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/* $OpenBSD: kexgexs.c,v 1.47 2024/05/17 00:30:23 djm Exp $ */
/*
* Copyright (c) 2000 Niels Provos. All rights reserved.
* Copyright (c) 2001 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 <stdio.h>
#include <string.h>
#include <signal.h>
#include <openssl/dh.h>
#include "sshkey.h"
#include "cipher.h"
#include "digest.h"
#include "kex.h"
#include "log.h"
#include "packet.h"
#include "dh.h"
#include "ssh2.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"
#include "dispatch.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "misc.h"
static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *);
static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *);
int
kexgex_server(struct ssh *ssh)
{
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST,
&input_kex_dh_gex_request);
debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST");
return 0;
}
static int
input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh)
{
struct kex *kex = ssh->kex;
int r;
u_int min = 0, max = 0, nbits = 0;
const BIGNUM *dh_p, *dh_g;
debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error);
if ((r = sshpkt_get_u32(ssh, &min)) != 0 ||
(r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
(r = sshpkt_get_u32(ssh, &max)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
goto out;
kex->nbits = nbits;
kex->min = min;
kex->max = max;
min = MAXIMUM(DH_GRP_MIN, min);
max = MINIMUM(DH_GRP_MAX, max);
nbits = MAXIMUM(DH_GRP_MIN, nbits);
nbits = MINIMUM(DH_GRP_MAX, nbits);
if (kex->max < kex->min || kex->nbits < kex->min ||
kex->max < kex->nbits || kex->max < DH_GRP_MIN) {
r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
goto out;
}
/* Contact privileged parent */
kex->dh = mm_choose_dh(min, nbits, max);
if (kex->dh == NULL) {
(void)sshpkt_disconnect(ssh, "no matching DH grp found");
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
(r = sshpkt_put_bignum2(ssh, dh_p)) != 0 ||
(r = sshpkt_put_bignum2(ssh, dh_g)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
goto out;
/* Compute our exchange value in parallel with the client */
if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
goto out;
debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init);
r = 0;
out:
return r;
}
static int
input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
{
struct kex *kex = ssh->kex;
BIGNUM *dh_client_pub = NULL;
const BIGNUM *pub_key, *dh_p, *dh_g;
struct sshbuf *shared_secret = NULL;
struct sshbuf *server_host_key_blob = NULL;
struct sshkey *server_host_public, *server_host_private;
u_char *signature = NULL;
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t slen, hashlen;
int r;
debug("SSH2_MSG_KEX_DH_GEX_INIT received");
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error);
if ((r = kex_load_hostkey(ssh, &server_host_private,
&server_host_public)) != 0)
goto out;
/* key, cert */
if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
goto out;
if ((shared_secret = sshbuf_new()) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)
goto out;
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;
/* calc H */
DH_get0_key(kex->dh, &pub_key, NULL);
DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
hashlen = sizeof(hash);
if ((r = kexgex_hash(
kex->hash_alg,
kex->client_version,
kex->server_version,
kex->peer,
kex->my,
server_host_key_blob,
kex->min, kex->nbits, kex->max,
dh_p, dh_g,
dh_client_pub,
pub_key,
sshbuf_ptr(shared_secret), sshbuf_len(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, DH pubkey 'f' and signed H */
if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
(r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
(r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */
(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));
DH_free(kex->dh);
kex->dh = NULL;
BN_clear_free(dh_client_pub);
sshbuf_free(shared_secret);
sshbuf_free(server_host_key_blob);
free(signature);
return r;
}
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