1/* $OpenBSD: kexgexs.c,v 1.35 2018/10/04 00:04:41 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 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 "openbsd-compat/openssl-compat.h" 40 41#include "sshkey.h" 42#include "cipher.h" 43#include "digest.h" 44#include "kex.h" 45#include "log.h" 46#include "packet.h" 47#include "dh.h" 48#include "ssh2.h" 49#include "compat.h" 50#ifdef GSSAPI 51#include "ssh-gss.h" 52#endif 53#include "monitor_wrap.h" 54#include "dispatch.h" 55#include "ssherr.h" 56#include "sshbuf.h" 57#include "misc.h" 58 59static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *); 60static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); 61 62int 63kexgex_server(struct ssh *ssh) 64{ 65 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 66 &input_kex_dh_gex_request); 67 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 68 return 0; 69} 70 71static int 72input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) 73{ 74 struct kex *kex = ssh->kex; 75 int r; 76 u_int min = 0, max = 0, nbits = 0; 77 const BIGNUM *dh_p, *dh_g; 78 79 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 80 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 81 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 82 (r = sshpkt_get_u32(ssh, &max)) != 0 || 83 (r = sshpkt_get_end(ssh)) != 0) 84 goto out; 85 kex->nbits = nbits; 86 kex->min = min; 87 kex->max = max; 88 min = MAXIMUM(DH_GRP_MIN, min); 89 max = MINIMUM(DH_GRP_MAX, max); 90 nbits = MAXIMUM(DH_GRP_MIN, nbits); 91 nbits = MINIMUM(DH_GRP_MAX, nbits); 92 93 if (kex->max < kex->min || kex->nbits < kex->min || 94 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 95 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 96 goto out; 97 } 98 99 /* Contact privileged parent */ 100 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 101 if (kex->dh == NULL) { 102 sshpkt_disconnect(ssh, "no matching DH grp found"); 103 r = SSH_ERR_ALLOC_FAIL; 104 goto out; 105 } 106 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 107 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 108 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 109 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 || 110 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 || 111 (r = sshpkt_send(ssh)) != 0) 112 goto out; 113 114 /* Compute our exchange value in parallel with the client */ 115 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 116 goto out; 117 118 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 119 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 120 r = 0; 121 out: 122 return r; 123} 124 125static int 126input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) 127{ 128 struct kex *kex = ssh->kex; 129 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 130 const BIGNUM *pub_key, *dh_p, *dh_g; 131 struct sshkey *server_host_public, *server_host_private; 132 u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL; 133 u_char hash[SSH_DIGEST_MAX_LENGTH]; 134 size_t sbloblen, slen; 135 size_t klen = 0, hashlen; 136 int kout, r; 137 138 if (kex->load_host_public_key == NULL || 139 kex->load_host_private_key == NULL) { 140 r = SSH_ERR_INVALID_ARGUMENT; 141 goto out; 142 } 143 server_host_public = kex->load_host_public_key(kex->hostkey_type, 144 kex->hostkey_nid, ssh); 145 server_host_private = kex->load_host_private_key(kex->hostkey_type, 146 kex->hostkey_nid, ssh); 147 if (server_host_public == NULL) { 148 r = SSH_ERR_NO_HOSTKEY_LOADED; 149 goto out; 150 } 151 152 /* key, cert */ 153 if ((dh_client_pub = BN_new()) == NULL) { 154 r = SSH_ERR_ALLOC_FAIL; 155 goto out; 156 } 157 if ((r = sshpkt_get_bignum2(ssh, dh_client_pub)) != 0 || 158 (r = sshpkt_get_end(ssh)) != 0) 159 goto out; 160 161 DH_get0_key(kex->dh, &pub_key, NULL); 162 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 163 164#ifdef DEBUG_KEXDH 165 fprintf(stderr, "dh_client_pub= "); 166 BN_print_fp(stderr, dh_client_pub); 167 fprintf(stderr, "\n"); 168 debug("bits %d", BN_num_bits(dh_client_pub)); 169 DHparams_print_fp(stderr, kex->dh); 170 fprintf(stderr, "pub= "); 171 BN_print_fp(stderr, pub_key); 172 fprintf(stderr, "\n"); 173#endif 174 if (!dh_pub_is_valid(kex->dh, dh_client_pub)) { 175 sshpkt_disconnect(ssh, "bad client public DH value"); 176 r = SSH_ERR_MESSAGE_INCOMPLETE; 177 goto out; 178 } 179 180 klen = DH_size(kex->dh); 181 if ((kbuf = malloc(klen)) == NULL || 182 (shared_secret = BN_new()) == NULL) { 183 r = SSH_ERR_ALLOC_FAIL; 184 goto out; 185 } 186 if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 || 187 BN_bin2bn(kbuf, kout, shared_secret) == NULL) { 188 r = SSH_ERR_LIBCRYPTO_ERROR; 189 goto out; 190 } 191#ifdef DEBUG_KEXDH 192 dump_digest("shared secret", kbuf, kout); 193#endif 194 if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob, 195 &sbloblen)) != 0) 196 goto out; 197 /* calc H */ 198 hashlen = sizeof(hash); 199 if ((r = kexgex_hash( 200 kex->hash_alg, 201 kex->client_version_string, 202 kex->server_version_string, 203 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer), 204 sshbuf_ptr(kex->my), sshbuf_len(kex->my), 205 server_host_key_blob, sbloblen, 206 kex->min, kex->nbits, kex->max, 207 dh_p, dh_g, 208 dh_client_pub, 209 pub_key, 210 shared_secret, 211 hash, &hashlen)) != 0) 212 goto out; 213 214 /* save session id := H */ 215 if (kex->session_id == NULL) { 216 kex->session_id_len = hashlen; 217 kex->session_id = malloc(kex->session_id_len); 218 if (kex->session_id == NULL) { 219 r = SSH_ERR_ALLOC_FAIL; 220 goto out; 221 } 222 memcpy(kex->session_id, hash, kex->session_id_len); 223 } 224 225 /* sign H */ 226 if ((r = kex->sign(server_host_private, server_host_public, &signature, 227 &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0) 228 goto out; 229 230 /* destroy_sensitive_data(); */ 231 232 /* send server hostkey, DH pubkey 'f' and signed H */ 233 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 234 (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 || 235 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */ 236 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 237 (r = sshpkt_send(ssh)) != 0) 238 goto out; 239 240 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0) 241 r = kex_send_newkeys(ssh); 242 out: 243 explicit_bzero(hash, sizeof(hash)); 244 DH_free(kex->dh); 245 kex->dh = NULL; 246 BN_clear_free(dh_client_pub); 247 if (kbuf) { 248 explicit_bzero(kbuf, klen); 249 free(kbuf); 250 } 251 BN_clear_free(shared_secret); 252 free(server_host_key_blob); 253 free(signature); 254 return r; 255} 256#endif /* WITH_OPENSSL */ 257