If you give people the code to execute it can be read. It is most easily read when you deliver source code as in Perl, however it is also most powerful then. My advice is to stop thinking about encryption. It is a never-ending vicious circle that just makes it more annoying for your customers. If you don't care about the code being readable at execute time, but just want to lock it until then, well then you can use one of the various encryption modules on CPAN and force your customer to unlock it. But then it runs and can be read obviously. The other possibility of course is for you not to deliver the code in the first place. Run a web service on your own server for those methods.