In the not too distant past there was a fad for collectible trading card games, the most famous of which was Magic, The Gathering (tm). These

Oy, don't mention that name. I spent waaay too much money on cards (Ah, my foolish youth. Anyone want to buy a slightly used Chaos Orb? :).

games combined the collecting and trading of baseball cards with traditional aspects of card playing. Cards were issued by a central authority/publisher (Wizards of the Coast in the case of MtG). Each player uses his or her own deck; cards that are not played remain secret; however the same deck mut be used in each round of a match. tournament games are adjudicated by an umpire.

Design a set of crypto protocols to support the issuing, trading, and playing of such card games in real time (100ms compute time per move)

Well, here goes nothing for the playing part: Each player should submit a signed copy of their deck (i.e. a listing of all the cards therin) to the umpire (if you don't want the even umpire seeing the deck contents until afterwards, make them submit a bit-committed symetric key and encrypt the deck manifest with it). Each individual card in the deck should have a unique identifier which should be noted on the manifest. Identifiers wouldn't need to be sequential (in fact they might leak info to the opponent if they were), but duplicates of the same card should each have its own id. Depending on how you want to run things, you could allow (and probably should require) players to submit new a ID->card list before each round begins. So my deck might look like: ID Card -------------------- 309487 Prodigal Sorcerer 008461 Land (Plains) 663542 Land (Forrest) .... Before each round, opponents would exchange lists of card IDs. Whenever a player needs to "draw", the other player takes an ID at random off the list of IDs (and marks is as "used"). At the end of each round the players submit a transcript of the game to the umpire who then checks that all the cards played were in the decks, that no duplicates of the same id/card were used, or changes of cards (i.e. ID 440315 was supposed to be a "Zombie" but the owning player said it was a "Yawgmoth's Daemon"). If you want to do away with the umpire (for casual play between two people), have opponents swap the encrypted deck manifest and bit commit to key used. Afterwards they can double check for cheating themselves. Something you might want to allow is letting a player include extra IDs which map to "no card, pick again". This would allow players to disguise the exact size of their deck (although this would only allow for puffing up a deck, not making it appear smaller). As for issuing and trading cards, maybe store cards as signed certificates (something along the lines of "card name & serial number" signed by the owner, then by the issuer). This would make trading a bit of a problem as you couldn't give the card away without the issuer (Online clearing for Magic cards? :). And there's the problem of how do you tell who actually owns the card (if the issuer keeps a list of serial number->owners that might work, but again that needs online clearing). I missed all the discussion on digital bearer bonds a while back, but something like that might could be applied here. Don't know if that's what you were looking fore, but it's all I can think of at this late hour and I'm sure someone will shoot holes all through it anyhow. :) What do you think, sirs? --- Fletch __`'/| fletch@ain.bls.com "Lisa, in this house we obey the \ o.O' ______ 404 713-0414(w) Laws of Thermodynamics!" H. Simpson =(___)= -| Ack. | 404 315-7264(h) PGP Print: 8D8736A8FC59B2E6 8E675B341E378E43 U ------