There are a lot of questions relating to license keys asked on stackoverflow. But they don't answer this question.

Can anyone provide a simple license key algorithm that is technology independent and doesn't required a diploma in mathematics to understand ?

The license key algorithm is similar to public key encryption. I just need something simple that can be implemented in any platform .Net/Java and uses simple data like characters. Preferably no byte translations required.

So if a person presents a string, a complementary string can be generated that is the authorisation code. Below is a common scenario that it would be used for.

1. Customer downloads s/w which generates a unique key upon initial startup/installation.
2. S/w runs during trial period.
3. At end of trial period an authorisation key is required.
4. Customer goes to designated web-site, enters their code and get authorisation code to enable s/w, after paying :)

Don't be afraid to describe your answer as though you're talking to a 5 yr old as I am not a mathemtician. Just need a decent basic algorithm, we're not launching nukes...

NB: Please no philosophy on encryption nor who is Diffie-Hellman. I just need a basic solution.