1 /* $OpenBSD: kexgen.c,v 1.10 2024/09/09 02:39:57 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 case KEX_KEM_MLKEM768X25519_SHA256: 121 r = kex_kem_mlkem768x25519_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 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 /* WITH_OPENSSL */ 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 case KEX_KEM_MLKEM768X25519_SHA256: 196 r = kex_kem_mlkem768x25519_dec(kex, server_blob, 197 &shared_secret); 198 break; 199 default: 200 r = SSH_ERR_INVALID_ARGUMENT; 201 break; 202 } 203 if (r !=0 ) 204 goto out; 205 206 /* calc and verify H */ 207 hashlen = sizeof(hash); 208 if ((r = kex_gen_hash( 209 kex->hash_alg, 210 kex->client_version, 211 kex->server_version, 212 kex->my, 213 kex->peer, 214 server_host_key_blob, 215 kex->client_pub, 216 server_blob, 217 shared_secret, 218 hash, &hashlen)) != 0) 219 goto out; 220 221 if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen, 222 kex->hostkey_alg, ssh->compat, NULL)) != 0) 223 goto out; 224 225 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 226 (r = kex_send_newkeys(ssh)) != 0) 227 goto out; 228 229 /* save initial signature and hostkey */ 230 if ((kex->flags & KEX_INITIAL) != 0) { 231 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) { 232 r = SSH_ERR_INTERNAL_ERROR; 233 goto out; 234 } 235 if ((kex->initial_sig = sshbuf_new()) == NULL) { 236 r = SSH_ERR_ALLOC_FAIL; 237 goto out; 238 } 239 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0) 240 goto out; 241 kex->initial_hostkey = server_host_key; 242 server_host_key = NULL; 243 } 244 /* success */ 245 out: 246 explicit_bzero(hash, sizeof(hash)); 247 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 248 explicit_bzero(kex->sntrup761_client_key, 249 sizeof(kex->sntrup761_client_key)); 250 explicit_bzero(kex->mlkem768_client_key, 251 sizeof(kex->mlkem768_client_key)); 252 sshbuf_free(server_host_key_blob); 253 free(signature); 254 sshbuf_free(tmp); 255 sshkey_free(server_host_key); 256 sshbuf_free(server_blob); 257 sshbuf_free(shared_secret); 258 sshbuf_free(kex->client_pub); 259 kex->client_pub = NULL; 260 return r; 261 } 262 263 int 264 kex_gen_server(struct ssh *ssh) 265 { 266 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 267 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); 268 return 0; 269 } 270 271 static int 272 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) 273 { 274 struct kex *kex = ssh->kex; 275 struct sshkey *server_host_private, *server_host_public; 276 struct sshbuf *shared_secret = NULL; 277 struct sshbuf *server_pubkey = NULL; 278 struct sshbuf *client_pubkey = NULL; 279 struct sshbuf *server_host_key_blob = NULL; 280 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; 281 size_t slen, hashlen; 282 int r; 283 284 debug("SSH2_MSG_KEX_ECDH_INIT received"); 285 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error); 286 287 if ((r = kex_load_hostkey(ssh, &server_host_private, 288 &server_host_public)) != 0) 289 goto out; 290 291 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 292 (r = sshpkt_get_end(ssh)) != 0) 293 goto out; 294 295 /* compute shared secret */ 296 switch (kex->kex_type) { 297 #ifdef WITH_OPENSSL 298 case KEX_DH_GRP1_SHA1: 299 case KEX_DH_GRP14_SHA1: 300 case KEX_DH_GRP14_SHA256: 301 case KEX_DH_GRP16_SHA512: 302 case KEX_DH_GRP18_SHA512: 303 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 304 &shared_secret); 305 break; 306 case KEX_ECDH_SHA2: 307 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 308 &shared_secret); 309 break; 310 #endif /* WITH_OPENSSL */ 311 case KEX_C25519_SHA256: 312 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 313 &shared_secret); 314 break; 315 case KEX_KEM_SNTRUP761X25519_SHA512: 316 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey, 317 &server_pubkey, &shared_secret); 318 break; 319 case KEX_KEM_MLKEM768X25519_SHA256: 320 r = kex_kem_mlkem768x25519_enc(kex, client_pubkey, 321 &server_pubkey, &shared_secret); 322 break; 323 default: 324 r = SSH_ERR_INVALID_ARGUMENT; 325 break; 326 } 327 if (r !=0 ) 328 goto out; 329 330 /* calc H */ 331 if ((server_host_key_blob = sshbuf_new()) == NULL) { 332 r = SSH_ERR_ALLOC_FAIL; 333 goto out; 334 } 335 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 336 goto out; 337 hashlen = sizeof(hash); 338 if ((r = kex_gen_hash( 339 kex->hash_alg, 340 kex->client_version, 341 kex->server_version, 342 kex->peer, 343 kex->my, 344 server_host_key_blob, 345 client_pubkey, 346 server_pubkey, 347 shared_secret, 348 hash, &hashlen)) != 0) 349 goto out; 350 351 /* sign H */ 352 if ((r = kex->sign(ssh, server_host_private, server_host_public, 353 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 354 goto out; 355 356 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 357 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 358 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 359 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 360 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 361 (r = sshpkt_send(ssh)) != 0) 362 goto out; 363 364 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 365 (r = kex_send_newkeys(ssh)) != 0) 366 goto out; 367 /* retain copy of hostkey used at initial KEX */ 368 if (kex->initial_hostkey == NULL && 369 (r = sshkey_from_private(server_host_public, 370 &kex->initial_hostkey)) != 0) 371 goto out; 372 /* success */ 373 out: 374 explicit_bzero(hash, sizeof(hash)); 375 sshbuf_free(server_host_key_blob); 376 free(signature); 377 sshbuf_free(shared_secret); 378 sshbuf_free(client_pubkey); 379 sshbuf_free(server_pubkey); 380 return r; 381 } 382