How Provably Fair Works (and How to Check a Roll Yourself)
The maths behind provably fair games, in plain English, plus how to verify any Betrefs free case roll.
Updated
Provably fair means you don't have to trust the site. You can check every result yourself.
The three ingredients
- Server seed. A random secret the site generates. Before you play, you only see its SHA-256 hash, which locks it in.
- Client seed. A value you control. Change it whenever you like, so the site can't know the final input in advance.
- Nonce. A counter that goes up by one each time you play, so every roll is different.
How the roll is made
The site combines the three with HMAC-SHA256, takes the first 52 bits of the result and reduces them to a ticket between 0 and 999,999. Each prize owns a range of tickets, and the range your ticket lands in decides the prize.
Checking it
When the server seed rotates, the site reveals the original. Hash it: if it matches the hash you saw before playing, the seed wasn't changed. Then run the same calculation, or use our verifier, and you'll get the same ticket.