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 <sys/types.h> 27 28#include <stdio.h> 29#include <string.h> 30#include <signal.h> 31 32#include "sshkey.h" 33#include "kex.h" 34#include "log.h" 35#include "packet.h" 36#include "ssh2.h" 37#include "sshbuf.h" 38#include "digest.h" 39#include "ssherr.h" 40 41static int input_kex_gen_init(int, u_int32_t, struct ssh *); 42static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh); 43 44static int 45kex_gen_hash( 46 int hash_alg, 47 const struct sshbuf *client_version, 48 const struct sshbuf *server_version, 49 const struct sshbuf *client_kexinit, 50 const struct sshbuf *server_kexinit, 51 const struct sshbuf *server_host_key_blob, 52 const struct sshbuf *client_pub, 53 const struct sshbuf *server_pub, 54 const struct sshbuf *shared_secret, 55 u_char *hash, size_t *hashlen) 56{ 57 struct sshbuf *b; 58 int r; 59 60 if (*hashlen < ssh_digest_bytes(hash_alg)) 61 return SSH_ERR_INVALID_ARGUMENT; 62 if ((b = sshbuf_new()) == NULL) 63 return SSH_ERR_ALLOC_FAIL; 64 if ((r = sshbuf_put_stringb(b, client_version)) != 0 || 65 (r = sshbuf_put_stringb(b, server_version)) != 0 || 66 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ 67 (r = sshbuf_put_u32(b, sshbuf_len(client_kexinit) + 1)) != 0 || 68 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 || 69 (r = sshbuf_putb(b, client_kexinit)) != 0 || 70 (r = sshbuf_put_u32(b, sshbuf_len(server_kexinit) + 1)) != 0 || 71 (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 || 72 (r = sshbuf_putb(b, server_kexinit)) != 0 || 73 (r = sshbuf_put_stringb(b, server_host_key_blob)) != 0 || 74 (r = sshbuf_put_stringb(b, client_pub)) != 0 || 75 (r = sshbuf_put_stringb(b, server_pub)) != 0 || 76 (r = sshbuf_putb(b, shared_secret)) != 0) { 77 sshbuf_free(b); 78 return r; 79 } 80#ifdef DEBUG_KEX 81 sshbuf_dump(b, stderr); 82#endif 83 if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) { 84 sshbuf_free(b); 85 return SSH_ERR_LIBCRYPTO_ERROR; 86 } 87 sshbuf_free(b); 88 *hashlen = ssh_digest_bytes(hash_alg); 89#ifdef DEBUG_KEX 90 dump_digest("hash", hash, *hashlen); 91#endif 92 return 0; 93} 94 95int 96kex_gen_client(struct ssh *ssh) 97{ 98 struct kex *kex = ssh->kex; 99 int r; 100 101 switch (kex->kex_type) { 102#ifdef WITH_OPENSSL 103 case KEX_DH_GRP1_SHA1: 104 case KEX_DH_GRP14_SHA1: 105 case KEX_DH_GRP14_SHA256: 106 case KEX_DH_GRP16_SHA512: 107 case KEX_DH_GRP18_SHA512: 108 r = kex_dh_keypair(kex); 109 break; 110 case KEX_ECDH_SHA2: 111 r = kex_ecdh_keypair(kex); 112 break; 113#endif /* WITH_OPENSSL */ 114 case KEX_C25519_SHA256: 115 r = kex_c25519_keypair(kex); 116 break; 117 case KEX_KEM_SNTRUP761X25519_SHA512: 118 r = kex_kem_sntrup761x25519_keypair(kex); 119 break; 120 default: 121 r = SSH_ERR_INVALID_ARGUMENT; 122 break; 123 } 124 if (r != 0) 125 return r; 126 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 || 127 (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 || 128 (r = sshpkt_send(ssh)) != 0) 129 return r; 130 debug("expecting SSH2_MSG_KEX_ECDH_REPLY"); 131 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply); 132 return 0; 133} 134 135static int 136input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh) 137{ 138 struct kex *kex = ssh->kex; 139 struct sshkey *server_host_key = NULL; 140 struct sshbuf *shared_secret = NULL; 141 struct sshbuf *server_blob = NULL; 142 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL; 143 u_char *signature = NULL; 144 u_char hash[SSH_DIGEST_MAX_LENGTH]; 145 size_t slen, hashlen; 146 int r; 147 148 debug("SSH2_MSG_KEX_ECDH_REPLY received"); 149 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &kex_protocol_error); 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 /* WITH_OPENSSL */ 185 case KEX_C25519_SHA256: 186 r = kex_c25519_dec(kex, server_blob, &shared_secret); 187 break; 188 case KEX_KEM_SNTRUP761X25519_SHA512: 189 r = kex_kem_sntrup761x25519_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)) != 0) 220 goto out; 221 222 /* save initial signature and hostkey */ 223 if ((kex->flags & KEX_INITIAL) != 0) { 224 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) { 