1 /* $OpenBSD: kexgexc.c,v 1.25 2017/05/30 14:23:52 markus 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 #include "misc.h" 53 54 static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *); 55 static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *); 56 57 int 58 kexgex_client(struct ssh *ssh) 59 { 60 struct kex *kex = ssh->kex; 61 int r; 62 u_int nbits; 63 64 nbits = dh_estimate(kex->dh_need * 8); 65 66 kex->min = DH_GRP_MIN; 67 kex->max = DH_GRP_MAX; 68 kex->nbits = nbits; 69 if (datafellows & SSH_BUG_DHGEX_LARGE) 70 kex->nbits = MINIMUM(kex->nbits, 4096); 71 /* New GEX request */ 72 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 || 73 (r = sshpkt_put_u32(ssh, kex->min)) != 0 || 74 (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 || 75 (r = sshpkt_put_u32(ssh, kex->max)) != 0 || 76 (r = sshpkt_send(ssh)) != 0) 77 goto out; 78 debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent", 79 kex->min, kex->nbits, kex->max); 80 #ifdef DEBUG_KEXDH 81 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", 82 kex->min, kex->nbits, kex->max); 83 #endif 84 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, 85 &input_kex_dh_gex_group); 86 r = 0; 87 out: 88 return r; 89 } 90 91 static int 92 input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh) 93 { 94 struct kex *kex = ssh->kex; 95 BIGNUM *p = NULL, *g = NULL; 96 int r, bits; 97 98 debug("got SSH2_MSG_KEX_DH_GEX_GROUP"); 99 100 if ((p = BN_new()) == NULL || 101 (g = BN_new()) == NULL) { 102 r = SSH_ERR_ALLOC_FAIL; 103 goto out; 104 } 105 if ((r = sshpkt_get_bignum2(ssh, p)) != 0 || 106 (r = sshpkt_get_bignum2(ssh, g)) != 0 || 107 (r = sshpkt_get_end(ssh)) != 0) 108 goto out; 109 if ((bits = BN_num_bits(p)) < 0 || 110 (u_int)bits < kex->min || (u_int)bits > kex->max) { 111 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 112 goto out; 113 } 114 if ((kex->dh = dh_new_group(g, p)) == NULL) { 115 r = SSH_ERR_ALLOC_FAIL; 116 goto out; 117 } 118 p = g = NULL; /* belong to kex->dh now */ 119 120 /* generate and send 'e', client DH public key */ 121 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0 || 122 (r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 || 123 (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 || 124 (r = sshpkt_send(ssh)) != 0) 125 goto out; 126 debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); 127 #ifdef DEBUG_KEXDH 128 DHparams_print_fp(stderr, kex->dh); 129 fprintf(stderr, "pub= "); 130 BN_print_fp(stderr, kex->dh->pub_key); 131 fprintf(stderr, "\n"); 132 #endif 133 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, NULL); 134 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply); 135 r = 0; 136 out: 137 if (p) 138 BN_clear_free(p); 139 if (g) 140 BN_clear_free(g); 141 return r; 142 } 143 144 static int 145 input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh) 146 { 147 struct kex *kex = ssh->kex; 148 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; 149 struct sshkey *server_host_key = NULL; 150 u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL; 151 u_char hash[SSH_DIGEST_MAX_LENGTH]; 152 size_t klen = 0, slen, sbloblen, hashlen; 153 int kout, r; 154 155 debug("got SSH2_MSG_KEX_DH_GEX_REPLY"); 