1 /* $OpenBSD: kexgen.c,v 1.9 2024/09/02 12:13:56 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 41 static int input_kex_gen_init(int, u_int32_t, struct ssh *); 42 static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh); 43 44 static int 45 kex_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 95 int 96 kex_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 #ifdef WITH_MLKEM 121 case KEX_KEM_MLKEM768X25519_SHA256: 122 r = kex_kem_mlkem768x25519_keypair(kex); 123 break; 124 #endif 125 default: 126 r = SSH_ERR_INVALID_ARGUMENT; 127 break; 128 } 129 if (r != 0) 130 return r; 131 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 || 132 (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 || 133 (r = sshpkt_send(ssh)) != 0) 134 return r; 135 debug("expecting SSH2_MSG_KEX_ECDH_REPLY"); 136 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply); 137 return 0; 138 } 139 140 static int 141 input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh) 142 { 143 struct kex *kex = ssh->kex; 144 struct sshkey *server_host_key = NULL; 145 struct sshbuf *shared_secret = NULL; 146 struct sshbuf *server_blob = NULL; 147 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL; 148 u_char *signature = NULL; 149 u_char hash[SSH_DIGEST_MAX_LENGTH]; 150 size_t slen, hashlen; 151 int r; 152 153 debug("SSH2_MSG_KEX_ECDH_REPLY received"); 154 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &kex_protocol_error); 155 156 /* hostkey */ 157 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) 158 goto out; 159 /* sshkey_fromb() consumes its buffer, so make a copy */ 160 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { 161 r = SSH_ERR_ALLOC_FAIL; 162 goto out; 163 } 164 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0) 165 goto out; 166 if ((r = kex_verify_host_key(ssh, server_host_key)) != 0) 167 goto out; 168 169 /* Q_S, server public key */ 170 /* signed H */ 171 if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 || 172 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 173 (r = sshpkt_get_end(ssh)) != 0) 174 goto out; 175 176 /* compute shared secret */ 177 switch (kex->kex_type) { 178 #ifdef WITH_OPENSSL 179 case KEX_DH_GRP1_SHA1: 180 case KEX_DH_GRP14_SHA1: 181 case KEX_DH_GRP14_SHA256: 182 case KEX_DH_GRP16_SHA512: 183 case KEX_DH_GRP18_SHA512: 184 r = kex_dh_dec(kex, server_blob, &shared_secret); 185 break; 186 case KEX_ECDH_SHA2: 187 r = kex_ecdh_dec(kex, server_blob, &shared_secret); 188 break; 189 #endif /* WITH_OPENSSL */ 190 case KEX_C25519_SHA256: 191 r = kex_c25519_dec(kex, server_blob, &shared_secret); 192 break; 193 case KEX_KEM_SNTRUP761X25519_SHA512: 194 r = kex_kem_sntrup761x25519_dec(kex, server_blob, 195 &shared_secret); 196 break; 197 #ifdef WITH_MLKEM 198 case KEX_KEM_MLKEM768X25519_SHA256: 199 r = kex_kem_mlkem768x25519_dec(kex, server_blob, 200 &shared_secret); 201 break; 202 #endif 203 default: 204 r = SSH_ERR_INVALID_ARGUMENT; 205 break; 206 } 207 if (r !=0 ) 208 goto out; 209 210 /* calc and verify H */ 211 hashlen = sizeof(hash); 212 if ((r = kex_gen_hash( 213 kex->hash_alg, 214 kex->client_version, 215 kex->server_version, 216 kex->my, 217 kex->peer, 218 server_host_key_blob, 219 kex->client_pub, 220 server_blob, 221 shared_secret, 222 hash, &hashlen)) != 0) 223 goto out; 224 225 if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen, 226 kex->hostkey_alg, ssh->compat, NULL)) != 0) 227 goto out; 228 229 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 230 (r = kex_send_newkeys(ssh)) != 0) 231 goto out; 232 233 /* save initial signature and hostkey */ 234 if ((kex->flags & KEX_INITIAL) != 0) { 235 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) { 236 r = SSH_ERR_INTERNAL_ERROR; 237 goto out; 238 } 239 if ((kex->initial_sig = sshbuf_new()) == NULL) { 240 r = SSH_ERR_ALLOC_FAIL; 241 goto out; 242 } 243 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0) 244 goto out; 245 kex->initial_hostkey = server_host_key; 246 server_host_key = NULL; 247 } 248 /* success */ 249 out: 250 