http://www.google.com/search?hl=en&i...authentication

its just like a checksum I think, you basically have your key that you feed in and you could match up the checksum of this with one stored on your computer.

or you could have something similar to that you do with encryption, you feed it the key it then uses the public key to turn something into plain text or it could remain cipher text, thus allowing it to be checked and authenicated.

think about it, what does a real key do in real life on your front door?

i2c