programs/pkey/rsa_decrypt.c

/*
 *  RSA simple decryption program
 *
 *  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/config.h"

#include "polarssl/rsa.h"

#if !defined(POLARSSL_BIGNUM_C) || !defined(POLARSSL_RSA_C) ||  \
    !defined(POLARSSL_FS_IO)
int main( void )
{
    printf("POLARSSL_BIGNUM_C and/or POLARSSL_RSA_C and/or "
           "POLARSSL_FS_IO not defined.\n");
    return( 0 );
}
#else
int main( int argc, char *argv[] )
{
    FILE *f;
    int ret, c;
    size_t i;
    rsa_context rsa;
    unsigned char result[1024];
    unsigned char buf[512];
    ((void) argv);

    ret = 1;
    if( argc != 1 )
    {
        printf( "usage: rsa_decrypt\n" );

#ifdef WIN32
        printf( "\n" );
#endif

        goto exit;
    }

    printf( "\n  . Reading public key from rsa_pub.txt" );
    fflush( stdout );

    if( ( f = fopen( "rsa_pub.txt", "rb" ) ) == NULL )
    {
        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 );

    /*
     * Extract the RSA encrypted value from the text file
     */
    ret = 1;

    if( ( f = fopen( "result-enc.txt", "rb" ) ) == NULL )
    {
        printf( "\n  ! Could not open %s\n\n", "result-enc.txt" );
        goto exit;
    }

    i = 0;

    while( fscanf( f, "%02X", &c ) > 0 &&
           i < (int) sizeof( buf ) )
        buf[i++] = (unsigned char) c;

    fclose( f );

    if( i != rsa.len )
    {
        printf( "\n  ! Invalid RSA signature format\n\n" );
        goto exit;
    }

    /*
     * Decrypt the encrypted RSA data and print the result.
     */
    printf( "\n  . Decrypting the encrypted data" );
    fflush( stdout );

    if( ( ret = rsa_pkcs1_decrypt( &rsa, RSA_PUBLIC, &i, buf, result,
                                   1024 ) ) != 0 )
    {
        printf( " failed\n  ! rsa_pkcs1_decrypt returned %d\n\n", ret );
        goto exit;
    }

    printf( "\n  . OK\n\n" );

    printf( "The decrypted result is: '%s'\n\n", result );

    ret = 0;

exit:

#ifdef WIN32
    printf( "  + Press Enter to exit this program.\n" );
    fflush( stdout ); getchar();
#endif

    return( ret );
}
#endif /* POLARSSL_BIGNUM_C && POLARSSL_RSA_C && POLARSSL_FS_IO */