1/* $OpenBSD: kexgen.c,v 1.8 2021/12/19 22:08:06 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 44static int input_kex_gen_init(int, u_int32_t, struct ssh *); 45static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh); 46 47static int 48kex_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 98int 99kex_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_SNTRUP761X25519_SHA512: 121 r = kex_kem_sntrup761x25519_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 138static int 139input_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 debug("SSH2_MSG_KEX_ECDH_REPLY received"); 152 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &kex_protocol_error); 153 154 /* hostkey */ 155 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) 156 goto out; 157 /* sshkey_fromb() consumes its buffer, so make a copy */ 158 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { 159 r = SSH_ERR_ALLOC_FAIL; 160 goto out; 161 } 162 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0) 163 goto out; 164 if ((r = kex_verify_host_key(ssh, server_host_key)) != 0) 165 goto out; 166 167 /* Q_S, server public key */ 168 /* signed H */ 169 if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 || 170 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 171 (r = sshpkt_get_end(ssh)) != 0) 172 goto out; 173 174 /* compute shared secret */ 175 switch (kex->kex_type) { 176#ifdef WITH_OPENSSL 177 case KEX_DH_GRP1_SHA1: 178 case KEX_DH_GRP14_SHA1: 179 case KEX_DH_GRP14_SHA256: 180 case KEX_DH_GRP16_SHA512: 181 case KEX_DH_GRP18_SHA512: 182 r = kex_dh_dec(kex, server_blob, &shared_secret); 183 break; 184 case KEX_ECDH_SHA2: 185 r = kex_ecdh_dec(kex, server_blob, &shared_secret); 186 break; 187#endif 188 case KEX_C25519_SHA256: 189 r = kex_c25519_dec(kex, server_blob, &shared_secret); 190 break; 191 case KEX_KEM_SNTRUP761X25519_SHA512: 192 r = kex_kem_sntrup761x25519_dec(kex, server_blob, 193 &shared_secret); 194 break; 195 default: 196 r = SSH_ERR_INVALID_ARGUMENT; 197 break; 198 } 199 if (r !=0 ) 200 goto out; 201 202 /* calc and verify H */ 203 hashlen = sizeof(hash); 204 if ((r = kex_gen_hash( 205 kex->hash_alg, 206 kex->client_version, 207 kex->server_version, 208 kex->my, 209 kex->peer, 210 server_host_key_blob, 211 kex->client_pub, 212 server_blob, 213 shared_secret, 214 hash, &hashlen)) != 0) 215 goto out; 216 217 if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen, 218 kex->hostkey_alg, ssh->compat, NULL)) != 0) 219 goto out; 220 221 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 222 (r = kex_send_newkeys(ssh)) != 0) 223 goto out; 224 225 /* save initial signature and hostkey */ 226 if ((kex->flags & KEX_INITIAL) != 0) { 227 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) { 228 r = SSH_ERR_INTERNAL_ERROR; 229 goto out; 230 } 231 if ((kex->initial_sig = sshbuf_new()) == NULL) { 232 r = SSH_ERR_ALLOC_FAIL; 233 goto out; 234 } 235 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0) 236 goto out; 237 kex->initial_hostkey = server_host_key; 238 server_host_key = NULL; 239 } 240 /* success */ 241out: 242 explicit_bzero(hash, sizeof(hash)); 243 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 244 explicit_bzero(kex->sntrup761_client_key, 245 sizeof(kex->sntrup761_client_key)); 246 sshbuf_free(server_host_key_blob); 247 free(signature); 248 sshbuf_free(tmp); 249 sshkey_free(server_host_key); 250 sshbuf_free(server_blob); 251 sshbuf_free(shared_secret); 252 sshbuf_free(kex->client_pub); 253 kex->client_pub = NULL; 254 return r; 255} 256 257int 258kex_gen_server(struct ssh *ssh) 259{ 260 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 261 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); 262 return 0; 263} 264 265static int 266input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) 267{ 268 struct kex *kex = ssh->kex; 269 struct sshkey *server_host_private, *server_host_public; 270 struct sshbuf *shared_secret = NULL; 271 struct sshbuf *server_pubkey = NULL; 272 struct sshbuf *client_pubkey = NULL; 273 struct sshbuf *server_host_key_blob = NULL; 274 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; 275 size_t slen, hashlen; 276 int r; 277 278 debug("SSH2_MSG_KEX_ECDH_INIT received"); 279 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error); 280 281 if ((r = kex_load_hostkey(ssh, &server_host_private, 282 &server_host_public)) != 0) 283 goto out; 284 285 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 286 (r = sshpkt_get_end(ssh)) != 0) 287 goto out; 288 289 /* compute shared secret */ 290 switch (kex->kex_type) { 291#ifdef WITH_OPENSSL 292 case KEX_DH_GRP1_SHA1: 293 case KEX_DH_GRP14_SHA1: 294 case KEX_DH_GRP14_SHA256: 295 case KEX_DH_GRP16_SHA512: 296 case KEX_DH_GRP18_SHA512: 297 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 298 &shared_secret); 299 break; 300 case KEX_ECDH_SHA2: 301 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 302 &shared_secret); 303 break; 304#endif 305 case KEX_C25519_SHA256: 306 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 307 &shared_secret); 308 break; 309 case KEX_KEM_SNTRUP761X25519_SHA512: 310 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey, 311 &server_pubkey, &shared_secret); 312 break; 313 default: 314 r = SSH_ERR_INVALID_ARGUMENT; 315 break; 316 } 317 if (r !=0 ) 318 goto out; 319 320 /* calc H */ 321 if ((server_host_key_blob = sshbuf_new()) == NULL) { 322 r = SSH_ERR_ALLOC_FAIL; 323 goto out; 324 } 325 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 326 goto out; 327 hashlen = sizeof(hash); 328 if ((r = kex_gen_hash( 329 kex->hash_alg, 330 kex->client_version, 331 kex->server_version, 332 kex->peer, 333 kex->my, 334 server_host_key_blob, 335 client_pubkey, 336 server_pubkey, 337 shared_secret, 338 hash, &hashlen)) != 0) 339 goto out; 340 341 /* sign H */ 342 if ((r = kex->sign(ssh, server_host_private, server_host_public, 343 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 344 goto out; 345 346 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 347 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 348 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 349 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 350 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 351 (r = sshpkt_send(ssh)) != 0) 352 goto out; 353 354 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 355 (r = kex_send_newkeys(ssh)) != 0) 356 goto out; 357 /* retain copy of hostkey used at initial KEX */ 358 if (kex->initial_hostkey == NULL && 359 (r = sshkey_from_private(server_host_public, 360 &kex->initial_hostkey)) != 0) 361 goto out; 362 /* success */ 363out: 364 explicit_bzero(hash, sizeof(hash)); 365 sshbuf_free(server_host_key_blob); 366 free(signature); 367 sshbuf_free(shared_secret); 368 sshbuf_free(client_pubkey); 369 sshbuf_free(server_pubkey); 370 return r; 371} 372