sub query_users {
    my ( $self, $filename ) = @_;

    my $func =
      import_api( 'advapi32', 'QueryUsersOnEncryptedFile', 'PP', 'N' );        
    die "Could not import API QueryUsersOnEncryptedFile: $!"
      unless defined $func;
      
    $filename = make_unicode( File::Spec->canonpath($filename) );   
    print "filename: $filename\n";

	my $encCertHashList = Win32::API::Struct->new( 'ENCRYPTION_CERTIFICATE_HASH_LIST' ); 	
	print "retval: " . $func->Call( $filename, $encCertHashList) . "\n";		
	print $encCertHashList->{nCert_Hash}, "\n";
	
	$encCertHashList = Win32::API::Struct->new( 'ENCRYPTION_CERTIFICATE_HASH_LIST' ); 	
	print "retval: " . $func->Call( $filename, \$encCertHashList) . "\n";
	print $encCertHashList->{nCert_Hash}, "\n";
	
	$encCertHashList = " " x 1024;
	print "retval: " . $func->Call( $filename, $encCertHashList) . "\n";
	print $encCertHashList, "\n";
	
	$encCertHashList = " " x 1024;
	print "retval: " . $func->Call( $filename, \$encCertHashList) . "\n";	
	print $encCertHashList, "\n";		
}