explicit_bzero(hash, sizeof(hash)); 251 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 252 explicit_bzero(kex->sntrup761_client_key, 253 sizeof(kex->sntrup761_client_key)); 254 explicit_bzero(kex->mlkem768_client_key, 255 sizeof(kex->mlkem768_client_key)); 256 sshbuf_free(server_host_key_blob); 257 free(signature); 258 sshbuf_free(tmp); 259 sshkey_free(server_host_key); 260 sshbuf_free(server_blob); 261 sshbuf_free(shared_secret); 262 sshbuf_free(kex->client_pub); 263 kex->client_pub = NULL; 264 return r; 265 } 266 267 int 268 kex_gen_server(struct ssh *ssh) 269 { 270 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 271 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); 272 return 0; 273 } 274 275 static int 276 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) 277 { 278 struct kex *kex = ssh->kex; 279 struct sshkey *server_host_private, *server_host_public; 280 struct sshbuf *shared_secret = NULL; 281 struct sshbuf *server_pubkey = NULL; 282 struct sshbuf *client_pubkey = NULL; 283 struct sshbuf *server_host_key_blob = NULL; 284 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; 285 size_t slen, hashlen; 286 int r; 287 288 debug("SSH2_MSG_KEX_ECDH_INIT received"); 289 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error); 290 291 if ((r = kex_load_hostkey(ssh, &server_host_private, 292 &server_host_public)) != 0) 293 goto out; 294 295 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 296 (r = sshpkt_get_end(ssh)) != 0) 297 goto out; 298 299 /* compute shared secret */ 300 switch (kex->kex_type) { 301 #ifdef WITH_OPENSSL 302 case KEX_DH_GRP1_SHA1: 303 case KEX_DH_GRP14_SHA1: 304 case KEX_DH_GRP14_SHA256: 305 case KEX_DH_GRP16_SHA512: 306 case KEX_DH_GRP18_SHA512: 307 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 308 &shared_secret); 309 break; 310 case KEX_ECDH_SHA2: 311 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 312 &shared_secret); 313 break; 314 #endif /* WITH_OPENSSL */ 315 case KEX_C25519_SHA256: 316 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 317 &shared_secret); 318 break; 319 case KEX_KEM_SNTRUP761X25519_SHA512: 320 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey, 321 &server_pubkey, &shared_secret); 322 break; 323 #ifdef WITH_MLKEM 324 case KEX_KEM_MLKEM768X25519_SHA256: 325 r = kex_kem_mlkem768x25519_enc(kex, client_pubkey, 326 &server_pubkey, &shared_secret); 327 break; 328 #endif 329 default: 330 r = SSH_ERR_INVALID_ARGUMENT; 331 break; 332 } 333 if (r !=0 ) 334 goto out; 335 336 /* calc H */ 337 if ((server_host_key_blob = sshbuf_new()) == NULL) { 338 r = SSH_ERR_ALLOC_FAIL; 339 goto out; 340 } 341 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 342 goto out; 343 hashlen = sizeof(hash); 344 if ((r = kex_gen_hash( 345 kex->hash_alg, 346 kex->client_version, 347 kex->server_version, 348 kex->peer, 349 kex->my, 350 server_host_key_blob, 351 client_pubkey, 352 server_pubkey, 353 shared_secret, 354 hash, &hashlen)) != 0) 355 goto out; 356 357 /* sign H */ 358 if ((r = kex->sign(ssh, server_host_private, server_host_public, 359 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 360 goto out; 361 362 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 363 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 364 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 365 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 366 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 367 (r = sshpkt_send(ssh)) != 0) 368 goto out; 369 370 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 371 (r = kex_send_newkeys(ssh)) != 0) 372 goto out; 373 /* retain copy of hostkey used at initial KEX */ 374 if (kex->initial_hostkey == NULL && 375 (r = sshkey_from_private(server_host_public, 376 &kex->initial_hostkey)) != 0) 377 goto out; 378 /* success */ 379 out: 380 explicit_bzero(hash, sizeof(hash)); 381 sshbuf_free(server_host_key_blob); 382 free(signature); 383 sshbuf_free(shared_secret); 384 sshbuf_free(client_pubkey); 385 sshbuf_free(server_pubkey); 386 return r; 387 } 388