A student of mine alerted me to the following videos that describe some cryptographic protocols including some that are quantum. In particular, they demonstrate some ‘games’ that can be ‘won’ with a quantum system but not with a classical system. The videos are by a German hacker group know as the Chaos Computer Club.
A further description of some interesting protocols as given by my student:
“Off the Record” (software) and the “Dining Cryptographers” protocol are cryptographic systems which are pretty much the opposite of “normal” crypto. For example, crypto is usually used to make sure that no one can read the data sent, and that no one can later forge documents using the same key. OTR, on the other hand, publishes *all* the keys used as soon as the conversation is over, ensuring that any message produced later as “evidence” could just as easily have been forged, granting the users plausible deniability.
The Dining Cryptographers protocol is a cryptosystem that ensures a level of anonymity for the sender(s). As far as I know it has not yet been seriously implemented, but the original idea goes like this: Some cryptographers are having dinner out together. When it’s time to pay the bill, the waiter says the meal is already paid for. Now, the cryptographers respect the donor’s anonymity, but they would like to know whether the person who paid is one of their group, or someone else. To do this, each person sitting at the table creates a random number and secretly shows it to the person on his right. The difference between one’s own number and the number of the person to one’s left is the key. The key is xor’d with the message (in this case just one bit, yes/no) and the result is published. The sum of all published numbers is the message. In this case, 1 means someone at the table paid, 0 means no one there did. (Note this requires at least three participants!)
The last videois a cursory introduction to quantum information, but it has a couple of cool games that can be “won” with entanglement that can’t be solved classically.
Add to this the Hat game in which three people agree on colored hats. We discussed this one in class today and I may write up a little something on it since I think one might be able to make a Bell inequality out of the classical case.