Provably Fair Explained: How to Verify a Crypto Casino Game Was Not Rigged

"Provably fair" is a cryptographic commitment scheme. Before you bet, the casino commits to a secret (the server seed) by showing you its hash. You contribute your own randomness (the client seed). Each bet uses a counter (the nonce). The result of every bet is a deterministic function of those three values, so once the server seed is revealed, you can recompute every outcome and confirm the casino could not have changed anything after seeing your bet.

The ingredients

• Server seed — a long random string generated by the casino. Secret during play; its SHA-256 hash is shown to you up front.
• Client seed — a string you can set or randomise. Because the casino does not know it when it generates the server seed, it cannot pre-select results.
• Nonce — increments by one each bet, so the same seeds produce a different result every time.

From seeds to a result

Most Originals use: HMAC-SHA512(server seed, client seed + ":" + nonce) → take the first bytes of the output → convert to a number in [0, 1) → map to the game.

• Dice: number × 100 → 0.00–99.99.
• Plinko: each row's left/right from successive bytes (byte < 128 → left).
• Crash: a hash chain where each game's hash is the hash of the next; the multiplier is derived from the hash with a 1% instant-crash rule.
• Mines: a Fisher-Yates shuffle of the grid seeded by the bytes.
• Roulette / Wheel: number × pockets → index.

How to verify (five minutes)

1. Before playing, note the hashed server seed shown in the fairness panel.
2. Set your client seed to something of your own.
3. Play a few rounds. Note the nonce for each.
4. Rotate the seed pair in the fairness panel. The casino reveals the old server seed.
5. Check SHA-256(revealed seed) = the hash you noted in step 1. If it matches, the commitment held.
6. Paste server seed, client seed and nonce into the casino's verifier (or an open-source one) and confirm each result matches what you saw.

Stake, Rainbet, Shuffle, Gamdom, BC.Game, Duel and Thrill all publish verifiers and the algorithm for each Original. Roobet publishes Crash and Towers verification. Coins.Game publishes verifiers for its Originals.

What provably fair guarantees — and what it does not

It guarantees that results were determined before your bet and could not be altered afterward. It does not guarantee the game has a good RTP: a provably fair Plinko with a 10% edge is still provably fair. Check the published house edge separately (1% at the brands above). It also does not cover third-party slots and live dealer games, which are certified by labs (GLI, iTech, BMM) rather than verifiable by you.

Why this matters for bonus hunters

Verification removes one worry from bonus play: that a casino might "tighten" results while you are clearing wagering. With seeds committed in advance, it cannot. Combine a verified Original with a rakeback code and you know precisely what you are paying for every bet — see our rakeback guide.

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