/*
* Diffie-Hellman-Merkle key exchange (client side)
*
* Copyright (C) 2006-2010, Brainspark B.V.
*
* This file is part of PolarSSL (http://www.polarssl.org)
* Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
*
* All rights reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#ifndef _CRT_SECURE_NO_DEPRECATE
#define _CRT_SECURE_NO_DEPRECATE 1
#endif
#include <string.h>
#include <stdio.h>
#include "polarssl/net.h"
#include "polarssl/aes.h"
#include "polarssl/dhm.h"
#include "polarssl/rsa.h"
#include "polarssl/sha1.h"
#include "polarssl/havege.h"
#define SERVER_NAME "localhost"
#define SERVER_PORT 11999
int main( void )
{
FILE *f;
int ret, n, buflen;
int server_fd = -1;
unsigned char *p, *end;
unsigned char buf[1024];
unsigned char hash[20];
havege_state hs;
rsa_context rsa;
dhm_context dhm;
aes_context aes;
memset( &rsa, 0, sizeof( rsa ) );
memset( &dhm, 0, sizeof( dhm ) );
/*
* 1. Setup the RNG
*/
printf( "\n . Seeding the random number generator" );
fflush( stdout );
havege_init( &hs );
/*
* 2. Read the server's public RSA key
*/
printf( "\n . Reading public key from rsa_pub.txt" );
fflush( stdout );
if( ( f = fopen( "rsa_pub.txt", "rb" ) ) == NULL )
{
ret = 1;
printf( " failed\n ! Could not open rsa_pub.txt\n" \
" ! Please run rsa_genkey first\n\n" );
goto exit;
}
rsa_init( &rsa, RSA_PKCS_V15, 0 );
if( ( ret = mpi_read_file( &rsa.N, 16, f ) ) != 0 ||
( ret = mpi_read_file( &rsa.E, 16, f ) ) != 0 )
{
printf( " failed\n ! mpi_read_file returned %d\n\n", ret );
goto exit;
}
rsa.len = ( mpi_msb( &rsa.N ) + 7 ) >> 3;
fclose( f );
/*
* 3. Initiate the connection
*/
printf( "\n . Connecting to tcp/%s/%d", SERVER_NAME,
SERVER_PORT );
fflush( stdout );
if( ( ret = net_connect( &server_fd, SERVER_NAME,
SERVER_PORT ) ) != 0 )
{
printf( " failed\n ! net_connect returned %d\n\n", ret );
goto exit;
}
/*
* 4a. First get the buffer length
*/
printf( "\n . Receiving the server's DH parameters" );
fflush( stdout );
memset( buf, 0, sizeof( buf ) );
if( ( ret = net_recv( &server_fd, buf, 2 ) ) != 2 )
{
printf( " failed\n ! net_recv returned %d\n\n", ret );
goto exit;
}
n = buflen = ( buf[0] << 8 ) | buf[1];
if( buflen < 1 || buflen > (int) sizeof( buf ) )
{
printf( " failed\n ! Got an invalid buffer length\n\n" );
goto exit;
}
/*
* 4b. Get the DHM parameters: P, G and Ys = G^Xs mod P
*/
memset( buf, 0, sizeof( buf ) );
if( ( ret = net_recv( &server_fd, buf, n ) ) != n )
{
printf( " failed\n ! net_recv returned %d\n\n", ret );
goto exit;
}
p = buf, end = buf + buflen;
if( ( ret = dhm_read_params( &dhm, &p, end ) ) != 0 )
{
printf( " failed\n ! dhm_read_params returned %d\n\n", ret );
goto exit;
}
if( dhm.len < 64 || dhm.len > 256 )
{
ret = 1;
printf( " failed\n ! Invalid DHM modulus size\n\n" );
goto exit;
}
/*
* 5. Check that the server's RSA signature matches
* the SHA-1 hash of (P,G,Ys)
*/
printf( "\n . Verifying the server's RSA signature" );
fflush( stdout );
if( ( n = (int)( end - p ) ) != rsa.len )
{
ret = 1;
printf( " failed\n ! Invalid RSA signature size\n\n" );
goto exit;
}
sha1( buf, (int)( p - 2 - buf ), hash );
if( ( ret = rsa_pkcs1_verify( &rsa, RSA_PUBLIC, SIG_RSA_SHA1,
0, hash, p ) ) != 0 )
{
printf( " failed\n ! rsa_pkcs1_verify returned %d\n\n", ret );
goto exit;
}
/*
* 6. Send our public value: Yc = G ^ Xc mod P
*/
printf( "\n . Sending own public value to server" );
fflush( stdout );
n = dhm.len;
if( ( ret = dhm_make_public( &dhm, 256, buf, n,
havege_rand, &hs ) ) != 0 )
{
printf( " failed\n ! dhm_make_public returned %d\n\n", ret );
goto exit;
}
if( ( ret = net_send( &server_fd, buf, n ) ) != n )
{
printf( " failed\n ! net_send returned %d\n\n", ret );
goto exit;
}
/*
* 7. Derive the shared secret: K = Ys ^ Xc mod P
*/
printf( "\n . Shared secret: " );
fflush( stdout );
n = dhm.len;
if( ( ret = dhm_calc_secret( &dhm, buf, &n ) ) != 0 )
{
printf( " failed\n ! dhm_calc_secret returned %d\n\n", ret );
goto exit;
}
for( n = 0; n < 16; n++ )
printf( "%02x", buf[n] );
/*
* 8. Setup the AES-256 decryption key
*
* This is an overly simplified example; best practice is
* to hash the shared secret with a random value to derive
* the keying material for the encryption/decryption keys,
* IVs and MACs.
*/
printf( "...\n . Receiving and decrypting the ciphertext" );
fflush( stdout );
aes_setkey_dec( &aes, buf, 256 );
memset( buf, 0, sizeof( buf ) );
if( ( ret = net_recv( &server_fd, buf, 16 ) ) != 16 )
{
printf( " failed\n ! net_recv returned %d\n\n", ret );
goto exit;
}
aes_crypt_ecb( &aes, AES_DECRYPT, buf, buf );
buf[16] = '\0';
printf( "\n . Plaintext is \"%s\"\n\n", (char *) buf );
exit:
net_close( server_fd );
rsa_free( &rsa );
dhm_free( &dhm );
#ifdef WIN32
printf( " + Press Enter to exit this program.\n" );
fflush( stdout ); getchar();
#endif
return( ret );
}
