Quote from: vlees on August 07, 2013, 03:35:01 PM

Quote from: Dabs on August 07, 2013, 01:41:21 PM

Ok, how do you fairly shuffle a deck, and provably show a player's own cards are fairly drawn, without showing other player's cards or hands? Poker specifically has this problem.

As I explained in my post: Fisher-Yates shuffle, create a string out of the deck, hash it. Show the hash beforehand, the entire deck afterwards.
Did you read my post?

But if you show the entire deck afterwards, and everyone knows the order the cards are handed out, everyone can know everyone else's hands. That's a problem in poker, if you do not want other players to know your cards even if you lost.

You only show your hand if you win. In fact, you don't need or you don't want to show your hand if you win because everyone else folded. However, you at least want to know that the cards you got were fairly given, and provably so.

The solution, I think is to hash each card and a nonce that indicates the position of that particular card in the deck. The player that holds the cards can see his own cards, but not the others, and can verify that his cards come from the deck in the order it was supposed to.

This is possible, but it might become unwieldy to verify. You have to create a hash for the shuffling seed, and a hash for each card. If you only use one deck, that is still 52 cards or 53 hashes. If you use multiple decks, that's a lot more hashes.

Also, it doesn't have to be Fisher-Yates, but any shuffling where everyone knows the procedure, that uses maybe SHA256 (as always) with random seeds that can be revealed after the game. (After reading about it, everything that can shuffle can fit into a Fisher-Yates variant or something similar.)

As far as players are concerned, it will be Provably Fair as well as Provable Results.

That still leaves the house being able to cheat by knowing all the cards and telling the players which cards they have. I'm not sure we can do anything about that. It's the same problem with dice sites. The owners (who know the server seeds) can play as a player and win or lose the game on purpose.