1 /* $OpenBSD: kexgen.c,v 1.4 2019/11/25 00:51:37 djm Exp $ */ 2 /* 3 * Copyright (c) 2019 Markus Friedl. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26 #include "includes.h" 27 28 #include <sys/types.h> 29 30 #include <stdarg.h> 31 #include <stdio.h> 32 #include <string.h> 33 #include <signal.h> 34 35 #include "sshkey.h" 36 #include "kex.h" 37 #include "log.h" 38 #include "packet.h" 39 #include "ssh2.h" 40 #include "sshbuf.h" 41 #include "digest.h" 42 #include "ssherr.h" 43 44 static int input_kex_gen_init(int, u_int32_t, struct ssh *); 45 static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh); 46 47 static int 48 kex_gen_hash( 49 int hash_alg, 50 const struct sshbuf *client_version, 51 const struct sshbuf *server_version, 52 const struct sshbuf *client_kexinit, 53 const struct sshbuf *server_kexinit, 54 const struct sshbuf *server_host_key_blob, 55 const struct sshbuf *client_pub, 56 const struct sshbuf *server_pub, 57 const struct sshbuf *shared_secret, 58 u_char *hash, size_t *hashlen) 59 { 60 struct sshbuf *b; 61 int r; 62 63 if (*hashlen < ssh_digest_bytes(hash_alg)) 64 return SSH_ERR_INVALID_ARGUMENT; 65 if ((b = sshbuf_new()) == NULL) 66 return SSH_ERR_ALLOC_FAIL; 67 if ((r = sshbuf_put_stringb(b, client_version)) != 0 || 68 (r = sshbuf_put_stringb(b, server_version)) != 0 || 69 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ 70 (r = sshbuf_put_u32(b, sshbuf_len(client_kexinit) + 1)) != 0 || 71 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 || 72 (r = sshbuf_putb(b, client_kexinit)) != 0 || 73 (r = sshbuf_put_u32(b, sshbuf_len(server_kexinit) + 1)) != 0 || 74 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 || 75 (r = sshbuf_putb(b, server_kexinit)) != 0 || 76 (r = sshbuf_put_stringb(b, server_host_key_blob)) != 0 || 77 (r = sshbuf_put_stringb(b, client_pub)) != 0 || 78 (r = sshbuf_put_stringb(b, server_pub)) != 0 || 79 (r = sshbuf_putb(b, shared_secret)) != 0) { 80 sshbuf_free(b); 81 return r; 82 } 83 #ifdef DEBUG_KEX 84 sshbuf_dump(b, stderr); 85 #endif 86 if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) { 87 sshbuf_free(b); 88 return SSH_ERR_LIBCRYPTO_ERROR; 89 } 90 sshbuf_free(b); 91 *hashlen = ssh_digest_bytes(hash_alg); 92 #ifdef DEBUG_KEX 93 dump_digest("hash", hash, *hashlen); 94 #endif 95 return 0; 96 } 97 98 int 99 kex_gen_client(struct ssh *ssh) 100 { 101 struct kex *kex = ssh->kex; 102 int r; 103 104 switch (kex->kex_type) { 105 #ifdef WITH_OPENSSL 106 case KEX_DH_GRP1_SHA1: 107 case KEX_DH_GRP14_SHA1: 108 case KEX_DH_GRP14_SHA256: 109 case KEX_DH_GRP16_SHA512: 110 case KEX_DH_GRP18_SHA512: 111 r = kex_dh_keypair(kex); 112 break; 113 case KEX_ECDH_SHA2: 114 r = kex_ecdh_keypair(kex); 115 break; 116 #endif 117 case KEX_C25519_SHA256: 118 r = kex_c25519_keypair(kex); 119 break; 120 case KEX_KEM_SNTRUP4591761X25519_SHA512: 121 r = kex_kem_sntrup4591761x25519_keypair(kex); 122 break; 123 default: 124 r = SSH_ERR_INVALID_ARGUMENT; 125 break; 126 } 127 if (r != 0) 128 return r; 129 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 || 130 (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 || 131 (r = sshpkt_send(ssh)) != 0) 132 return r; 133 debug("expecting SSH2_MSG_KEX_ECDH_REPLY"); 134 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply); 135 return 0; 136 } 137 138 static int 139 input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh) 140 { 141 struct kex *kex = ssh->kex; 142 struct sshkey *server_host_key = NULL; 143 struct sshbuf *shared_secret = NULL; 144 struct sshbuf *server_blob = NULL; 145 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL; 146 u_char *signature = NULL; 147 u_char hash[SSH_DIGEST_MAX_LENGTH]; 148 size_t slen, hashlen; 149 int r; 150 151 /* hostkey */ 152 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) 153 goto out; 154 /* sshkey_fromb() consumes its buffer, so make a copy */ 155 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { 156 r = SSH_ERR_ALLOC_FAIL; 157 goto out; 158 } 159 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0) 160 goto out; 161 if ((r = kex_verify_host_key(ssh, server_host_key)) != 0) 162 goto out; 163 164 /* Q_S, server public key */ 165 /* signed H */ 166 if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 || 167 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 168 (r = sshpkt_get_end(ssh)) != 0) 169 goto out; 170 171 /* compute shared secret */ 172 switch (kex->kex_type) { 173 #ifdef WITH_OPENSSL 174 case KEX_DH_GRP1_SHA1: 175 case KEX_DH_GRP14_SHA1: 176 case KEX_DH_GRP14_SHA256: 177 case KEX_DH_GRP16_SHA512: 178 case KEX_DH_GRP18_SHA512: 179 r = kex_dh_dec(kex, server_blob, &shared_secret); 180 break; 181 case KEX_ECDH_SHA2: 182 r = kex_ecdh_dec(kex, server_blob, &shared_secret); 183 break; 184 #endif 185 case KEX_C25519_SHA256: 186 r = kex_c25519_dec(kex, server_blob, &shared_secret); 187 break; 188 case KEX_KEM_SNTRUP4591761X25519_SHA512: 189 r = kex_kem_sntrup4591761x25519_dec(kex, server_blob, 190 &shared_secret); 191 break; 192 default: 193 r = SSH_ERR_INVALID_ARGUMENT; 194 break; 195 } 196 if (r !