Cyberdice (Transcript of Discussion)

The game itself is basically a very simple gambling game where you have people round the table with dice, and everyone has put some money on the table to play, the same amount for everybody. They've rolled the dice, and the one who gets the highest dice roll takes all the money that was on the table. (Imagine for the moment that nobody rolls the same value on the dice: you have dice with a very high number of sides so it's very unlikely that two people get the same number.) So the game is simplicity itself, each player rolls dice, winner takes all. But we are doing that in cyberspace and the `cyber' part means that there is no table to put the money on, or roll the dice on: all you see is that you have some network card out of which bits come, and into which you put bits, and all you hear about the other people is that bits come out of your network card. You don't know who they are, you don't know even if they are there, they could all be `sock-puppets' of someone else. And you have to deal with the issue of rolling dice fairly, and exchanging money, where all you know is these bits that come out of your network card. We've been talking a lot about modelling the adversary, and here, basically the adversary can do anything that you can do on bit strings. The network is not secure, this is essentially Dolev-Yao at full power. And then, on top of that, everyone else who is playing with you may be a crook, for all you know, because you don't know who they are. And also they may disobey the rules in the most inconvenient way, not just by doing something other than what the protocol says, but also by stopping responding when they're supposed to respond. Tuomas Aura: So they could be colluding? Reply: They could be colluding, yes, in fact everybody could be colluding against you. And the point is that you don't know if other players are in fact the same player, with di erent aliases for the same player. These are the peers of the peer-to-peer situation and any one of them can become the dealer if they like. It's something you decide, you wake up one morning and you decide I want to make some money, why don't I o er a game of Cyberdice. I'm o ering a game with these parameters. If you want to play with me then these are the rules. The dealer chooses the maximum number of players and if you want to play you must put up perhaps ¿5 as a player, and he says I will take up to 20 people which means the maximum win that you can make in this game is ¿100. Up