Provably Fair Blackjack

The concept of provably fair blackjack addresses one of the biggest concerns many players have always had about online casinos — that it seems all too easy for them to cheat. Of course, a brick and mortar casino can cheat in its games as well. There’s something about a casino that only exists in cyberspace, though, where virtual cards and dice are really just numbers inside a computer, that makes many people uneasy. When a string of bad luck hits, it’s easy to start wondering if the computer has been programmed to stack the odds against the players.

For some, inspections and licensing from regulatory organizations are enough to belay their doubts about any unfair play. Others though, don’t want to rely on the word of a third party. Just like they want to see the deck of cards laid out on a blackjack table before a game starts in a land-based casino, they want something tangible that they can verify themselves. They want real proof that the games they are betting on in online casinos are fair.

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What Is Provably Fair Blackjack?

The idea of provably fair gaming means that the outcome of a game, or series of games, is determined in a transparent way that allows the player to verify that the outcome was not unfairly altered in some way.

Provably Fair Blackjack Games

You’ve undoubtedly seen many different ways of doing this without even realizing it. Let’s take the lottery, for example. In order to prove that a lottery drawing is fair, most drawings involve putting numbered balls into some sort of mixer that makes it impossible for anyone to know in advance which number will be drawn. The winning numbers are then picked publicly, usually on live TV. Doing things this way provides transparency and proves to the audience that the drawing is fair and the results are not skewed in anyone’s favor.

Providing a provably fair blackjack game online is somewhat more complicated, but not as hard to do as you might think.

How Does Provably Fair Blackjack Work?

The basic process behind a provably fair blackjack game goes like this:

  1. The casino generates a random, secret string representing the result of a shuffled deck (or decks) of cards. This is often referred to as the “server seed”. This string is encrypted with a standard algorithm and given to the player before the game starts.
  2. The player is asked for a number or string that will be used with the casino’s string to generate a final result. This is often referred to as the “client seed”.
  3. The client seed and the server seed are combined to create a result for the game. For example, this step could decide where the shuffled deck is cut before the deal.
  4. When the game is over, the server seed is revealed, allowing the player to do his own calculations and verify that the game was fair.

How To Verify A Provably Fair Blackjack Game

All this talk of algorithms, encryption, and seeds might make this all sound overly complicated, but verifying the results of a provably fair blackjack game really isn’t too hard. Once you understand how all the pieces work together, it’s a quick and painless task.

The easiest way to explain how it works is to walk you through a simplified, but accurate, example. In the end, anything you do with an online casino is just the result of random numbers and mathematics. So let’s say that you and I are going to play a provably fair game where I will think of a random number and you will add your own number to it. You will then win the bet if you can guess the result of adding the two numbers together.

An Example Of a Provably Fair Game

The first thing we need to do is establish that I have a number in mind and that I cannot change it after you place your wager. To do this, I will think of a number (server seed) and encrypt it using the standard SHA256 hashing algorithm, which is commonly used for provably fair games. I will then give you the result of that encryption before you choose your number or make your bet.

I am going to choose the number 385. Using the SHA256 hash, I get a result (a hash) of:


The important thing to note here is that the SHA256 algorithm will always return the same result for the number 385. If I change any of the digits, the resulting hash will be different. It doesn’t matter if you’re encrypting one digit or one million. If a single character in the string changes, the resulting hash changes.

So now I pass to you the resulting hash. This lets you know that I have chosen a number without telling you what that number is. If you knew the number in advance, you could, of course, cheat on the bet yourself.

Now I ask you for the number you want to combine with my number (client seed), and what you think the result will be. Let’s say you’re a psychic freak of nature and you pick the number 115 and say the result will be 500. If I tell you that you’ve won you’re going to be happy, but what happens if I don’t want to pay off your bet and decide to cheat? What if I tell you that you were unbelievably close but my number was 382?

Since you have the hash that I gave you before we started, you can verify whether or not I’m telling the truth. You can simply go to any of the freely available SHA256 hash tools, get the results for my number and compare to the original hash. If you generate the hash for the number 382 you will get:


The original — so you don’t have to scroll back up — was:


You don’t have to examine every character in the two hashes to see that they are different. Since I gave you the original hash before we made any bets, it becomes obvious that somewhere after I took your money, I changed my number. I cheated and you can clearly see it. If the number I told you after the game was the same as the number I picked before the game, the two hashes would be identical.

This is exactly how a provably fair blackjack game works. The formulas a casino uses to create the shuffle of the cards or the result of the game might be different from one site to another, but any site that offers provably fair games will explain how results are determined and give you the information you need to verify results for yourself.

Provably fair blackjack games are not offered at many online casinos yet, but the number of casinos spreading these games is growing. Hopefully, in the future, provably fair games of all kinds will become the standard rather than the exception in online gambling.