crypto/openssh/kexgen.c

   1 /* $OpenBSD: kexgen.c,v 1.8 2021/12/19 22:08:06 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)) != 0)
 223                 goto out;
 224
 225         /* save initial signature and hostkey */
 226         if ((kex->flags & KEX_INITIAL) != 0) {
 227                 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
 228                         r = SSH_ERR_INTERNAL_ERROR;
 229                         goto out;
 230                 }
 231                 if ((kex->initial_sig = sshbuf_new()) == NULL) {
 232                         r = SSH_ERR_ALLOC_FAIL;
 233                         goto out;
 234                 }
 235                 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
 236                         goto out;
 237                 kex->initial_hostkey = server_host_key;
 238                 server_host_key = NULL;
 239         }
 240         /* success */
 241 out:
 242         explicit_bzero(hash, sizeof(hash));
 243         explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key));
 244         explicit_bzero(kex->sntrup761_client_key,
 245             sizeof(kex->sntrup761_client_key));
 246         sshbuf_free(server_host_key_blob);
 247         free(signature);
 248         sshbuf_free(tmp);
 249         sshkey_free(server_host_key);
 250         sshbuf_free(server_blob);
 251         sshbuf_free(shared_secret);
 252         sshbuf_free(kex->client_pub);
 253         kex->client_pub = NULL;
 254         return r;
 255 }
 256
 257 int
 258 kex_gen_server(struct ssh *ssh)
 259 {
 260         debug("expecting SSH2_MSG_KEX_ECDH_INIT");
 261         ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init);
 262         return 0;
 263 }
 264
 265 static int
 266 input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh)
 267 {
 268         struct kex *kex = ssh->kex;
 269         struct sshkey *server_host_private, *server_host_public;
 270         struct sshbuf *shared_secret = NULL;
 271         struct sshbuf *server_pubkey = NULL;
 272         struct sshbuf *client_pubkey = NULL;
 273         struct sshbuf *server_host_key_blob = NULL;
 274         u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH];
 275         size_t slen, hashlen;
 276         int r;
 277
 278         debug("SSH2_MSG_KEX_ECDH_INIT received");
 279         ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error);
 280
 281         if ((r = kex_load_hostkey(ssh, &server_host_private,
 282             &server_host_public)) != 0)
 283                 goto out;
 284
 285         if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 ||
 286             (r = sshpkt_get_end(ssh)) != 0)
 287                 goto out;
 288
 289         /* compute shared secret */
 290         switch (kex->kex_type) {
 291 #ifdef WITH_OPENSSL
 292         case KEX_DH_GRP1_SHA1:
 293         case KEX_DH_GRP14_SHA1:
 294         case KEX_DH_GRP14_SHA256:
 295         case KEX_DH_GRP16_SHA512:
 296         case KEX_DH_GRP18_SHA512:
 297                 r = kex_dh_enc(kex, client_pubkey, &server_pubkey,
 298                     &shared_secret);
 299                 break;
 300         case KEX_ECDH_SHA2:
 301                 r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey,
 302                     &shared_secret);
 303                 break;
 304 #endif
 305         case KEX_C25519_SHA256:
 306                 r = kex_c25519_enc(kex, client_pubkey, &server_pubkey,
 307                     &shared_secret);
 308                 break;
 309         case KEX_KEM_SNTRUP761X25519_SHA512:
 310                 r = kex_kem_sntrup761x25519_enc(kex, client_pubkey,
 311                     &server_pubkey, &shared_secret);
 312                 break;
 313         default:
 314                 r = SSH_ERR_INVALID_ARGUMENT;
 315                 break;
 316         }
 317         if (r !=0 )
 318                 goto out;
 319
 320         /* calc H */
 321         if ((server_host_key_blob = sshbuf_new()) == NULL) {
 322                 r = SSH_ERR_ALLOC_FAIL;
 323                 goto out;
 324         }
 325         if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
 326                 goto out;
 327         hashlen = sizeof(hash);
 328         if ((r = kex_gen_hash(
 329             kex->hash_alg,
 330             kex->client_version,
 331             kex->server_version,
 332             kex->peer,
 333             kex->my,
 334             server_host_key_blob,
 335             client_pubkey,
 336             server_pubkey,
 337             shared_secret,
 338             hash, &hashlen)) != 0)
 339                 goto out;
 340
 341         /* sign H */
 342         if ((r = kex->sign(ssh, server_host_private, server_host_public,
 343             &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0)
 344                 goto out;
 345
 346         /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
 347         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
 348             (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
 349             (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 ||
 350             (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
 351             (r = sshpkt_send(ssh)) != 0)
 352                 goto out;
 353
 354         if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
 355             (r = kex_send_newkeys(ssh)) != 0)
 356                 goto out;
 357         /* retain copy of hostkey used at initial KEX */
 358         if (kex->initial_hostkey == NULL &&
 359             (r = sshkey_from_private(server_host_public,
 360             &kex->initial_hostkey)) != 0)
 361                 goto out;
 362         /* success */
 363 out:
 364         explicit_bzero(hash, sizeof(hash));
 365         sshbuf_free(server_host_key_blob);
 366         free(signature);
 367         sshbuf_free(shared_secret);
 368         sshbuf_free(client_pubkey);
 369         sshbuf_free(server_pubkey);
 370         return r;
 371 }