156 if (kex->verify_host_key == NULL) { 157 r = SSH_ERR_INVALID_ARGUMENT; 158 goto out; 159 } 160 /* key, cert */ 161 if ((r = sshpkt_get_string(ssh, &server_host_key_blob, 162 &sbloblen)) != 0 || 163 (r = sshkey_from_blob(server_host_key_blob, sbloblen, 164 &server_host_key)) != 0) 165 goto out; 166 if (server_host_key->type != kex->hostkey_type || 167 (kex->hostkey_type == KEY_ECDSA && 168 server_host_key->ecdsa_nid != kex->hostkey_nid)) { 169 r = SSH_ERR_KEY_TYPE_MISMATCH; 170 goto out; 171 } 172 if (kex->verify_host_key(server_host_key, ssh) == -1) { 173 r = SSH_ERR_SIGNATURE_INVALID; 174 goto out; 175 } 176 /* DH parameter f, server public DH key */ 177 if ((dh_server_pub = BN_new()) == NULL) { 178 r = SSH_ERR_ALLOC_FAIL; 179 goto out; 180 } 181 /* signed H */ 182 if ((r = sshpkt_get_bignum2(ssh, dh_server_pub)) != 0 || 183 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 184 (r = sshpkt_get_end(ssh)) != 0) 185 goto out; 186 #ifdef DEBUG_KEXDH 187 fprintf(stderr, "dh_server_pub= "); 188 BN_print_fp(stderr, dh_server_pub); 189 fprintf(stderr, "\n"); 190 debug("bits %d", BN_num_bits(dh_server_pub)); 191 #endif 192 if (!dh_pub_is_valid(kex->dh, dh_server_pub)) { 193 sshpkt_disconnect(ssh, "bad server public DH value"); 194 r = SSH_ERR_MESSAGE_INCOMPLETE; 195 goto out; 196 } 197 198 klen = DH_size(kex->dh); 199 if ((kbuf = malloc(klen)) == NULL || 200 (shared_secret = BN_new()) == NULL) { 201 r = SSH_ERR_ALLOC_FAIL; 202 goto out; 203 } 204 if ((kout = DH_compute_key(kbuf, dh_server_pub, kex->dh)) < 0 || 205 BN_bin2bn(kbuf, kout, shared_secret) == NULL) { 206 r = SSH_ERR_LIBCRYPTO_ERROR; 207 goto out; 208 } 209 #ifdef DEBUG_KEXDH 210 dump_digest("shared secret", kbuf, kout); 211 #endif 212 if (ssh->compat & SSH_OLD_DHGEX) 213 kex->min = kex->max = -1; 214 215 /* calc and verify H */ 216 hashlen = sizeof(hash); 217 if ((r = kexgex_hash( 218 kex->hash_alg, 219 kex->client_version_string, 220 kex->server_version_string, 221 sshbuf_ptr(kex->my), sshbuf_len(kex->my), 222 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer), 223 server_host_key_blob, sbloblen, 224 kex->min, kex->nbits, kex->max, 225 kex->dh->p, kex->dh->g, 226 kex->dh->pub_key, 227 dh_server_pub, 228 shared_secret, 229 hash, &hashlen)) != 0) 230 goto out; 231 232 if ((r = sshkey_verify(server_host_key, signature, slen, hash, 233 hashlen, ssh->compat)) != 0) 234 goto out; 235 236 /* save session id */ 237 if (kex->session_id == NULL) { 238 kex->session_id_len = hashlen; 239 kex->session_id = malloc(kex->session_id_len); 240 if (kex->session_id == NULL) { 241 r = SSH_ERR_ALLOC_FAIL; 242 goto out; 243 } 244 memcpy(kex->session_id, hash, kex->session_id_len); 245 } 246 247 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0) 248 r = kex_send_newkeys(ssh); 249 out: 250 explicit_bzero(hash, sizeof(hash)); 251 DH_free(kex->dh); 252 kex->dh = NULL; 253 if (dh_server_pub) 254 BN_clear_free(dh_server_pub); 255 if (kbuf) { 256 explicit_bzero(kbuf, klen); 257 free(kbuf); 258 } 259 if (shared_secret) 260 BN_clear_free(shared_secret); 261 sshkey_free(server_host_key); 262 free(server_host_key_blob); 263 free(signature); 264 return r; 265 } 266 #endif /* WITH_OPENSSL */ 267