1 /* $OpenBSD: kexgen.c,v 1.7 2021/04/03 06:18:40 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 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 } 134 135 static int 136 input_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); 220 out: 221 explicit_bzero(hash, sizeof(hash)); 222 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 223 explicit_bzero(kex->sntrup761_client_key, 224 sizeof(kex->sntrup761_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 debug("SSH2_MSG_KEX_ECDH_INIT received"); 258 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error); 259 260 if ((r = kex_load_hostkey(ssh, &server_host_private, 261 &server_host_public)) != 0) 262 goto out; 263 264 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 265 (r = sshpkt_get_end(ssh)) != 0) 266 goto out; 267 268 /* compute shared secret */ 269 switch (kex->kex_type) { 270 #ifdef WITH_OPENSSL 271 case KEX_DH_GRP1_SHA1: 272 case KEX_DH_GRP14_SHA1: 273 case KEX_DH_GRP14_SHA256: 274 case KEX_DH_GRP16_SHA512: 275 case KEX_DH_GRP18_SHA512: 276 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 277 &shared_secret); 278 break; 279 case KEX_ECDH_SHA2: 280 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 281 &shared_secret); 282 break; 283 #endif /* WITH_OPENSSL */ 284 case KEX_C25519_SHA256: 285 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 286 &shared_secret); 287 break; 288 case KEX_KEM_SNTRUP761X25519_SHA512: 289 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey, 290 &server_pubkey, &shared_secret); 291 break; 292 default: 293 r = SSH_ERR_INVALID_ARGUMENT; 294 break; 295 } 296 if (r !=0 ) 297 goto out; 298 299 /* calc H */ 300 if ((server_host_key_blob = sshbuf_new()) == NULL) { 301 r = SSH_ERR_ALLOC_FAIL; 302 goto out; 303 } 304 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 305 goto out; 306 hashlen = sizeof(hash); 307 if ((r = kex_gen_hash( 308 kex->hash_alg, 309 kex->client_version, 310 kex->server_version, 311 kex->peer, 312 kex->my, 313 server_host_key_blob, 314 client_pubkey, 315 server_pubkey, 316 shared_secret, 317 hash, &hashlen)) != 0) 318 goto out; 319 320 /* sign H */ 321 if ((r = kex->sign(ssh, server_host_private, server_host_public, 322 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 323 goto out; 324 325 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 326 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 327 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 328 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 329 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 330 (r = sshpkt_send(ssh)) != 0) 331 goto out; 332 333 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 334 r = kex_send_newkeys(ssh); 335 out: 336 explicit_bzero(hash, sizeof(hash)); 337 sshbuf_free(server_host_key_blob); 338 free(signature); 339 sshbuf_free(shared_secret); 340 sshbuf_free(client_pubkey); 341 sshbuf_free(server_pubkey); 342 return r; 343 } 344