The hash, the seed and the recalculation

Provably fair explained: what the check proves and what it does not cover

With a hash, two seeds and a counter you can recalculate a round after it has been played. Here is the procedure step by step, and where the limits of the check lie.

Provably fair is a method that lets you recalculate the result of a round in a house game. Before you play, the operator commits to a secret value by showing you a fingerprint of it. Once the value has been revealed, you can check for yourself that the fingerprint matches and that the outcome follows from the figures that were locked.

The arrangement is common in house games such as dice, crash, mines and plinko. It is useful, but it answers one particular question. This page explains which. Which operators actually show such a check can be seen in the full comparison on the home page of Kryptospill.

The three values that decide a provably fair round, and the check you can make afterwards. The check shows that the round was not altered; it says nothing about the house edge, the caps or the payout.

The building blocks: four terms

Four terms recur, whichever operator or studio you look at:

The server seed. A random string of text the operator makes and keeps secret while it is in use.
The hash. A digital fingerprint of the server seed, usually made with SHA-256. The fingerprint is shown before you play. It is practically impossible to work backwards from the hash to the seed, but simple to check that a seed gives exactly that hash.
The client seed. A value from your side. It is often made automatically, but in many games you can change it yourself.
The nonce. A counter that rises by one for every round you play with the same pair of seeds.

The combination of the server seed, the client seed and the nonce gives one figure per round. That figure is translated into an outcome: a dice value, a crash point, the placement of mines or the path of a ball.

Step by step: how the check works

The operator makes a server seed and shows you the hash of it.
You have a client seed. Change it to something you have chosen yourself.
You play. For every round the nonce rises by one, and the outcome is worked out from the three values.
You ask for a new server seed. The operator then reveals the old one and makes a new one, with a new hash.
You check the hash. Run the revealed server seed through SHA-256 and see that the result is identical to the hash you got before you played.
You work out the rounds. With the server seed, the client seed and the nonce you can recreate every outcome and compare it with the game history.

The point lies in the order. The hash was shown before the operator knew your client seed, and the server seed could not be swapped without the hash changing. So neither party can have steered the outcome afterwards.

A worked example

The figures below were made by us to show the principle. The method varies between operators, so always use the description the game itself gives.

Server seed: 7b2e91c4d05a3f68. The hash with SHA-256 begins with b13ae8ac.
Client seed: kvelds-seed. Nonce: 1.
A common method is HMAC-SHA256 with the server seed as the key and «kvelds-seed:1» as the message. The result begins with 7dd980d1.
The first eight characters are converted from hexadecimal into an integer: 2,111,406,289.
Divided by 4,294,967,296 (all possible values with eight characters) that gives roughly 0.4916.
In a dice game with outcomes from 0 to 99.99 the round comes out at 49.16.

The same figure can be used in other ways. In plinko a value below 0.5 can mean left and a value above it right, row by row. The whole path down the board can be recalculated that way, as shown on the page about rows and cells.

Provably fair in four fields

The casino shows the hash of the server seed in advance, you choose the client seed, and the nonce rises by one per round. Change the seed and you get to see the old server seed and can check the hash yourself. The values in the figure are shortened examples.

An example from a studio: Aviator

Spribe describes the arrangement for Aviator on a page of its own about fairness (spribe.co/provably-fair, opened on 15 September 2026). It states that the operator makes a server seed of 16 random characters, and that the hash for the next round (SHA256) is shown in the player's «Provably Fair Settings» before the round. The client seeds come from the players. When the round starts, the server seed and the client seeds are combined and hashed with SHA512, and the result is derived from that hash. Each round can be checked from the game history through an icon of its own, and the player can change their client seed.

So here several players' seeds go into the same round, because everyone sees the same plane. More on the game itself is in the walk-through of Aviator.

What the operators write themselves

Three examples from the operators' own pages, read on 2 September 2026:

Bitsler writes on its front page that all games run on verifiable technology. That is the operator's own claim, and it cannot apply to slot machines from other studios.
Rainbet states that its own games (Originals) build on such logic, while Case Battles and EOS Roulette draw their randomness from blocks on the EOS chain.
Wolfbet explains in its frequently asked questions that the server seed can be changed on the operator's side for checking, either per session or per bet ID.