225 r = SSH_ERR_INTERNAL_ERROR; 226 goto out; 227 } 228 if ((kex->initial_sig = sshbuf_new()) == NULL) { 229 r = SSH_ERR_ALLOC_FAIL; 230 goto out; 231 } 232 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0) 233 goto out; 234 kex->initial_hostkey = server_host_key; 235 server_host_key = NULL; 236 } 237 /* success */ 238out: 239 explicit_bzero(hash, sizeof(hash)); 240 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 241 explicit_bzero(kex->sntrup761_client_key, 242 sizeof(kex->sntrup761_client_key)); 243 sshbuf_free(server_host_key_blob); 244 free(signature); 245 sshbuf_free(tmp); 246 sshkey_free(server_host_key); 247 sshbuf_free(server_blob); 248 sshbuf_free(shared_secret); 249 sshbuf_free(kex->client_pub); 250 kex->client_pub = NULL; 251 return r; 252} 253 254int 255kex_gen_server(struct ssh *ssh) 256{ 257 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 258 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); 259 return 0; 260} 261 262static int 263input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) 264{ 265 struct kex *kex = ssh->kex; 266 struct sshkey *server_host_private, *server_host_public; 267 struct sshbuf *shared_secret = NULL; 268 struct sshbuf *server_pubkey = NULL; 269 struct sshbuf *client_pubkey = NULL; 270 struct sshbuf *server_host_key_blob = NULL; 271 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; 272 size_t slen, hashlen; 273 int r; 274 275 debug("SSH2_MSG_KEX_ECDH_INIT received"); 276 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error); 277 278 if ((r = kex_load_hostkey(ssh, &server_host_private, 279 &server_host_public)) != 0) 280 goto out; 281 282 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 283 (r = sshpkt_get_end(ssh)) != 0) 284 goto out; 285 286 /* compute shared secret */ 287 switch (kex->kex_type) { 288#ifdef WITH_OPENSSL 289 case KEX_DH_GRP1_SHA1: 290 case KEX_DH_GRP14_SHA1: 291 case KEX_DH_GRP14_SHA256: 292 case KEX_DH_GRP16_SHA512: 293 case KEX_DH_GRP18_SHA512: 294 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 295 &shared_secret); 296 break; 297 case KEX_ECDH_SHA2: 298 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 299 &shared_secret); 300 break; 301#endif /* WITH_OPENSSL */ 302 case KEX_C25519_SHA256: 303 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 304 &shared_secret); 305 break; 306 case KEX_KEM_SNTRUP761X25519_SHA512: 307 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey, 308 &server_pubkey, &shared_secret); 309 break; 310 default: 311 r = SSH_ERR_INVALID_ARGUMENT; 312 break; 313 } 314 if (r !=0 ) 315 goto out; 316 317 /* calc H */ 318 if ((server_host_key_blob = sshbuf_new()) == NULL) { 319 r = SSH_ERR_ALLOC_FAIL; 320 goto out; 321 } 322 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 323 goto out; 324 hashlen = sizeof(hash); 325 if ((r = kex_gen_hash( 326 kex->hash_alg, 327 kex->client_version, 328 kex->server_version, 329 kex->peer, 330 kex->my, 331 server_host_key_blob, 332 client_pubkey, 333 server_pubkey, 334 shared_secret, 335 hash, &hashlen)) != 0) 336 goto out; 337 338 /* sign H */ 339 if ((r = kex->sign(ssh, server_host_private, server_host_public, 340 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 341 goto out; 342 343 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 344 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 345 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 346 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 347 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 348 (r = sshpkt_send(ssh)) != 0) 349 goto out; 350 351 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 352 (r = kex_send_newkeys(ssh)) != 0) 353 goto out; 354 /* retain copy of hostkey used at initial KEX */ 355 if (kex->initial_hostkey == NULL && 356 (r = sshkey_from_private(server_host_public, 357 &kex->initial_hostkey)) != 0) 358 goto out; 359 /* success */ 360out: 361 explicit_bzero(hash, sizeof(hash)); 362 sshbuf_free(server_host_key_blob); 363 free(signature); 364 sshbuf_free(shared_secret); 365 sshbuf_free(client_pubkey); 366 sshbuf_free(server_pubkey); 367 return r; 368} 369