What Is Provably Fair?
With traditional online casinos you have to entirely trust that the online casino is using a random number generator that is genuinely random and not rigged in their favour because they generate the results of the spins themselves.
Provably fair is a cryptographic system that allows players to verify that the outcome of any gambling bet was predetermined by the player and the casino itself.
The system was pioneered by Bitcoin gambling sites and since then has become one of the most significant innovations in the online gambling industry.
How It Works — Step by Step
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Casino generates a Server Seed. Before the online casino session the server seed is generated by the online casino and the hash of that seed is sent to the online casino client software. The casino cannot reveal the server seed itself as this would allow them to change the outcome of the spins afterwards.
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You provide a Client Seed. The player's seed is generated by the client software or it can be set to a custom value by the player. The player has complete control over this value.
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A nonce (spin counter) increments. Each individual spin of the online casino roulette wheel or slot uses a unique nonce which is a counter that increases by one with each spin.
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The outcome is calculated. The outcome of each spin is determined by a cryptographic hash function that incorporates the server seed, the client seed and the nonce.
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After the session, the server seed is revealed. After the casino session the server seed is revealed which allows the player to calculate the hash of the server seed themselves. The two hashes must match for the outcome to be provably fair.
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You verify any spin. With the server seed and the client seed and the nonce used during that session it is possible to calculate the outcome of each spin that occurred during that session. If that calculated outcome matches the one shown to the player during the session the result is provably fair.
Provably Fair vs Licensed RNG Slots
| Feature | Provably Fair | Licensed RNG |
|---|---|---|
| Verifiable by player | ✅ Yes | ❌ No (trust the auditor) |
| Third-party audited | Sometimes | ✅ Required for license |
| Game variety | Limited (crypto-native games) | ✅ Massive (Pragmatic, NetEnt, etc.) |
| Regulatory oversight | Varies | ✅ Strict (MGA, UKGC, etc.) |
| Jackpot availability | Limited | ✅ Wide range |
In the case of jackpot slots most major slot machine titles use licensed RNGs rather than provably fair software as the mechanics of jackpot slots require centralised coordination.
Casinos With Provably Fair Jackpot Games
Stake and Rollbit both offer their own proprietary forms of jackpot slots that are provably fair but there are very few, if any, fully provably fair jackpot slots available from third-party online casino developers. The majority of the available jackpot slot machines use certified random number generators.
One of the newer forms of incorporating randomness into the outcome of games on blockchain-based online casinos is to use on-chain randomness based on verifiable delay functions and oracles based on the blockchain.
How to Verify a Spin Yourself
Most provably fair casinos have a built-in verification tool in your account. But you can also verify manually:
- In order to manually verify the outcome of a spin during an online casino session the player uses the fairness settings of their online casino account to reveal the server seed.
- The player also notes their client seed and the nonce value for the specific spin that they wish to verify.
- These values can be entered into a HMAC-SHA256 calculator which will calculate the hash value and convert that hash value to the slot machine outcome to verify that the outcome matches that which was displayed to the player during that session.