|
- /* $OpenBSD: kexgen.c,v 1.8 2021/12/19 22:08:06 djm Exp $ */
- /*
- * Copyright (c) 2019 Markus Friedl. All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
- * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
- * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
- * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
- * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
- * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
- #include "includes.h"
-
- #include <sys/types.h>
-
- #include <stdarg.h>
- #include <stdio.h>
- #include <string.h>
- #include <signal.h>
-
- #include "sshkey.h"
- #include "kex.h"
- #include "log.h"
- #include "packet.h"
- #include "ssh2.h"
- #include "sshbuf.h"
- #include "digest.h"
- #include "ssherr.h"
-
- static int input_kex_gen_init(int, u_int32_t, struct ssh *);
- static int input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh);
-
- static int
- kex_gen_hash(
- int hash_alg,
- const struct sshbuf *client_version,
- const struct sshbuf *server_version,
- const struct sshbuf *client_kexinit,
- const struct sshbuf *server_kexinit,
- const struct sshbuf *server_host_key_blob,
- const struct sshbuf *client_pub,
- const struct sshbuf *server_pub,
- const struct sshbuf *shared_secret,
- u_char *hash, size_t *hashlen)
- {
- struct sshbuf *b;
- int r;
-
- if (*hashlen < ssh_digest_bytes(hash_alg))
- return SSH_ERR_INVALID_ARGUMENT;
- if ((b = sshbuf_new()) == NULL)
- return SSH_ERR_ALLOC_FAIL;
- if ((r = sshbuf_put_stringb(b, client_version)) != 0 ||
- (r = sshbuf_put_stringb(b, server_version)) != 0 ||
- /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
- (r = sshbuf_put_u32(b, sshbuf_len(client_kexinit) + 1)) != 0 ||
- (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
- (r = sshbuf_putb(b, client_kexinit)) != 0 ||
- (r = sshbuf_put_u32(b, sshbuf_len(server_kexinit) + 1)) != 0 ||
- (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) != 0 ||
- (r = sshbuf_putb(b, server_kexinit)) != 0 ||
- (r = sshbuf_put_stringb(b, server_host_key_blob)) != 0 ||
- (r = sshbuf_put_stringb(b, client_pub)) != 0 ||
- (r = sshbuf_put_stringb(b, server_pub)) != 0 ||
- (r = sshbuf_putb(b, shared_secret)) != 0) {
- sshbuf_free(b);
- return r;
- }
- #ifdef DEBUG_KEX
- sshbuf_dump(b, stderr);
- #endif
- if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) {
- sshbuf_free(b);
- return SSH_ERR_LIBCRYPTO_ERROR;
- }
- sshbuf_free(b);
- *hashlen = ssh_digest_bytes(hash_alg);
- #ifdef DEBUG_KEX
- dump_digest("hash", hash, *hashlen);
- #endif
- return 0;
- }
-
- int
- kex_gen_client(struct ssh *ssh)
- {
- struct kex *kex = ssh->kex;
- int r;
-
- switch (kex->kex_type) {
- #ifdef WITH_OPENSSL
- case KEX_DH_GRP1_SHA1:
- case KEX_DH_GRP14_SHA1:
- case KEX_DH_GRP14_SHA256:
- case KEX_DH_GRP16_SHA512:
- case KEX_DH_GRP18_SHA512:
- r = kex_dh_keypair(kex);
- break;
- case KEX_ECDH_SHA2:
- r = kex_ecdh_keypair(kex);
- break;
- #endif
- case KEX_C25519_SHA256:
- r = kex_c25519_keypair(kex);
- break;
- case KEX_KEM_SNTRUP761X25519_SHA512:
- r = kex_kem_sntrup761x25519_keypair(kex);
- break;
- default:
- r = SSH_ERR_INVALID_ARGUMENT;
- break;
- }
- if (r != 0)
- return r;
- if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_INIT)) != 0 ||
