Provably fair

The technique we use in our provably fair blackjack game will mathematically guarantee we can not cheat the game and it is always a fair random dealt game. How do we do this? Let's take a random example:

1. Before each game (after ending a previous game), the server generates a new random serverseed which is kept secret.
2. To prove we will not change this serverseed, we already provide you with the SHA512 hash of this seed. In the console log you will see
   

   New server seed hash for next game: b050051e1a9cb37a9d31c613ba6ee6f09c2a0a676fbda86c7dfb86a5c73bba5b41c1e2cd77fe26734315cd5c260e36f78317281a4cf304f3e8e62e2e0559a5ff

3. You press 'deal' to start a new game. Your browser will generate a random clientseed (see JS source), which will be provided to our backend and also printed in the console log:
   

   Generated new clientseed (local): 88165868741

4. Our backend will now salt and concatenate it's serverseed and your clientseed ('satoshi' + serverseed + clientseed). The serverseed (which is not yet revealed) is LNBJd539a0edb1d6f32f47b441afdcd3b06f994b2890253b3e95, so when we concatenate everything, we get satoshiLNBJd539a0edb1d6f32f47b441afdcd3b06f994b2890253b3e9588165868741.
5. The server will now SHA512 this concatenated seeds. You can try this yourself using any online tool (example). The SHA512 of this concatenation is cf17181cdce1494e8f4902023a9bc626d36496e01c18fd2c3dfffec44b7a6a72473cfe72d6a861a7aa69d0e7ccfc313d57dae8fbac22866efd37b06dbc6ddb66.
6. This string decides the order of the deck. Split in chunks of two characters: cf, 17, 18, 1c, dc, e1, 49, ...
7. Now you can look up these codes in the below table. You could also convert these HEX groups to decimal to find their sequence number. Eg: cf=207, 17=23, 18=24 ..
8. Attention: if a number is higher than 207 (CF in hex), it is ignored. If it comes multiple times, it is ignored as well since the card is already taken from the deck. In the above example the hex groups 'dc' en 'e1' would be ignored because too high.
9. The order of our shuffled deck is thus: king of clubs, jack of hearts, queen of hearts, 3 of diamonds, 9 of hearts, ...
10. We always deal in this order: player card 1, dealer (downcard), player card 2, dealer (upcard), player cards until stand or 21, dealer cards 3-n. In this example, it means the player will get dealt the king and queen, and the dealer has the jack (downcard) and 3 (upcard). The player has thus 20 and can now choose to stand or hit. If the player hits, he will get the next card in the deck but given his cards, he stands. Now the dealer, who has a 13, hits and gets the 9 of hearts. This gives him a total of 22, so the player wins!
11. The game has ended, so we can safely expose our serverseed:
    

    The server seed was: LNBJd539a0edb1d6f32f47b441afdcd3b06f994b2890253b3e95

12. You can now totally verify there was no way we could have reshuffled the deck in our favor. When you take the SHA512 of the given serverseed, you will get b050051e1a9cb37a9d31c613ba6ee6f09c2a0a676fbda86c7dfb86a5c73bba5b41c1e2cd77fe26734315cd5c260e36f78317281a4cf304f3e8e62e2e0559a5ff. This is exactly what we've shown you before the game started, so our server seed was already determined at that point. Since your browser only created a random client seed after we've shown this hash, there was no way for us to cherry-pick a better serverseed.

This is a layout of the deck we use.