Cryptography Wedding Ring Contest!

Cory Doctorow, scifi writer and editor of BoingBoing.net, is a lover of things clever, cryptic, and steampunk. He's also Canadian, which warms my maple leaf heart.

He's running a contest for people to design uses for the cryptography built into his wedding rings. "When my wife and I started to plan our wedding, we inevitably turned to the question of rings, and it was only a matter of time before we came to the idea of rings with little wheels on them that could be used as crypto devices, in the manner of super-duper Captain Midnight Decoder Badges. His Rules:

"Now it's time that we turn to the Internet with a challenge: given these two matching rings, what crypto applications can you come up with? Could you use them to scramble passwords (possibly hashed with a key)? How about encoding messages for secret transmission? What additional common apparatus (say, different-sized coins) could you use to generate initialization vectors and increase the system's security?

This is an open competition to be judged by Bruce "Applied Cryptography" Schneier and me -- the winner gets a copy of Little Brother signed by both of us. Post your submissions to the comments or send them to cryptocontest@craphound.com before Oct 1, 2008. (Go look at the nifty ring).