #endif 91 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, 92 &input_kex_dh_gex_group); 93 r = 0; 94 out: 95 return r; 96 } 97 98 static int 99 input_kex_dh_gex_group(int type, u_int32_t seq, void *ctxt) 100 { 101 struct ssh *ssh = ctxt; 102 struct kex *kex = ssh->kex; 103 BIGNUM *p = NULL, *g = NULL; 104 int r, bits; 105 106 debug("got SSH2_MSG_KEX_DH_GEX_GROUP"); 107 108 if ((p = BN_new()) == NULL || 109 (g = BN_new()) == NULL) { 110 r = SSH_ERR_ALLOC_FAIL; 111 goto out; 112 } 113 if ((r = sshpkt_get_bignum2(ssh, p)) != 0 || 114 (r = sshpkt_get_bignum2(ssh, g)) != 0 || 115 (r = sshpkt_get_end(ssh)) != 0) 116 goto out; 117 if ((bits = BN_num_bits(p)) < 0 || 118 (u_int)bits < kex->min || (u_int)bits > kex->max) { 119 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 120 goto out; 121 } 122 if ((kex->dh = dh_new_group(g, p)) == NULL) { 123 r = SSH_ERR_ALLOC_FAIL; 124 goto out; 125 } 126 p = g = NULL; /* belong to kex->dh now */ 127 128 /* generate and send 'e', client DH public key */ 129 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0 || 130 (r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 || 131 (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 || 132 (r = sshpkt_send(ssh)) != 0) 133 goto out; 134 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 135 #ifdef DEBUG_KEXDH 136 DHparams_print_fp(stderr, kex->dh); 137 fprintf(stderr, "pub= "); 138 BN_print_fp(stderr, kex->dh->pub_key); 139 fprintf(stderr, "\n"); 140 #endif 141 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL); 142 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply); 143 r = 0; 144 out: 145 if (p) 146 BN_clear_free(p); 147 if (g) 148 BN_clear_free(g); 149 return r; 150 } 151 152 static int 153 input_kex_dh_gex_reply(int type, u_int32_t seq, void *ctxt) 154 { 155 struct ssh *ssh = ctxt; 156 struct kex *kex = ssh->kex; 157 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 158 struct sshkey *server_host_key = NULL; 159 u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL; 160 u_char hash[SSH_DIGEST_MAX_LENGTH]; 161 size_t klen = 0, slen, sbloblen, hashlen; 162 int kout, r; 163 164 debug("got SSH2_MSG_KEX_DH_GEX_REPLY"); 165 if (kex->verify_host_key == NULL) { 166 r = SSH_ERR_INVALID_ARGUMENT; 167 goto out; 168 } 169 /* key, cert */ 170 if ((r = sshpkt_get_string(ssh, &server_host_key_blob, 171 &sbloblen)) != 0 || 172 (r = sshkey_from_blob(server_host_key_blob, sbloblen, 173 &server_host_key)) != 0) 174 goto out; 175 if (server_host_key->type != kex->hostkey_type) { 176 r = SSH_ERR_KEY_TYPE_MISMATCH; 177 goto out; 178 } 179 if (server_host_key->type != kex->hostkey_type || 180 (kex->hostkey_type == KEY_ECDSA && 181 server_host_key->ecdsa_nid != kex->hostkey_nid)) { 182 r = SSH_ERR_KEY_TYPE_MISMATCH; 183 goto out; 184 } 185 if (kex->verify_host_key(server_host_key, ssh) == -1) { 186 r = SSH_ERR_SIGNATURE_INVALID; 187 goto out; 188 } 189 /* DH parameter f, server public DH key */ 190 if ((dh_server_pub = BN_new()) == NULL) { 191 r = SSH_ERR_ALLOC_FAIL; 192 goto out; 193 } 194 /* signed H */ 195 if ((r = sshpkt_get_bignum2(ssh, dh_server_pub)) != 0 || 196 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 197 (r = sshpkt_get_end(ssh)) != 0) 198 goto out; 199 #ifdef DEBUG_KEXDH 200 fprintf(stderr, "dh_server_pub= "); 201 BN_print_fp(stderr, dh_server_pub); 202 fprintf(stderr, "\n"); 203 debug("bits %d", BN_num_bits(dh_server_pub)); 204 #endif 205 if (!dh_pub_is_valid(kex->dh, dh_server_pub)) { 206 sshpkt_disconnect(ssh, "bad server public DH value"); 207 r = SSH_ERR_MESSAGE_INCOMPLETE; 208 goto out; 209 } 210 211 klen = DH_size(kex->dh); 212 if ((kbuf = malloc(klen)) == NULL || 213 (shared_secret = BN_new()) == NULL) { 214 r = SSH_ERR_ALLOC_FAIL; 215 goto out; 216 } 217 if ((kout = DH_compute_key(kbuf, dh_server_pub, kex->dh)) < 0 || 218 BN_bin2bn(kbuf, kout, shared_secret) == NULL) { 219 r = SSH_ERR_LIBCRYPTO_ERROR; 220 goto out; 221 } 222 #ifdef DEBUG_KEXDH 223 dump_digest("shared secret", kbuf, kout); 224 #endif 225 if (ssh->compat & SSH_OLD_DHGEX) 226 kex->min = kex->max = -1; 227 228 /* calc and verify H */ 229 hashlen = sizeof(hash); 230 if ((r = kexgex_hash( 231 kex->hash_alg, 232 kex->client_version_string, 233 kex->server_version_string, 234 sshbuf_ptr(kex->my), sshbuf_len(kex->my), 235 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer), 236 server_host_key_blob, sbloblen, 237 kex->min, kex->nbits, kex->max, 238 kex->dh->p, kex->dh->g, 239 kex->dh->pub_key, 240 dh_server_pub, 241 shared_secret, 242 hash, &hashlen)) != 0) 243 goto out; 244 245 if ((r = sshkey_verify(server_host_key, signature, slen, hash, 246 hashlen, ssh->compat)) != 0) 247 goto out; 248 249 /* save session id */ 250 if (kex->session_id == NULL) { 251 kex->session_id_len = hashlen; 252 kex->session_id = malloc(kex->session_id_len); 253 if (kex->session_id == NULL) { 254 r = SSH_ERR_ALLOC_FAIL; 255 goto out; 256 } 257 memcpy(kex->session_id, hash, kex->session_id_len); 258 } 259 260 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0) 261 r = kex_send_newkeys(ssh); 262 out: 263 explicit_bzero(hash, sizeof(hash)); 264 DH_free(kex->dh); 265 kex->dh = NULL; 266 if (dh_server_pub) 267 BN_clear_free(dh_server_pub); 268 if (kbuf) { 269 explicit_bzero(kbuf, klen); 270 free(kbuf); 271 } 272 if (shared_secret) 273 BN_clear_free(shared_secret); 274 sshkey_free(server_host_key); 275 free(server_host_key_blob); 276 free(signature); 277 return r; 278 } 279 #endif /* WITH_OPENSSL */ 280