Serial Numbers

I want to use serial/registration numbers for my app with different licenses with validation. Ex. I assign Trial license with this algorithm, app validates it as trial number. Could someone point me in the right direction, and by the way, im not going to buy somethinbg to do it. Could someone show me some code?

there are programs designed to create algorithms for encrypting in different keys and based on different lengths/bases. Some of them can do RSA and hex encryption, and the like. I don't know the names of any of the current ones, but they are available for purchase. What you might want to do, if you don't want to waste time, is create an RSA encryption class for each type of password you want to create. Although, that leaves your encrypt/decrypt very much open to a well versed hacker.