How do I make a game with a serial key thing?

I am making a game that you need to purchase to play the full version,and I wanted to know,how do you make a key for the person who bought it?I'd really appreciate it.



P.S. I also want to know how to make it when they activate it they get the full game.

And I don't know if it works,but I am making the game with Game Maker 7.How do I make a game with a serial key thing?The easiest way is to use a simple password. At some point in the game play, ask for a password. If they have it, they can move on to the next level, and if they don't, refuse to move forward.



When somebody purchase the game, they're actually just purchasing the password. They already have the full game, but they cannot access it until they know the password.



Of course, the password will get around and people will be able to defeat this system. You could make it a little more secure by giving each instance of the game a unique serial number, and then requiring the users to send you the serial # to request a password. You then use the serial as a hash for MD5 or some other security protocol, and generate a custom password for that particular instance. It's probably not worth the effort.



Unless your game is really amazing, you should probably just give it away. People aren't buying games that are just like games they can play for free with Flash (and it's hard to do much more with GM.) It will probably be better in the long run if you give the game away and make a name for yourself so eventually you can sell games written in more substantial environments.