Provably fair explained: what it proves and what it cannot
Provably fair is a mechanism to check if a casino alters the results of a bet after you make that bet. The casino locks the result before the bet and shows you a fingerprint of the result. Later the casino reveals the original result so that you can check if it matches the fingerprint shown by the casino.
It is a real protection, but a narrow one. It proves a result was not altered. It does not ensure a game pays back a fair share, and it does not protect most slot games.
By Owen Sheridan · Updated
Provably fair explained in one minute
Before you bet, the casino creates a secret value called a server seed, and shows you only its hash, a fingerprint that cannot be turned back into the seed.
Your browser adds a client seed, and a counter called a nonce goes up by one for every bet. The three values determine the result.
When you change seeds, the casino reveals the old server seed. If the hash of that server seed matches the fingerprint shown by the casino, then it is guaranteed the casino did not change the server seed during play.
Winna's page shows server seed, client seed, nonce, and a bet checking tool.
How provably fair works, step by step
The order is what makes it work. The casino commits to its part before it knows yours, and you add yours before you know the result.
A slot studio, BGaming, that integrates this system into its games, describes the same order with SHA-256 hashing on its provably fair page.
- 1. The casino commits
It creates a server seed and shows you its hash.
- 2. You add your part
Your client seed is set before the bet; the nonce counts the bets.
- 3. The result is calculated
Server seed, client seed and nonce are hashed.
- 4. The seed is revealed
After you rotate seeds, the old server seed is shown in full.
- 5. You check
Hash the revealed seed and recompute the result from the three inputs.
A provably fair hash, worked through
Hash functions are transformations that take any length of text and create fixed length values (also called fingerprints or hashes). The same piece of text always hashes to the same value. Changing just one character always results in a different hash.
The two lines next to this are real SHA-256 hashes of two example seeds that differ in their last character. You can check them with any SHA-256 hash tool.
Thus, a casino cannot change a seed after showing you its hash, because the new seed would not match.
- SHA-256 of rtpfinder-example-seed-1
- 83bcd36415236d44e8bd9480e4d577df52f30b839284877f94ae02a6fbee77a7
- SHA-256 of rtpfinder-example-seed-2
- 6fbe221ee11c3fecded3210f539c78e7fa7337703525c2b6dcc3950a331a9b22
Which games are provably fair
Provably fair needs the casino, or the studio, to run the seeds. This works best with simple in-house games: dice, crash, mines, plinko. Rakebit lists 15+ provably fair Originals of this type.
Slots from Hacksaw, Pragmatic Play and Quickspin load their games from the studio's server. Their information screens show an RTP and no seed to check. Their fairness relies on the studio's random number generator and outside testing.
Winna's page claims that every game on Winna is powered by provably fair technology. The seed check described on their page applies only to games running on their system; for third party slots, the rules screen is the place to check RTP.
Where that RTP is in each studio's rules: how to check slot RTP.
| In-house Originals | Studio slots | |
|---|---|---|
| Who runs the maths | The casino | The studio |
| Check a single result | Yes, with the seeds | Usually not |
| Where the RTP is stated | Game or casino page | The game's rules screen |
| RTP versions | Set by the casino | Chosen from the studio's list |
Provably fair is not the same as a good RTP
A provably fair game shows how each result was fixed in advance. Payouts still dictate how much it returns. A dice game that pays out a little less than the true odds has a built in house edge, provably fair or not.
Rakebit gives its Originals an RTP of up to 99%. A top-version slot pays around 96.3%, and a lowered one can be 92% or less. Those differences cost far more than any doubt about a single result. Casinos that run the top slot versions: best payout online casinos.
The same gap as the casino's share: house edge vs RTP.
Average kept on €1,000 of bets
- 99% · Rakebit's best Originals€10.00
- 96.34% · Le Bandit, top version€36.60
- 92.17% · Le Bandit, lowered€78.30
Averages over many bets. Provably fair or not, one session can end far above or below averages.
Provably fair vs a tested random number generator
Regulated markets take a different approach. Games use a random number generator that an outside lab tests, and a regulator sets the rules it must follow.
For example, the UK Gambling Commission's remote standards prohibit games that adjust to previous results.
Provably fair technology lets you verify one result, while a tested generator relies on the lab and regulator. Terms of use of Kings Game mention both: outcomes "may rely on random number generation (RNG) or provably fair technology".
Why a slot's results can still swing widely: theoretical vs actual RTP.
Adaptive behaviour (that is, a compensated game) is not permitted.
Provably fair explained: FAQ
What does provably fair mean?
The casino commits to a hidden server seed before you place your bet and reveals it later. You can then check that the result has not been altered after your bet.
How do I verify a provably fair bet?
Rotate the seeds so the old server seed is revealed. Check that the hash of that seed matches the hash that was shown previously. Then, recompute the result using the server seed, client seed and nonce. Winna offers a tool for this.
Are slots provably fair?
The majority of them are not. Slots by studios like Hacksaw and Pragmatic Play are run on the studio's servers; BGaming is a studio that builds provably fair into their games.
Does provably fair mean a game has a good RTP?
No, it doesn't. It proves results were not altered. Payouts still set the RTP. Rakebit's Originals have an RTP of up to 99%, while a lowered slot can have an RTP of 92%.
Can a provably fair casino still cheat?
Not on a result you verify. It can still set low payouts, or pick lower RTP versions for its slots.
Is provably fair better than a tested RNG?
They are very different. Provably fair lets you check each result. A tested RNG relies on outside labs and a regulator.