209 lines
6.1 KiB
C
209 lines
6.1 KiB
C
/* $OpenBSD: kexgexs.c,v 1.18 2014/01/12 08:13:13 djm Exp $ */
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/*
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* Copyright (c) 2000 Niels Provos. All rights reserved.
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* Copyright (c) 2001 Markus Friedl. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "includes.h"
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#include <sys/param.h>
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#include <stdarg.h>
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#include <stdio.h>
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#include <string.h>
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#include <signal.h>
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#include <openssl/dh.h>
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#include "xmalloc.h"
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#include "buffer.h"
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#include "key.h"
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#include "cipher.h"
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#include "kex.h"
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#include "log.h"
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#include "packet.h"
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#include "dh.h"
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#include "ssh2.h"
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#include "compat.h"
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#ifdef GSSAPI
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#include "ssh-gss.h"
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#endif
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#include "monitor_wrap.h"
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void
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kexgex_server(Kex *kex)
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{
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BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
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Key *server_host_public, *server_host_private;
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DH *dh;
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u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
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u_int sbloblen, klen, slen, hashlen;
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int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1;
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int type, kout;
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if (kex->load_host_public_key == NULL ||
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kex->load_host_private_key == NULL)
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fatal("Cannot load hostkey");
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server_host_public = kex->load_host_public_key(kex->hostkey_type);
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if (server_host_public == NULL)
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fatal("Unsupported hostkey type %d", kex->hostkey_type);
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server_host_private = kex->load_host_private_key(kex->hostkey_type);
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type = packet_read();
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switch (type) {
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case SSH2_MSG_KEX_DH_GEX_REQUEST:
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debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
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omin = min = packet_get_int();
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onbits = nbits = packet_get_int();
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omax = max = packet_get_int();
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min = MAX(DH_GRP_MIN, min);
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max = MIN(DH_GRP_MAX, max);
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nbits = MAX(DH_GRP_MIN, nbits);
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nbits = MIN(DH_GRP_MAX, nbits);
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break;
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case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
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debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
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onbits = nbits = packet_get_int();
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/* unused for old GEX */
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omin = min = DH_GRP_MIN;
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omax = max = DH_GRP_MAX;
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break;
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default:
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fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
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}
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packet_check_eom();
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if (omax < omin || onbits < omin || omax < onbits)
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fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
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omin, onbits, omax);
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/* Contact privileged parent */
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dh = PRIVSEP(choose_dh(min, nbits, max));
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if (dh == NULL)
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packet_disconnect("Protocol error: no matching DH grp found");
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debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
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packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
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packet_put_bignum2(dh->p);
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packet_put_bignum2(dh->g);
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packet_send();
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/* flush */
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packet_write_wait();
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/* Compute our exchange value in parallel with the client */
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dh_gen_key(dh, kex->we_need * 8);
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debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
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packet_read_expect(SSH2_MSG_KEX_DH_GEX_INIT);
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/* key, cert */
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if ((dh_client_pub = BN_new()) == NULL)
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fatal("dh_client_pub == NULL");
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packet_get_bignum2(dh_client_pub);
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packet_check_eom();
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#ifdef DEBUG_KEXDH
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fprintf(stderr, "dh_client_pub= ");
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BN_print_fp(stderr, dh_client_pub);
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fprintf(stderr, "\n");
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debug("bits %d", BN_num_bits(dh_client_pub));
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#endif
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#ifdef DEBUG_KEXDH
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DHparams_print_fp(stderr, dh);
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fprintf(stderr, "pub= ");
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BN_print_fp(stderr, dh->pub_key);
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fprintf(stderr, "\n");
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#endif
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if (!dh_pub_is_valid(dh, dh_client_pub))
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packet_disconnect("bad client public DH value");
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klen = DH_size(dh);
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kbuf = xmalloc(klen);
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if ((kout = DH_compute_key(kbuf, dh_client_pub, dh)) < 0)
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fatal("DH_compute_key: failed");
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#ifdef DEBUG_KEXDH
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dump_digest("shared secret", kbuf, kout);
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#endif
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if ((shared_secret = BN_new()) == NULL)
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fatal("kexgex_server: BN_new failed");
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if (BN_bin2bn(kbuf, kout, shared_secret) == NULL)
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fatal("kexgex_server: BN_bin2bn failed");
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memset(kbuf, 0, klen);
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free(kbuf);
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key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
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if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
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omin = min = omax = max = -1;
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/* calc H */
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kexgex_hash(
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kex->hash_alg,
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kex->client_version_string,
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kex->server_version_string,
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buffer_ptr(&kex->peer), buffer_len(&kex->peer),
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buffer_ptr(&kex->my), buffer_len(&kex->my),
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server_host_key_blob, sbloblen,
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omin, onbits, omax,
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dh->p, dh->g,
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dh_client_pub,
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dh->pub_key,
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shared_secret,
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&hash, &hashlen
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);
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BN_clear_free(dh_client_pub);
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/* save session id := H */
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if (kex->session_id == NULL) {
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kex->session_id_len = hashlen;
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kex->session_id = xmalloc(kex->session_id_len);
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memcpy(kex->session_id, hash, kex->session_id_len);
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}
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/* sign H */
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kex->sign(server_host_private, server_host_public, &signature, &slen,
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hash, hashlen);
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/* destroy_sensitive_data(); */
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/* send server hostkey, DH pubkey 'f' and singed H */
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debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
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packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
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packet_put_string(server_host_key_blob, sbloblen);
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packet_put_bignum2(dh->pub_key); /* f */
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packet_put_string(signature, slen);
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packet_send();
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free(signature);
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free(server_host_key_blob);
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/* have keys, free DH */
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DH_free(dh);
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kex_derive_keys_bn(kex, hash, hashlen, shared_secret);
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BN_clear_free(shared_secret);
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kex_finish(kex);
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}
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