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 "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 44 static int input_kex_gen_init(int, u_int32_t, struct ssh *); 45 static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh); 46 47 static int 48 kex_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 98 int 99 kex_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 } 137 138 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 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); 223 out: 224 explicit_bzero(hash, sizeof(hash)); 225 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 226 explicit_bzero(kex->sntrup761_client_key, 227 sizeof(kex->sntrup761_client_key)); 228 sshbuf_free(server_host_key_blob); 229 free(signature); 230 sshbuf_free(tmp); 231 sshkey_free(server_host_key); 232 sshbuf_free(server_blob); 233 sshbuf_free(shared_secret); 234 sshbuf_free(kex->client_pub); 235 kex->client_pub = NULL; 236 return r; 237 } 238 239 int 240 kex_gen_server(struct ssh *ssh) 241 { 242 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 243 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); 244 return 0; 245 } 246 247 static int 248 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) 249 { 250 struct kex *kex = ssh->kex; 251 struct sshkey *server_host_private, *server_host_public; 252 struct sshbuf *shared_secret = NULL; 253 struct sshbuf *server_pubkey = NULL; 254 struct sshbuf *client_pubkey = NULL; 255 struct sshbuf *server_host_key_blob = NULL; 256 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; 257 size_t slen, hashlen; 258 int r; 259 260 debug("SSH2_MSG_KEX_ECDH_INIT received"); 261 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error); 262 263 if ((r = kex_load_hostkey(ssh, &server_host_private, 264 &server_host_public)) != 0) 265 goto out; 266 267 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 268 (r = sshpkt_get_end(ssh)) != 0) 269 goto out; 270 271 /* compute shared secret */ 272 switch (kex->kex_type) { 273 #ifdef WITH_OPENSSL 274 case KEX_DH_GRP1_SHA1: 275 case KEX_DH_GRP14_SHA1: 276 case KEX_DH_GRP14_SHA256: 277 case KEX_DH_GRP16_SHA512: 278 case KEX_DH_GRP18_SHA512: 279 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 280 &shared_secret); 281 break; 282 case KEX_ECDH_SHA2: 283 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 284 &shared_secret); 285 break; 286 #endif 287 case KEX_C25519_SHA256: 288 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 289 &shared_secret); 290 break; 291 case KEX_KEM_SNTRUP761X25519_SHA512: 292 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey, 293 &server_pubkey, &shared_secret); 294 break; 295 default: 296 r = SSH_ERR_INVALID_ARGUMENT; 297 break; 298 } 299 if (r !=0 ) 300 goto out; 301 302 /* calc H */ 303 if ((server_host_key_blob = sshbuf_new()) == NULL) { 304 r = SSH_ERR_ALLOC_FAIL; 305 goto out; 306 } 307 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 308 goto out; 309 hashlen = sizeof(hash); 310 if ((r = kex_gen_hash( 311 kex->hash_alg, 312 kex->client_version, 313 kex->server_version, 314 kex->peer, 315 kex->my, 316 server_host_key_blob, 317 client_pubkey, 318 server_pubkey, 319 shared_secret, 320 hash, &hashlen)) != 0) 321 goto out; 322 323 /* sign H */ 324 if ((r = kex->sign(ssh, server_host_private, server_host_public, 325 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 326 goto out; 327 328 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 329 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 330 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 331 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 332 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 333 (r = sshpkt_send(ssh)) != 0) 334 goto out; 335 336 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 337 r = kex_send_newkeys(ssh); 338 out: 339 explicit_bzero(hash, sizeof(hash)); 340 sshbuf_free(server_host_key_blob); 341 free(signature); 342 sshbuf_free(shared_secret); 343 sshbuf_free(client_pubkey); 344 sshbuf_free(server_pubkey); 345 return r; 346 } 347