Provably fair gambling



A feature of crypto is not having to trust anyone, and therefore not being able to be cheated by anyone. So it is appropriate that crypto gambling operators are pioneering ways to provide trustless, provably fair gambling where they can’t cheat the players.

Provably fair gambling does not depend on cryptocurrency, it is just as easy for government currency operators to implement.


First let’s define a couple of words in the limited sense in which they are used in this article.

Hashes: A long string of characters derived from other data. This is a mathematical problem that is extremely difficult to solve but when solved it gives the data it hashes. If a solution is presented it is easy to backward test it to see if the solution is correct. So hashes are hard to solve but easy to verify a solution for.

Seeds: Extra data (a string of characters) applied to the hash which modifies what it hashes.

Provably fair casino games

Consider a card game that requires a random shuffle, such as blackjack. The idea is to stop the casino deciding what the card will be, or knowing what the card will be before it is dealt. The online equivalent of cutting the deck, and no dealing from the bottom of the deck.

The provably fair way to do this is

Step 1: The site shuffles the deck as normal.

Step 2: The site provides you with a hash of the shuffle.

Step 3: You provide a random seed, manually or automatically generated, that the site cannot see or predict. This is done client side in your browser, not on the site’s server.

Step 4: Your seed changes the shuffle to something neither you nor the site can have known. This is the online equivalent of cutting the deck to the dealers shuffle.

Verification part 1: After the hand is dealt the initial deck is laid out and you can check that the deck started out as the hash the site provided indicated.

Verification part 2: The final deck is laid out so you can check that the initial deck was changed in accordance with the seed you provided.

If that all checks out then there was no funny business and you have just played a provably fair hand!

If you are a visual learner these concepts are displayed with pictures here or a more detailed and technical explanation can be found here.

The same applies to games that require a random number such as roulette. This can all happen in the background without you realizing it, or you can use third party online tools such as quickhash.

If you are cryptography and code literate you can check it for yourself by following these instructions. If that is not your idea of fun then you could rely on independent trustworthy experts that have done the verification for us. But then we are back to trusting someone which is what we are trying to avoid.

Provably fair gambling is brilliant to have happening in the background but is too complicated to be useful for the masses, especially since you still have to trust the operator (such as allowing you to withdraw). But this is a new application of the technology so we can expect awareness to grow and usability in improve with time.

Provably fair sports betting

Fixed odds sportsbooks have always been provably fair in that they do not determine the result of the bet, or know it in advance. If they pay you the odds they said they would then they must be fair.

On the other hand totalizers could be cheating their customers by not paying out the advertised % of the pool to the winners as only they know how much was bet and how much gets paid out.

Crypto solves this problem by allowing bets to happen on the blockchain therefore allowing anyone to check how much was in the pool and match that against how much was paid out.

Provably fair sites could still rip you off

A site with provably fair games could still take your funds or sell your IP address and log in details to hackers; such incidents occur more often than rigged games. Value provably fair games but also follow these common sense tips to avoid crypto gambling scams.

I would rather bet with a known and trustworthy casino such as Cloudbet (review, bettors are geo-blocked) that do not yet provide provably fair games than an unknown and shady casino that does. Luckily we have , an all round high quality and trustworthy crypto casino where all the games are beautiful and provably fair.

Soon enough cryptography and multi-sig architecture will provide us with end to end trustless gambling services, oh and they will also have 0% house edge. A great example of how crypto values are changing the online landscape and soon the world!


  1. HypnoticGuy

    The term “Provably Fair” is very misleading, and the gambling sites who use it know exactly how it is misleading.
    When most English speaking people think of a game being “fair” it means to them that what they will be paid out for a win is going to be equal to the actual odds of the game.
    For example, a friend comes to me and says he wants to play a game with me for money. He says he will flip a coin and for every “heads” flip he will pay me $1. For every “tails” flip I will pay him $1. That is “fair”.
    if that same friend were to come to me and say He wants to play a game where every “heads” flip I will pay him $1 but for every “tails” flip he would pay me 50 cents, my reply would be “No way! That’s not FAIR”.
    Now it is true that with block chain verification if the games, bitcoin gambling sites can be considered “provably HONEST”, however if you are not being paid out in an amount that equals the actual odds of the game, it is not really “fair” no matter what the block chain says.
    The term “provably fair” seems to have become a bitcoin gambling standard, but not all people really understand what it implies. Thus as bitcoin becomes more accepted, and more people start gambling on these sites, the more some people will be misled.
    In fact, i wouldn’t be surprised if at some point in time someone brings a law suit against one of these gambling sites when they lose big, and then realize the odds were not in their favor, and thus the game did not meet the commonly accepted definition of fair.

    • John

      Provably fair shows that the operator is not cheating by changing the results of the game. It’s up to you, the player, to make sure you’re getting the best odds.
      If you were playing on American roulette and you lost, would you file a lawsuit because it has worse odds than European roulette?
      This article explained it pretty well about how you could get ripped off basically, the casino could choose not to pay you at all, or they could make the odds worse like what you described.
      By the way, can you give an example of a casino that does what you said (wants to play a game where every “heads” flip I will pay him $1 but for every “tails” flip he would pay me 50 cents)?

      • HypnoticGuy

        I am really sorry but that sounds like provably honest to me, not provably fair. If the issue is whether or not the operator is changing the results of the game then the issue is whether or not the operator is being honest.
        You wrote – “If you were playing on American roulette and you lost, would you file a lawsuit because it has worse odds than European roulette?” No, because the casino does not claim that their game is “fair”.
        Your mentioning casinos just won my argument for me. Do you know of any live casino that advertises their games as being “fair”? Don’t you think they would if they could?
        The way bitcoin casinos use the word “fair” is intentionally misleading.

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