1/* $OpenBSD: kexgexc.c,v 1.27 2018/02/07 02:06:51 jsing 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 "openbsd-compat/openssl-compat.h" 41 42#include "sshkey.h" 43#include "cipher.h" 44#include "digest.h" 45#include "kex.h" 46#include "log.h" 47#include "packet.h" 48#include "dh.h" 49#include "ssh2.h" 50#include "compat.h" 51#include "dispatch.h" 52#include "ssherr.h" 53#include "sshbuf.h" 54#include "misc.h" 55 56static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *); 57static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *); 58 59int 60kexgex_client(struct ssh *ssh) 61{ 62 struct kex *kex = ssh->kex; 63 int r; 64 u_int nbits; 65 66 nbits = dh_estimate(kex->dh_need * 8); 67 68 kex->min = DH_GRP_MIN; 69 kex->max = DH_GRP_MAX; 70 kex->nbits = nbits; 71 if (datafellows & SSH_BUG_DHGEX_LARGE) 72 kex->nbits = MINIMUM(kex->nbits, 4096); 73 /* New GEX request */ 74 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 || 75 (r = sshpkt_put_u32(ssh, kex->min)) != 0 || 76 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 || 77 (r = sshpkt_put_u32(ssh, kex->max)) != 0 || 78 (r = sshpkt_send(ssh)) != 0) 79 goto out; 80 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent", 81 kex->min, kex->nbits, kex->max); 82#ifdef DEBUG_KEXDH 83 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 84 kex->min, kex->nbits, kex->max); 85#endif 86 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, 87 &input_kex_dh_gex_group); 88 r = 0; 89 out: 90 return r; 91} 92 93static int 94input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh) 95{ 96 struct kex *kex = ssh->kex; 97 BIGNUM *p = NULL, *g = NULL; 98 const BIGNUM *pub_key; 99 int r, bits; 100 101 debug("got SSH2_MSG_KEX_DH_GEX_GROUP"); 102 103 if ((p = BN_new()) == NULL || 104 (g = BN_new()) == NULL) { 105 r = SSH_ERR_ALLOC_FAIL; 106 goto out; 107 } 108 if ((r = sshpkt_get_bignum2(ssh, p)) != 0 || 109 (r = sshpkt_get_bignum2(ssh, g)) != 0 || 110 (r = sshpkt_get_end(ssh)) != 0) 111 goto out; 112 if ((bits = BN_num_bits(p)) < 0 || 113 (u_int)bits < kex->min || (u_int)bits > kex->max) { 114 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 115 goto out; 116 } 117 if ((kex->dh = dh_new_group(g, p)) == NULL) { 118 r = SSH_ERR_ALLOC_FAIL; 119 goto out; 120 } 121 p = g = NULL; /* belong to kex->dh now */ 122 123 /* generate and send 'e', client DH public key */ 124 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 125 goto out; 126 DH_get0_key(kex->dh, &pub_key, NULL); 127 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 || 128 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || 129 (r = sshpkt_send(ssh)) != 0) 130 goto out; 131 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 132#ifdef DEBUG_KEXDH 133 DHparams_print_fp(stderr, kex->dh); 134 fprintf(stderr, "pub= "); 135 BN_print_fp(stderr, pub_key); 136 fprintf(stderr, "\n"); 137#endif 138 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL); 139 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply); 140 r = 0; 141out: 142 BN_clear_free(p); 143 BN_clear_free(g); 144 return r; 145} 146 147static int 148input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh) 149{ 150 struct kex *kex = ssh->kex; 151 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 152 const BIGNUM *pub_key, *dh_p, *dh_g; 153 struct sshkey *server_host_key = NULL; 154 u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL; 