Every player encrypts and shuffles every card
You encrypt and shuffle each card of the deck on your computer. This ensures that no one - not even us - can see your cards or manipulate the dealing of the cards.
You verify the correctness of the game on your computer
The entire poker protocol runs on the client side (your browser). This means that if any player tries to manipulate the card dealing he will be caught by you and reported.
Attempts at disrupting the game are penalized
When a player enters a table, he puts down a variable security deposit. If this player attempts to disrupt the poker protocol he loses a part his deposit.
FAQ & Details.
For the game to be "provably fair" should't it be on the blockchain?
No. Blockchains are extremely slow and inefficient. Provably fair means that you can yourself verify the fairness of the game - you don't need a blockchain for that. By using cryptography only where it is needed we achieve great performance and efficiency, while still keeping the game fair.