Provably fair is the most important innovation in online gambling transparency. It is a system where you can mathematically prove, for any given bet, that the casino did not know the outcome before you placed it and could not have changed it after. No traditional casino, physical or online, can make this claim.
The three components: server seed, client seed, nonce
Every provably fair game uses three inputs to generate a result. The server seed is a random string generated by the casino before the round starts. The client seed is a random string you contribute (you can change this yourself at any time). The nonce is a counter that increments with every bet you place, ensuring each round produces a unique result even with the same seeds.
These three inputs are combined using a cryptographic hash function (usually HMAC-SHA256) to produce the game result. The result is deterministic: the same inputs always produce the same output. This means you can verify independently that the inputs the casino claims to have used actually produce the result you received.
How the commitment prevents cheating
Before the round starts, the casino commits to a server seed by giving you its SHA-256 hash. A cryptographic hash is a one-way function: you cannot reverse it to find the original seed, but you can verify after the round that the seed the casino reveals actually matches the hash they gave you.
This is what prevents cheating. If the casino wanted to change the outcome after seeing your bet, they would need to use a different server seed. But their committed hash would no longer match, and you would catch the discrepancy when you verify. The system makes cheating detectable, not just impossible.
How to verify a result on Rollify
In your Rollify account, go to the provably fair section. Any completed bet shows the server seed (now revealed), client seed, and nonce used. Copy these three values into the verification calculator on the same page, and it will compute the result and confirm it matches your bet outcome.
You can also change your client seed at any time before a bet to ensure the casino cannot know what game results your future bets will produce. Most players never need to change it manually since the system is already secure, but the option is there.