1 /* $OpenBSD: kexgen.c,v 1.2 2019/01/23 00:30:41 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 case KEX_DH_GRP1_SHA1: 103 case KEX_DH_GRP14_SHA1: 104 case KEX_DH_GRP14_SHA256: 105 case KEX_DH_GRP16_SHA512: 106 case KEX_DH_GRP18_SHA512: 107 r = kex_dh_keypair(kex); 108 break; 109 case KEX_ECDH_SHA2: 110 r = kex_ecdh_keypair(kex); 111 break; 112 case KEX_C25519_SHA256: 113 r = kex_c25519_keypair(kex); 114 break; 115 case KEX_KEM_SNTRUP4591761X25519_SHA512: 116 r = kex_kem_sntrup4591761x25519_keypair(kex); 117 break; 118 default: 119 r = SSH_ERR_INVALID_ARGUMENT; 120 break; 121 } 122 if (r != 0) 123 return r; 124 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 || 125 (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 || 126 (r = sshpkt_send(ssh)) != 0) 127 return r; 128 debug("expecting SSH2_MSG_KEX_ECDH_REPLY"); 129 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply); 130 return 0; 131 } 132 133 static int 134 input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh) 135 { 136 struct kex *kex = ssh->kex; 137 struct sshkey *server_host_key = NULL; 138 struct sshbuf *shared_secret = NULL; 139 struct sshbuf *server_blob = NULL; 140 struct sshbuf *tmp = NULL, *server_host_key_blob = NULL; 141 u_char *signature = NULL; 142 u_char hash[SSH_DIGEST_MAX_LENGTH]; 143 size_t slen, hashlen; 144 int r; 145 146 /* hostkey */ 147 if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0) 148 goto out; 149 /* sshkey_fromb() consumes its buffer, so make a copy */ 150 if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) { 151 r = SSH_ERR_ALLOC_FAIL; 152 goto out; 153 } 154 if ((r = sshkey_fromb(tmp, &server_host_key)) != 0) 155 goto out; 156 if ((r = kex_verify_host_key(ssh, server_host_key)) != 0) 157 goto out; 158 159 /* Q_S, server public key */ 160 /* signed H */ 161 if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 || 162 (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 || 163 (r = sshpkt_get_end(ssh)) != 0) 164 goto out; 165 166 /* compute shared secret */ 167 switch (kex->kex_type) { 168 case KEX_DH_GRP1_SHA1: 169 case KEX_DH_GRP14_SHA1: 170 case KEX_DH_GRP14_SHA256: 171 case KEX_DH_GRP16_SHA512: 172 case KEX_DH_GRP18_SHA512: 173 r = kex_dh_dec(kex, server_blob, &shared_secret); 174 break; 175 case KEX_ECDH_SHA2: 176 r = kex_ecdh_dec(kex, server_blob, &shared_secret); 177 break; 178 case KEX_C25519_SHA256: 179 r = kex_c25519_dec(kex, server_blob, &shared_secret); 180 break; 181 case KEX_KEM_SNTRUP4591761X25519_SHA512: 182 r = kex_kem_sntrup4591761x25519_dec(kex, server_blob, 183 &shared_secret); 184 break; 185 default: 186 r = SSH_ERR_INVALID_ARGUMENT; 187 break; 188 } 189 if (r !=0 ) 190 goto out; 191 192 /* calc and verify H */ 193 hashlen = sizeof(hash); 194 if ((r = kex_gen_hash( 195 kex->hash_alg, 196 kex->client_version, 197 kex->server_version, 198 kex->my, 199 kex->peer, 200 server_host_key_blob, 201 kex->client_pub, 202 server_blob, 203 shared_secret, 204 hash, &hashlen)) != 0) 205 goto out; 206 207 if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen, 208 kex->hostkey_alg, ssh->compat)) != 0) 209 goto out; 210 211 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 212 r = kex_send_newkeys(ssh); 213 out: 214 explicit_bzero(hash, sizeof(hash)); 215 explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key)); 216 explicit_bzero(kex->sntrup4591761_client_key, 217 sizeof(kex->sntrup4591761_client_key)); 218 sshbuf_free(server_host_key_blob); 219 free(signature); 220 sshbuf_free(tmp); 221 sshkey_free(server_host_key); 222 sshbuf_free(server_blob); 223 sshbuf_free(shared_secret); 224 sshbuf_free(kex->client_pub); 225 kex->client_pub = NULL; 226 return r; 227 } 228 229 int 230 kex_gen_server(struct ssh *ssh) 231 { 232 debug("expecting SSH2_MSG_KEX_ECDH_INIT"); 233 ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init); 234 return 0; 235 } 236 237 static int 238 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh) 239 { 240 struct kex *kex = ssh->kex; 241 struct sshkey *server_host_private, *server_host_public; 242 struct sshbuf *shared_secret = NULL; 243 struct sshbuf *server_pubkey = NULL; 244 struct sshbuf *client_pubkey = NULL; 245 struct sshbuf *server_host_key_blob = NULL; 246 u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH]; 247 size_t slen, hashlen; 248 int r; 249 250 if ((r = kex_load_hostkey(ssh, &server_host_private, 251 &server_host_public)) != 0) 252 goto out; 253 254 if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 || 255 (r = sshpkt_get_end(ssh)) != 0) 256 goto out; 257 258 /* compute shared secret */ 259 switch (kex->kex_type) { 260 case KEX_DH_GRP1_SHA1: 261 case KEX_DH_GRP14_SHA1: 262 case KEX_DH_GRP14_SHA256: 263 case KEX_DH_GRP16_SHA512: 264 case KEX_DH_GRP18_SHA512: 265 r = kex_dh_enc(kex, client_pubkey, &server_pubkey, 266 &shared_secret); 267 break; 268 case KEX_ECDH_SHA2: 269 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey, 270 &shared_secret); 271 break; 272 case KEX_C25519_SHA256: 273 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey, 274 &shared_secret); 275 break; 276 case KEX_KEM_SNTRUP4591761X25519_SHA512: 277 r = kex_kem_sntrup4591761x25519_enc(kex, client_pubkey, 278 &server_pubkey, &shared_secret); 279 break; 280 default: 281 r = SSH_ERR_INVALID_ARGUMENT; 282 break; 283 } 284 if (r !=0 ) 285 goto out; 286 287 /* calc H */ 288 if ((server_host_key_blob = sshbuf_new()) == NULL) { 289 r = SSH_ERR_ALLOC_FAIL; 290 goto out; 291 } 292 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 293 goto out; 294 hashlen = sizeof(hash); 295 if ((r = kex_gen_hash( 296 kex->hash_alg, 297 kex->client_version, 298 kex->server_version, 299 kex->peer, 300 kex->my, 301 server_host_key_blob, 302 client_pubkey, 303 server_pubkey, 304 shared_secret, 305 hash, &hashlen)) != 0) 306 goto out; 307 308 /* sign H */ 309 if ((r = kex->sign(ssh, server_host_private, server_host_public, 310 &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0) 311 goto out; 312 313 /* send server hostkey, ECDH pubkey 'Q_S' and signed H */ 314 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 || 315 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 316 (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 || 317 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 318 (r = sshpkt_send(ssh)) != 0) 319 goto out; 320 321 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 322 r = kex_send_newkeys(ssh); 323 out: 324 explicit_bzero(hash, sizeof(hash)); 325 sshbuf_free(server_host_key_blob); 326 free(signature); 327 sshbuf_free(shared_secret); 328 sshbuf_free(client_pubkey); 329 sshbuf_free(server_pubkey); 330 return r; 331 } 332