/* $OpenBSD: kexgen.c,v 1.7 2021/04/03 06:18:40 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);
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);
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;
}