155 u_char hash[SSH_DIGEST_MAX_LENGTH]; 156 size_t klen = 0, slen, sbloblen, hashlen; 157 int kout, r; 158 159 debug("got SSH2_MSG_KEX_DH_GEX_REPLY"); 160 if (kex->verify_host_key == NULL) { 161 r = SSH_ERR_INVALID_ARGUMENT; 162 goto out; 163 } 164 /* key, cert */ 165 if ((r = sshpkt_get_string(ssh, &server_host_key_blob, 166 &sbloblen)) != 0 || 167 (r = sshkey_from_blob(server_host_key_blob, sbloblen, 168 &server_host_key)) != 0) 169 goto out; 170 if (server_host_key->type != kex->hostkey_type || 171 (kex->hostkey_type == KEY_ECDSA && 172 server_host_key->ecdsa_nid != kex->hostkey_nid)) { 173 r = SSH_ERR_KEY_TYPE_MISMATCH; 174 goto out; 175 } 176 if (kex->verify_host_key(server_host_key, ssh) == -1) { 177 r = SSH_ERR_SIGNATURE_INVALID; 178 goto out; 179 } 180 /* DH parameter f, server public DH key */ 181 if ((dh_server_pub = BN_new()) == NULL) { 182 r = SSH_ERR_ALLOC_FAIL; 183 goto out; 184 } 185 /* signed H */ 186 if ((r = sshpkt_get_bignum2(ssh, dh_server_pub)) != 0 || 187 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 188 (r = sshpkt_get_end(ssh)) != 0) 189 goto out; 190#ifdef DEBUG_KEXDH 191 fprintf(stderr, "dh_server_pub= "); 192 BN_print_fp(stderr, dh_server_pub); 193 fprintf(stderr, "\n"); 194 debug("bits %d", BN_num_bits(dh_server_pub)); 195#endif 196 if (!dh_pub_is_valid(kex->dh, dh_server_pub)) { 197 sshpkt_disconnect(ssh, "bad server public DH value"); 198 r = SSH_ERR_MESSAGE_INCOMPLETE; 199 goto out; 200 } 201 202 klen = DH_size(kex->dh); 203 if ((kbuf = malloc(klen)) == NULL || 204 (shared_secret = BN_new()) == NULL) { 205 r = SSH_ERR_ALLOC_FAIL; 206 goto out; 207 } 208 if ((kout = DH_compute_key(kbuf, dh_server_pub, kex->dh)) < 0 || 209 BN_bin2bn(kbuf, kout, shared_secret) == NULL) { 210 r = SSH_ERR_LIBCRYPTO_ERROR; 211 goto out; 212 } 213#ifdef DEBUG_KEXDH 214 dump_digest("shared secret", kbuf, kout); 215#endif 216 if (ssh->compat & SSH_OLD_DHGEX) 217 kex->min = kex->max = -1; 218 219 /* calc and verify H */ 220 DH_get0_key(kex->dh, &pub_key, NULL); 221 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 222 hashlen = sizeof(hash); 223 if ((r = kexgex_hash( 224 kex->hash_alg, 225 kex->client_version_string, 226 kex->server_version_string, 227 sshbuf_ptr(kex->my), sshbuf_len(kex->my), 228 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer), 229 server_host_key_blob, sbloblen, 230 kex->min, kex->nbits, kex->max, 231 dh_p, dh_g, 232 pub_key, 233 dh_server_pub, 234 shared_secret, 235 hash, &hashlen)) != 0) 236 goto out; 237 238 if ((r = sshkey_verify(server_host_key, signature, slen, hash, 239 hashlen, kex->hostkey_alg, ssh->compat)) != 0) 240 goto out; 241 242 /* save session id */ 243 if (kex->session_id == NULL) { 244 kex->session_id_len = hashlen; 245 kex->session_id = malloc(kex->session_id_len); 246 if (kex->session_id == NULL) { 247 r = SSH_ERR_ALLOC_FAIL; 248 goto out; 249 } 250 memcpy(kex->session_id, hash, kex->session_id_len); 251 } 252 253 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0) 254 r = kex_send_newkeys(ssh); 255 out: 256 explicit_bzero(hash, sizeof(hash)); 257 DH_free(kex->dh); 258 kex->dh = NULL; 259 BN_clear_free(dh_server_pub); 260 if (kbuf) { 261 explicit_bzero(kbuf, klen); 262 free(kbuf); 263 } 264 BN_clear_free(shared_secret); 265 sshkey_free(server_host_key); 266 free(server_host_key_blob); 267 free(signature); 268 return r; 269} 270#endif /* WITH_OPENSSL */ 271