Provably fair
Provably fair is a system that lets you check for yourself that a casino fixed its part of a bet's result before you bet and did not change it afterwards.
Also called provable fairness, provably fair gaming
In a provably fair game the casino picks a secret server seed and shows you its hash before you bet. The hash is a commitment: it locks the seed in without giving it away. Each result is then worked out from the server seed, your client seed and a nonce that counts your bets. When you change seeds, the casino reveals the old server seed.
Example. You saved the hash shown before you played. Later the casino reveals the seed. You run SHA-256 on the seed and get the same 64 characters as the saved hash. That shows the seed was fixed before your bets. The provably fair verifier runs this check in your browser.
What people get wrong. Provably fair does not mean a game is generous, and it does not remove the house edge. It only shows the result was not changed after you bet. It also covers only the games that use it, usually a casino's own dice, crash or mines games. Slots from outside studios usually use an ordinary RNG.
Note
A match only means something if you saw the hash before you bet. Save it or take a screenshot first.
Related terms
- Server seed
A server seed is a secret random value a casino picks before you bet and uses, together with your client seed and a nonce, to work out provably fair results.
- Client seed
A client seed is the player's input to a provably fair result, a value you can set yourself that is mixed with the casino's server seed and a nonce.
- Nonce
A nonce is a counter that goes up by one with each bet, so that every bet made with the same pair of seeds gets a different result.
- Hash
A hash is a fixed-length fingerprint of some data, where the same input always gives the same hash but the hash cannot be turned back into the input.
- Random number generator (RNG)
A random number generator (RNG) is the software that produces the unpredictable numbers a casino game turns into spins, cards and dice rolls.