Provably fair explained: how crypto casino games prove they are honest

The problem

Players of crypto casinos want cryptographic proof that a result was not altered after the bet was placed.

The scheme

1. The operator generates a server seed and publishes its hash.
2. The player supplies (or auto-generates) a client seed.
3. Each round uses HMAC-SHA256(serverSeed, clientSeed:nonce) to derive the outcome.
4. When the server seed rotates, the old one is revealed so every past round can be re-computed.

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