I am a lazy programmer and I used the JEDI Serial thingy. I have made some changes to the source so that it is not the same as everyone else's.

I have in the past used Blowfish technology. The client when registering gives a number generated by the app based on hd serial and other unique stuff. That number is used to encrypt the serial key. If anything changes then the key is not decrypted and the software becomes demo again.

Software I wrote years ago used to sell thousands of copies and there were cracks all over the place. Then I started using moneypump (out of business now) and have never seen a crack or keygen for that version.

Craig