Bitcoin Forum

Originally from http://www.bitcoin-casino-guide.com/provably-fair-gambling/

TL;DR

The provably fair way for a site to deal cards is for the site to shuffle the deck as normal then provide you with a hash of the shuffle. As a card is dealt you provide a random seed, manually or automatically generated in your browser (client side, not on the sites server) that the site cannot see or predict. Your seed changes the card to something neither you nor the site can have known. This is the online equivalent of cutting the deck to the dealers shuffle.

After the hand is dealt the deck is laid out and you can check that the deck started out as the hash the site provided indicated and that the cards were then changed in accordance with the seed you provided. If these are both the case then you have just played a provably fair hand!

See link for more details and explanation.

pretty much word for word from the bitzino provably fair FAQ and your TL;DR = TL;SDR

here is mine.

• Dealer hashes (deck order + dealer seed).
• client provides random seed for shuffler
• deck is shuffled with clients seed

Once original deck order and dealer seed is shown, check hash(deck order + dealer seed) against the hash you were shown, then shuffle the deck with the clients seed and check against the cards dealt.

:P

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Still reading ? cool then lets discuss some details:

Q> Why does the dealer need a random seed ?
A> Well if he didnt seed the hash, you could create a hash table of every deck combination then when playing simply look up the deck order using the hash then shuffle it using your seed and you will know the order of the deck.

Q> Whats so important about a client seed.
A> without this its not provably fair, its only provable results.

Q> Can I trust the site to generate my seed for me every time.
A> No, you should use your own RNG or at the very least verify their RNG is actually a RNG.
Let me put it another way, would you let the dealer cut the deck for you ? if not, then you should be setting your own seeds using your own RNG or ensuring the client side RNG is what it claims to be.

You are describing this in a confusing way. You should write that the seed is used to reshuffle (or as part of a single shuffle) before the card is dealt.

agreed that is definitely not the correct way to describe.

you provide the seed BEFORE any cards are dealt because the seed is used to reshuffle the deck.

Thanks guys, I made that change. Seems like it should happen as cards are dealt so the house does not know what the card will be. The way you describe it can the house see the deck after you provide the seed but before they deal?

The deck (we called it the "Initial Shuffle") is already determined BEFORE the game started (at the end of previous game) and before the players enter their player seed.

To show that the "initial shuffle" wasn't change AFTER the players entered their player seed, we provide a one way hash (SHA-256) of the deck before the game, which is verifiable after the game ends.

For more details, you can read it here: https://coinroyale.com/provablyfair

Or you're free to ask/PM me any questions about Provably Fair in general..

That is already understood and explained. I was talking about when the clients seed is provided and changes the card from what the initial shuffle was.

I had thought it was as the card was dealt so the operator can not know what would be dealt. But then others said that was not the case. I guess as long it its happening client side and the operator can't see what the deal will be before the deal its not relevant. 

Im just going to go ahead and say it.

You shouldnt explaining provably fair gambling when its clear you need it explained to yourself.
There is enough ignorance and misinformation around already.

OP or mods should rename the thread title.

I'd like to ask if it's possible to have a possibly fair process without the initial shuffle.

It seems that while the initial shuffle's order is irrelevant, the initial shuffle is still necessary.. Why?

Also for operators, do you use a "fresh deck" for every shuffle or do you use the previous deck to start the shuffle for the next deck?  The final result shouldn't matter if the RNG is good but want to see what others do.

Yes it is.
You would show a hash of the servers secret, then shuffle the deck using the (client seed + servers seed).


Its not, bitzino does this as at a casino we expect a shuffled deck + player cut.
Bitzino does better than a phsyical casino but doing the dealer shuffle then the player shuffle.


All sites Ive played use a new deck each hand, so good luck counting cards :(

Yeah totally.  Especially blackjack, they reshuffle after every hand.  This actually lowers house edge a slight bit tho playing basic strategy vs. playing basic strategy without reshuffling every hand.  (ie no card counting involved in either scenario)

But what i meant is that provable fair shuffle flow seems to be like this.

Deck  -shuffle-> Initial Shuffle -shuffle-> final shuffle

where the first shuffle only uses a standard shuffle algo, and the 2nd uses the seeds provided by client and server.

Do operators use input a fresh deck for "Deck" every time, or do they use the previous decks order?  although ultimately, it doesn't matter, if the RNG to create the initial shuffle is 100% fair.

Yes, they use a fresh deck each time.

If they did not change their shuffle each time and only shuffled on the clients seed then the client would entirely control the deck order and be able to reuse old seeds.