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/* $OpenBSD: kexgexc.c,v 1.37 2021/01/31 22:55:29 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 "includes.h"
#ifdef WITH_OPENSSL
#include <sys/types.h>
#include <openssl/dh.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include "openbsd-compat/openssl-compat.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"
#include "compat.h"
#include "dispatch.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "misc.h"
static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *);
static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *);
int
kexgex_client(struct ssh *ssh)
{
struct kex *kex = ssh->kex;
int r;
u_int nbits;
nbits = dh_estimate(kex->dh_need * 8);
kex->min = DH_GRP_MIN;
kex->max = DH_GRP_MAX;
kex->nbits = nbits;
if (ssh->compat & SSH_BUG_DHGEX_LARGE)
kex->nbits = MINIMUM(kex->nbits, 4096);
/* New GEX request */
if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
(r = sshpkt_put_u32(ssh, kex->min)) != 0 ||
(r = sshpkt_put_u32(ssh, kex->nbits)) != 0 ||
(r = sshpkt_put_u32(ssh, kex->max)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
goto out;
debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
kex->min, kex->nbits, kex->max);
#ifdef DEBUG_KEXDH
fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
kex->min, kex->nbits, kex->max);
#endif
debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
&input_kex_dh_gex_group);
r = 0;
out:
return r;
}
static int
input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh)
{
struct kex *kex = ssh->kex;
BIGNUM *p = NULL, *g = NULL;
const BIGNUM *pub_key;
int r, bits;
debug("SSH2_MSG_KEX_DH_GEX_GROUP received");
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, &kex_protocol_error);
if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 ||
(r = sshpkt_get_bignum2(ssh, &g)) != 0 ||
(r = sshpkt_get_end(ssh)) != 0)
goto out;
if ((bits = BN_num_bits(p)) < 0 ||
(u_int)bits < kex->min || (u_int)bits > kex->max) {
r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
goto out;
}
if ((kex->dh = dh_new_group(g, p)) == NULL) {
r = SSH_ERR_ALLOC_FAIL;
goto out;
}
p = g = NULL; /* belong to kex->dh now */
/* generate and send 'e', client DH public key */
if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
goto out;
DH_get0_key(kex->dh, &pub_key, NULL);
if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
(r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
goto out;
debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
#ifdef DEBUG_KEXDH
DHparams_print_fp(stderr, kex->dh);
fprintf(stderr, "pub= ");
BN_print_fp(stderr, pub_key);
fprintf(stderr, "\n");
#endif
debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
r = 0;
out:
BN_clear_free(p);
BN_clear_free(g);
return r;
}
static int
input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh)
{
struct kex *kex = ssh->kex;
BIGNUM *dh_server_pub = NULL;
const BIGNUM *pub_key, *dh_p, *dh_g;
struct sshbuf *shared_secret = NULL;
struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
struct sshkey *server_host_key = NULL;
u_char *signature = NULL;
u_char hash[SSH_DIGEST_MAX_LENGTH];
size_t slen, hashlen;
int r;
debug("SSH2_MSG_KEX_DH_GEX_REPLY received");
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &kex_protocol_error);
/* key, cert */
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 ||
(r = kex_verify_host_key(ssh, server_host_key)) != 0)
goto out;
/* DH parameter f, server public DH key, signed H */
if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 ||
(r = sshpkt_get_string(ssh, &signature, &slen)) != 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_server_pub, shared_secret)) != 0)
goto out;
if (ssh->compat & SSH_OLD_DHGEX)
kex->min = kex->max = -1;
/* calc and verify 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->my,
kex->peer,
server_host_key_blob,
kex->min, kex->nbits, kex->max,
dh_p, dh_g,
pub_key,
dh_server_pub,
sshbuf_ptr(shared_secret), sshbuf_len(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));
DH_free(kex->dh);
kex->dh = NULL;
BN_clear_free(dh_server_pub);
sshbuf_free(shared_secret);
sshkey_free(server_host_key);
sshbuf_free(tmp);
sshbuf_free(server_host_key_blob);
free(signature);
return r;
}
#endif /* WITH_OPENSSL */
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