$function = Win32::API->new('NSLClientLibrary', 'XYZDecrypt', 'PPP', 'I');

sub call_function {
    my ($value, $key, $encrypted) = @_;
    # Here we pad $value to the expected length, to avoid a buffer overrun
    # I guess that the result is at most as long as the encrypted string
    $value = ' ' x length $encrypted;
    $function->( $value, $key, $encrypted );
    $value =~ s!\0.*!!; # we assume that the first \0 returned indicates end of the string
    return $value
};