=0 ) 197 goto out; 198 199 /* calc and verify H */ 200 hashlen = sizeof(hash); 201 if ((r = kex_gen_hash( 202 kex->hash_alg, 203 kex->client_version, 204 kex->server_version, 205 kex->my, 206 kex->peer, 207 server_host_key_blob, 208 kex->client_pub, 209 server_blob, 210 shared_secret, 211 hash, &hashlen)) != 0) 212 goto out; 213 214 if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen, 215 kex->hostkey_alg, ssh->compat, NULL)) != 0) 216 goto out; 217 218 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 219 r = kex_send_newkeys(ssh); 220 out: 221 explicit_bzero(hash, sizeof(hash)); 222 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 223 explicit_bzero(kex->sntrup4591761_client_key, 224 sizeof(kex->sntrup4591761_client_key)); 225 sshbuf_free(server_host_key_blob); 226 free(signature); 227 sshbuf_free(tmp); 228 sshkey_free(server_host_key); 229 sshbuf_free(server_blob); 230 sshbuf_free(shared_secret); 231 sshbuf_free(kex->client_pub); 232 kex->client_pub = NULL; 233 return r; 234 } 235 236 int 237 kex_gen_server(struct ssh *ssh) 238 { 239 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 240 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); 241 return 0; 242 } 243 244 static int 245 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) 246 { 247 struct kex *kex = ssh->kex; 248 struct sshkey *server_host_private, *server_host_public; 249 struct sshbuf *shared_secret = NULL; 250 struct sshbuf *server_pubkey = NULL; 251 struct sshbuf *client_pubkey = NULL; 252 struct sshbuf *server_host_key_blob = NULL; 253 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; 254 size_t slen, hashlen; 255 int r; 256 257 if ((r = kex_load_hostkey(ssh, &server_host_private, 258 &server_host_public)) != 0) 259 goto out; 260 261 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 262 (r = sshpkt_get_end(ssh)) != 0) 263 goto out; 264 265 /* compute shared secret */ 266 switch (kex->kex_type) { 267 #ifdef WITH_OPENSSL 268 case KEX_DH_GRP1_SHA1: 269 case KEX_DH_GRP14_SHA1: 270 case KEX_DH_GRP14_SHA256: 271 case KEX_DH_GRP16_SHA512: 272 case KEX_DH_GRP18_SHA512: 273 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 274 &shared_secret); 275 break; 276 case KEX_ECDH_SHA2: 277 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 278 &shared_secret); 279 break; 280 #endif 281 case KEX_C25519_SHA256: 282 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 283 &shared_secret); 284 break; 285 case KEX_KEM_SNTRUP4591761X25519_SHA512: 286 r = kex_kem_sntrup4591761x25519_enc(kex, client_pubkey, 287 &server_pubkey, &shared_secret); 288 break; 289 default: 290 r = SSH_ERR_INVALID_ARGUMENT; 291 break; 292 } 293 if (r !=0 ) 294 goto out; 295 296 /* calc H */ 297 if ((server_host_key_blob = sshbuf_new()) == NULL) { 298 r = SSH_ERR_ALLOC_FAIL; 299 goto out; 300 } 301 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 302 goto out; 303 hashlen = sizeof(hash); 304 if ((r = kex_gen_hash( 305 kex->hash_alg, 306 kex->client_version, 307 kex->server_version, 308 kex->peer, 309 kex->my, 310 server_host_key_blob, 311 client_pubkey, 312 server_pubkey, 313 shared_secret, 314 hash, &hashlen)) != 0) 315 goto out; 316 317 /* sign H */ 318 if ((r = kex->sign(ssh, server_host_private, server_host_public, 319 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 320 goto out; 321 322 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 323 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 324 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 325 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 326 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 327 (r = sshpkt_send(ssh)) != 0) 328 goto out; 329 330 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 331 r = kex_send_newkeys(ssh); 332 out: 333 explicit_bzero(hash, sizeof(hash)); 334 sshbuf_free(server_host_key_blob); 335 free(signature); 336 sshbuf_free(shared_secret); 337 sshbuf_free(client_pubkey); 338 sshbuf_free(server_pubkey); 339 return r; 340 } 341