- (r = sshpkt_put_stringb(ssh, kex->client_pub)) != 0 ||
- (r = sshpkt_send(ssh)) != 0)
- return r;
- debug("expecting SSH2_MSG_KEX_ECDH_REPLY");
- ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &input_kex_gen_reply);
- return 0;
- }
-
- static int
- input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh)
- {
- struct kex *kex = ssh->kex;
- struct sshkey *server_host_key = NULL;
- struct sshbuf *shared_secret = NULL;
- struct sshbuf *server_blob = NULL;
- struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
- u_char *signature = NULL;
- u_char hash[SSH_DIGEST_MAX_LENGTH];
- size_t slen, hashlen;
- int r;
-
- debug("SSH2_MSG_KEX_ECDH_REPLY received");
- ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_REPLY, &kex_protocol_error);
-
- /* hostkey */
- if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
- goto out;
- /* sshkey_fromb() consumes its buffer, so make a copy */
- if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
- r = SSH_ERR_ALLOC_FAIL;
- goto out;
- }
- if ((r = sshkey_fromb(tmp, &server_host_key)) != 0)
- goto out;
- if ((r = kex_verify_host_key(ssh, server_host_key)) != 0)
- goto out;
-
- /* Q_S, server public key */
- /* signed H */
- if ((r = sshpkt_getb_froms(ssh, &server_blob)) != 0 ||
- (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
- (r = sshpkt_get_end(ssh)) != 0)
- goto out;
-
- /* compute shared secret */
- switch (kex->kex_type) {
- #ifdef WITH_OPENSSL
- case KEX_DH_GRP1_SHA1:
- case KEX_DH_GRP14_SHA1:
- case KEX_DH_GRP14_SHA256:
- case KEX_DH_GRP16_SHA512:
- case KEX_DH_GRP18_SHA512:
- r = kex_dh_dec(kex, server_blob, &shared_secret);
- break;
- case KEX_ECDH_SHA2:
- r = kex_ecdh_dec(kex, server_blob, &shared_secret);
- break;
- #endif
- case KEX_C25519_SHA256:
- r = kex_c25519_dec(kex, server_blob, &shared_secret);
- break;
- case KEX_KEM_SNTRUP761X25519_SHA512:
- r = kex_kem_sntrup761x25519_dec(kex, server_blob,
- &shared_secret);
- break;
- default:
- r = SSH_ERR_INVALID_ARGUMENT;
- break;
- }
- if (r !=0 )
- goto out;
-
- /* calc and verify H */
- hashlen = sizeof(hash);
- if ((r = kex_gen_hash(
- kex->hash_alg,
- kex->client_version,
- kex->server_version,
- kex->my,
- kex->peer,
- server_host_key_blob,
- kex->client_pub,
- server_blob,
- shared_secret,
- hash, &hashlen)) != 0)
- goto out;
-
- if ((r = sshkey_verify(server_host_key, signature, slen, hash, hashlen,
- kex->hostkey_alg, ssh->compat, NULL)) != 0)
- goto out;
-
- if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
- (r = kex_send_newkeys(ssh)) != 0)
- goto out;
-
- /* save initial signature and hostkey */
- if ((kex->flags & KEX_INITIAL) != 0) {
- if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
- r = SSH_ERR_INTERNAL_ERROR;
- goto out;
- }
- if ((kex->initial_sig = sshbuf_new()) == NULL) {
- r = SSH_ERR_ALLOC_FAIL;
- goto out;
- }
- if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
- goto out;
- kex->initial_hostkey = server_host_key;
- server_host_key = NULL;
- }
- /* success */
- out:
- explicit_bzero(hash, sizeof(hash));
- explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key));
- explicit_bzero(kex->sntrup761_client_key,
- sizeof(kex->sntrup761_client_key));
- sshbuf_free(server_host_key_blob);
- free(signature);
- sshbuf_free(tmp);
- sshkey_free(server_host_key);
