Exactly, the factoring problem reduces to a secret that only you know. The awesome part is you can actually prove to the world that you know the secret without actually revealing the secret!

I only know of two generally accepted forms of authentication: knowledge of a secret (in many variations) and possession of an object (which many be your body). The idea of authenticating someone based on how the do something is really cool, but I've never seen it actually used. If you've heard of something similar used in practice, I would love to hear about it.

I wonder how consistent people really are and how quickly their skills change. It's like voice recognition: it seems like a great idea, but what if I have a cold?