Every crypto casino claims provably fair games. We reverse-engineered 60+ casino implementations into one open verifier — here's how the cryptography actually works, and the one step 90% of players skip.
"Provably fair" sounds like marketing until you rebuild the math yourself. We did — our verifier now covers 13 game types across 60+ casino implementations, from Stake's HMAC-SHA256 construction to EOS blockhash draws. Here is the mechanism in plain terms.
1. The commitment. Before you bet, the casino shows you a hash of its secret server seed. A hash is one-way: the casino cannot change the seed afterward without changing the hash you already saw.
2. Your input. You contribute a client seed (change it anytime) and each bet increments a nonce. The result is computed deterministically from all three values — typically HMAC_SHA256(server_seed, client_seed:nonce), mapped onto the game's outcome space.
3. The reveal. When you rotate your seed pair, the casino reveals the old server seed. Now you can recompute every past result yourself and check two things: the revealed seed hashes to the commitment you saw earlier, and every outcome matches what you were served.
Verification only works after you rotate your seeds. If you never change your client seed, the casino never reveals the server seed, and you're trusting, not verifying. Rotate after every session — it takes ten seconds and converts the entire history of your play from "trust us" into arithmetic.
Provably fair doesn't prove a casino will pay you — that's what licenses, payout speed data and on-chain wallet analytics are for. But for the narrower question "was this bet settled honestly?", it is the only complete answer gambling has ever had.