1 /* $OpenBSD: kexgen.c,v 1.5 2020/12/29 00:59:15 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 /* hostkey */ 149 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) 150 goto out; 151 /* sshkey_fromb() consumes its buffer, so make a copy */ 152 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { 153 r = SSH_ERR_ALLOC_FAIL; 154 goto out; 155 } 156 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0) 157 goto out; 158 if ((r = kex_verify_host_key(ssh, server_host_key)) != 0) 159 goto out; 160 161 /* Q_S, server public key */ 162 /* signed H */ 163 if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 || 164 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 165 (r = sshpkt_get_end(ssh)) != 0) 166 goto out; 167 168 /* compute shared secret */ 169 switch (kex->kex_type) { 170 #ifdef WITH_OPENSSL 171 case KEX_DH_GRP1_SHA1: 172 case KEX_DH_GRP14_SHA1: 173 case KEX_DH_GRP14_SHA256: 174 case KEX_DH_GRP16_SHA512: 175 case KEX_DH_GRP18_SHA512: 176 r = kex_dh_dec(kex, server_blob, &shared_secret); 177 break; 178 case KEX_ECDH_SHA2: 179 r = kex_ecdh_dec(kex, server_blob, &shared_secret); 180 break; 181 #endif /* WITH_OPENSSL */ 182 case KEX_C25519_SHA256: 183 r = kex_c25519_dec(kex, server_blob, &shared_secret); 184 break; 185 case KEX_KEM_SNTRUP761X25519_SHA512: 186 r = kex_kem_sntrup761x25519_dec(kex, server_blob, 187 &shared_secret); 188 break; 189 default: 190 r = SSH_ERR_INVALID_ARGUMENT; 191 break; 192 } 193 if (r !=0 ) 194 goto out; 195 196 /* calc and verify H */ 197 hashlen = sizeof(hash); 198 if ((r = kex_gen_hash( 199 kex->hash_alg, 200 kex->client_version, 201 kex->server_version, 202 kex->my, 203 kex->peer, 204 server_host_key_blob, 205 kex->client_pub, 206 server_blob, 207 shared_secret, 208 hash, &hashlen)) != 0) 209 goto out; 210 211 if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen, 212 kex->hostkey_alg, ssh->compat, NULL)) != 0) 213 goto out; 214 215 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 216 r = kex_send_newkeys(ssh); 217 out: 218 explicit_bzero(hash, sizeof(hash)); 219 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 220 explicit_bzero(kex->sntrup761_client_key, 221 sizeof(kex->sntrup761_client_key)); 222 sshbuf_free(server_host_key_blob); 223 free(signature); 224 sshbuf_free(tmp); 225 sshkey_free(server_host_key); 226 sshbuf_free(server_blob); 227 sshbuf_free(shared_secret); 228 sshbuf_free(kex->client_pub); 229 kex->client_pub = NULL; 230 return r; 231 } 232 233 int 234 kex_gen_server(struct ssh *ssh) 235 { 236 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 237 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); 238 return 0; 239 } 240 241 static int 242 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) 243 { 244 struct kex *kex = ssh->kex; 245 struct sshkey *server_host_private, *server_host_public; 246 struct sshbuf *shared_secret = NULL; 247 struct sshbuf *server_pubkey = NULL; 248 struct sshbuf *client_pubkey = NULL; 249 struct sshbuf *server_host_key_blob = NULL; 250 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; 251 size_t slen, hashlen; 252 int r; 253 254 if ((r = kex_load_hostkey(ssh, &server_host_private, 255 &server_host_public)) != 0) 256 goto out; 257 258 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 259 (r = sshpkt_get_end(ssh)) != 0) 260 goto out; 261 262 /* compute shared secret */ 263 switch (kex->kex_type) { 264 #ifdef WITH_OPENSSL 265 case KEX_DH_GRP1_SHA1: 266 case KEX_DH_GRP14_SHA1: 267 case KEX_DH_GRP14_SHA256: 268 case KEX_DH_GRP16_SHA512: 269 case KEX_DH_GRP18_SHA512: 270 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 271 &shared_secret); 272 break; 273 case KEX_ECDH_SHA2: 274 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 275 &shared_secret); 276 break; 277 #endif /* WITH_OPENSSL */ 278 case KEX_C25519_SHA256: 279 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 280 &shared_secret); 281 break; 282 case KEX_KEM_SNTRUP761X25519_SHA512: 283 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey, 284 &server_pubkey, &shared_secret); 285 break; 286 default: 287 r = SSH_ERR_INVALID_ARGUMENT; 288 break; 289 } 290 if (r !=0 ) 291 goto out; 292 293 /* calc H */ 294 if ((server_host_key_blob = sshbuf_new()) == NULL) { 295 r = SSH_ERR_ALLOC_FAIL; 296 goto out; 297 } 298 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 299 goto out; 300 hashlen = sizeof(hash); 301 if ((r = kex_gen_hash( 302 kex->hash_alg, 303 kex->client_version, 304 kex->server_version, 305 kex->peer, 306 kex->my, 307 server_host_key_blob, 308 client_pubkey, 309 server_pubkey, 310 shared_secret, 311 hash, &hashlen)) != 0) 312 goto out; 313 314 /* sign H */ 315 if ((r = kex->sign(ssh, server_host_private, server_host_public, 316 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 317 goto out; 318 319 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 320 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 321 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 322 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 323 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 324 (r = sshpkt_send(ssh)) != 0) 325 goto out; 326 327 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 328 r = kex_send_newkeys(ssh); 329 out: 330 explicit_bzero(hash, sizeof(hash)); 331 sshbuf_free(server_host_key_blob); 332 free(signature); 333 sshbuf_free(shared_secret); 334 sshbuf_free(client_pubkey); 335 sshbuf_free(server_pubkey); 336 return r; 337 } 338