Note the difference between having the arrangement and saying one has it. It is the panel with the hash and the seeds that makes the check possible for you. If you cannot find such a panel in the game you open, the arrangement does not apply to you there, whatever the front page says. Look for it in the settings or in the history before you put money into the game.

What provably fair proves

In short: that one particular round was not altered after it was locked. More precisely, a successful check shows that

the server seed you had revealed is the same one that lay behind the hash you saw beforehand,
the outcome follows from the three values by the method described,
the operator could not choose the server seed after seeing your client seed and your stake.

That is a valuable answer to the question «was this particular round tampered with?». Note also what happens if the operator should refuse to reveal a used server seed, or if the revealed seed gives a different hash from the one you noted. Then the check has done its job: you have a concrete discrepancy to point to, with screenshots and the round number, instead of just a feeling that something was wrong.

What provably fair does not cover

The check has clear limits, and it is easy to read too much into it:

The house edge. An entirely recalculable game can have a table that gives the house a large margin. How much is returned over time is a different calculation, explained on the page about RTP and the margin.
The payout. That a win is real in the game says nothing about when or whether it comes out of the account, or which caps and document requirements apply.
The account. ID checks, periods, bonus terms and closed accounts lie entirely outside the arrangement.
Slot machines and live tables from studios. These use their own random number generators or physical cards and wheels, and they normally cannot be recalculated by you.
The licence. A seed check is not a licence number and does not replace a query in the register.
The result over time. Even an entirely correct game can give long losing runs. The check says nothing about how a session will end.

This is why we rank operators by their terms and the register, not by whether they have a seed panel. The five points and the scores for twelve operators are in the overview with files.

How to use the check in practice

You do not need to check every round. A few simple habits give a lot:

Set your own client seed before you start a session.
Note the hash of the server seed, preferably with a screenshot.
Change the server seed after the session, and check that the revealed seed gives the same hash.
Recalculate a couple of rounds, particularly the ones that surprised you, with the method the game states.
Use an independent tool for SHA-256 and HMAC, or write a few lines of code yourself, rather than trusting the operator's own calculator blindly.

If something is wrong, you have documentation to point to. If everything is right, you know the rounds were locked, and you can concentrate on what really decides how the balance goes: the table, the stake and how many rounds you play. The basic rules for a dice game with a target value are in the explanation of dice.

Remember that gambling should be entertainment. Set limits for time and amount, and get in touch with Hjelpelinjen (hjelpelinjen.no) if play starts to control you. The age limit is 18.

Frequently asked questions

Can the operator cheat even if the round can be recalculated?

In the round itself it is very difficult as long as you check the hash and recalculate, because the server seed was locked before you played. But the arrangement only covers the outcome. The table can be unfavourable, and what happens to withdrawals, document requirements and your account is in the terms. It is also possible to claim the arrangement without giving you a panel with the hash and the seeds, and then you have nothing to check.

Why should I change the client seed?

When you choose the client seed yourself, the operator cannot have chosen a combination of server seed and client seed beforehand. The hash of the server seed is already shown, and your seed comes on top of it. That gives you extra assurance that the outcome was not tailored to you. The change does not affect the chance of winning or the table, only which concrete figures the rounds get.

Does seed checking apply to slot machines and live casino?

Normally not. Slot machines from studios use their own random number generators that are tested in other ways, and live tables use physical cards, balls and wheels. The arrangement exists first and foremost in house games such as dice, crash, mines, limbo and plinko. If a page says every game can be verified, you should read it as a claim and look for the seed panel in each individual game.

What do I need to recalculate a round myself?

You need the revealed server seed, the client seed, the nonce for the round and the description of the method the game uses. First you check that SHA-256 of the server seed gives the hash you saw before the round. Then you work out the figure with the method, for example HMAC-SHA256, and turn it into an outcome. If it matches the history, the round was locked.