Provably fair explained: what it proves and what it does not
How hash commitments and seeds let a player check a crash round after it ends, and why that shows the round was not altered rather than that the odds are good.
Some online games, crash games in particular, are described as provably fair. The phrase sounds like a guarantee, so it helps to be clear about what it covers. It lets a player check that a round was not changed after bets were placed. It says nothing about how good the odds are.
The sealed envelope idea
The method is called a commitment scheme. Before a round, the game picks a secret server seed and publishes only its hash. A hash function turns any input into a fixed-length fingerprint. Nobody can practically work backwards from the fingerprint to the seed, yet anyone can recompute it from the seed later. The published hash works like a sealed envelope: the game has committed to its seed before the round is played.
Many games also let the player supply a client seed, so the crash point depends on both seeds and the game cannot pick a seed to suit a particular player. The design varies by provider, and some games rely on a certified random number generator instead.
Checking a round after it ends
Once the round has crashed, the game reveals the server seed. A player can then:
- hash the revealed seed and confirm it matches the hash shown before the round;
- combine the seed with any client seed, using the method the game publishes;
- run the published formula and confirm it gives the crash point that was displayed.
A commonly described formula is floor(100 x (1 - edge) / (1 - X)) / 100, where X is a random number between 0 and 1 taken from the bits of the hash. The exact formula depends on the game.
What it does not prove
A matching hash proves the result was fixed in advance and not altered afterwards. It does not prove the odds are generous. The house edge is built into the formula. In the common model, the chance of reaching a multiplier m is (1 - edge) / m, and the edge is commonly 1% to 4% depending on the game. At a 1% edge the chance of reaching 2.00x is 49.50%; at a 4% edge it is 48.00%.
The same formula also produces rounds that end at 1.00x, where no cash-out is possible: about 1.98% of rounds at a 1% edge and about 4.95% at a 4% edge.
So provably fair describes the honesty of the process, not the value of the bet. A game can be fully verifiable and still return, on average, less than players stake. Read the stated house edge as well as the fairness page.
This guide is for information only and is for adults aged 18 or over, or the legal age where you live. If gambling stops being fun, take a break and consider contacting a local support service.
18+ only. This article is for information, not advice to gamble. Responsible gambling.
