Useful, and narrower than advertised
Provably fair
It proves a specific result was not tampered with after you bet. It says nothing about whether the operator is solvent or will pay you.
How it works
Three inputs produce every result.
- Server seed. Generated by the casino and hashed before you play. You see the hash, not the seed. The hash is a commitment: the casino cannot change the seed afterwards without the hash no longer matching.
- Client seed. Set by you, and changeable. Your contribution to the outcome, which is what prevents the casino from precomputing results.
- Nonce. A counter incrementing with each bet, so the same pair of seeds produces a different result every round.
The three are combined with HMAC SHA256 and mapped to a game outcome. When you rotate your seed, the casino reveals the old server seed and you can verify that every result it produced was generated from the seed it committed to.
How to actually verify
- Set your own client seed before playing rather than accepting the default.
- Note the hashed server seed shown in the fairness panel.
- Play, then rotate to a new server seed. The old one is revealed.
- Hash the revealed seed and confirm it matches the hash you were shown.
- Run seed, client seed and nonce through a verifier to reproduce your results.
Because almost every operator we track uses the same HMAC SHA256 implementation, a verifier built for one generally works for the others. Gamdom hosts its verifier externally, which is better practice than keeping it in house, since a verifier controlled by the party being verified is a weaker guarantee.
The stronger variant
Duel uses the decentralised drand beacon operated by the League of Entropy as the randomness source for Crash. The outcome is derived from a public randomness beacon outside the operator's control entirely, rather than from a seed the operator generated.
That is a genuinely stronger guarantee than standard provably fair, because it removes the operator from the randomness generation rather than merely committing them to it in advance. Very few operators do this.
What it does not prove
Provably fair verifies that a specific result was generated from committed inputs. It does not establish any of the following:
- That the operator is solvent
- That your withdrawal will be paid
- That the published RTP is what the game actually runs at
- That the payout table is fair, only that the result was not tampered with
- That the operator will still exist next year
An operator can run perfectly verifiable games and still be a poor counterparty. The cryptography and the question of whether you get paid are unrelated, and only one of them is settled by a hash.
The honest summary
Provably fair is a real cryptographic guarantee about a narrow question, and it is meaningfully better than trusting an unverifiable RNG. It is also routinely presented as a general trust signal, which it is not.
Verify your results if you want to. Then judge the operator on operating history, scale and licensing, because those are the things that determine whether you get paid.
Gambling carries a negative expected return. Over enough bets the house edge wins by design, and no ranking on this site changes that. If it has stopped being a choice, free confidential help exists: Peluuri in Finland, Stödlinjen in Sweden, BZgA in Germany, and GamCare internationally.
Related
How we assess operators
Why standing is separate from anything the games can prove.
Originals RTP
The maths provably fair does not verify.