- sshbuf_free(server_blob);
- sshbuf_free(shared_secret);
- sshbuf_free(kex->client_pub);
- kex->client_pub = NULL;
- return r;
- }
-
- int
- kex_gen_server(struct ssh *ssh)
- {
- debug("expecting SSH2_MSG_KEX_ECDH_INIT");
- ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &input_kex_gen_init);
- return 0;
- }
-
- static int
- input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh)
- {
- struct kex *kex = ssh->kex;
- struct sshkey *server_host_private, *server_host_public;
- struct sshbuf *shared_secret = NULL;
- struct sshbuf *server_pubkey = NULL;
- struct sshbuf *client_pubkey = NULL;
- struct sshbuf *server_host_key_blob = NULL;
- u_char *signature = NULL, hash[SSH_DIGEST_MAX_LENGTH];
- size_t slen, hashlen;
- int r;
-
- debug("SSH2_MSG_KEX_ECDH_INIT received");
- ssh_dispatch_set(ssh, SSH2_MSG_KEX_ECDH_INIT, &kex_protocol_error);
-
- if ((r = kex_load_hostkey(ssh, &server_host_private,
- &server_host_public)) != 0)
- goto out;
-
- if ((r = sshpkt_getb_froms(ssh, &client_pubkey)) != 0 ||
- (r = sshpkt_get_end(ssh)) != 0)
- goto out;
-
- /* compute shared secret */
- switch (kex->kex_type) {
- #ifdef WITH_OPENSSL
- case KEX_DH_GRP1_SHA1:
- case KEX_DH_GRP14_SHA1:
- case KEX_DH_GRP14_SHA256:
- case KEX_DH_GRP16_SHA512:
- case KEX_DH_GRP18_SHA512:
- r = kex_dh_enc(kex, client_pubkey, &server_pubkey,
- &shared_secret);
- break;
- case KEX_ECDH_SHA2:
- r = kex_ecdh_enc(kex, client_pubkey, &server_pubkey,
- &shared_secret);
- break;
- #endif
- case KEX_C25519_SHA256:
- r = kex_c25519_enc(kex, client_pubkey, &server_pubkey,
- &shared_secret);
- break;
- case KEX_KEM_SNTRUP761X25519_SHA512:
- r = kex_kem_sntrup761x25519_enc(kex, client_pubkey,
- &server_pubkey, &shared_secret);
- break;
- default:
- r = SSH_ERR_INVALID_ARGUMENT;
- break;
- }
- if (r !=0 )
- goto out;
-
- /* calc H */
- if ((server_host_key_blob = sshbuf_new()) == NULL) {
- r = SSH_ERR_ALLOC_FAIL;
- goto out;
- }
- if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
- goto out;
- hashlen = sizeof(hash);
- if ((r = kex_gen_hash(
- kex->hash_alg,
- kex->client_version,
- kex->server_version,
- kex->peer,
- kex->my,
- server_host_key_blob,
- client_pubkey,
- server_pubkey,
- shared_secret,
- hash, &hashlen)) != 0)
- goto out;
-
- /* sign H */
- if ((r = kex->sign(ssh, server_host_private, server_host_public,
- &signature, &slen, hash, hashlen, kex->hostkey_alg)) != 0)
- goto out;
-
- /* send server hostkey, ECDH pubkey 'Q_S' and signed H */
- if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_ECDH_REPLY)) != 0 ||
- (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
- (r = sshpkt_put_stringb(ssh, server_pubkey)) != 0 ||
- (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
- (r = sshpkt_send(ssh)) != 0)
- goto out;
-
- if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
- (r = kex_send_newkeys(ssh)) != 0)
- goto out;
- /* retain copy of hostkey used at initial KEX */
- if (kex->initial_hostkey == NULL &&
- (r = sshkey_from_private(server_host_public,
- &kex->initial_hostkey)) != 0)
- goto out;
- /* success */
- out:
- explicit_bzero(hash, sizeof(hash));
- sshbuf_free(server_host_key_blob);
- free(signature);
- sshbuf_free(shared_secret);
- sshbuf_free(client_pubkey);
- sshbuf_free(server_pubkey);
- return r;
- }
|