Provably Fair

The principle

Provably fair is a cryptographic system that lets the player verify game outcomes were not manipulated by the casino. The math runs in the player's browser using inputs that the casino cannot change after the fact.

How it works on Stake

Three values combine to produce every outcome:

1. Server seed: a 64-character hex string generated by the casino. The SHA-256 hash of this seed is shown to you before any bet, but the seed itself is hidden until later.
2. Client seed: a string under your control. You can set it to anything; default is randomised by the browser.
3. Nonce: an incrementing counter starting at 0, advancing 1 per bet within a server seed pair.

The bet outcome is computed by HMAC-SHA256-hashing the combination of these three inputs and parsing the resulting bytes into a probability distribution specific to the game.

Verifying yourself

After your session, request a new server seed pair on Stake. The previous server seed is then revealed. You can:

1. Verify SHA-256(revealed_server_seed) matches the hash that was shown before betting.
2. Re-compute every outcome by feeding (server_seed, your_client_seed, nonce) through HMAC-SHA256.
3. Confirm each computed outcome matches the actual outcome you saw.

If any step fails, the casino has manipulated the result. If all steps pass, the outcomes were demonstrably fair.

What provably fair does NOT do

It does not eliminate the house edge. A provably fair Plinko round still has a 1% house edge — verifiability is about process integrity, not winning. It does prove that any losses you experienced were due to the published distribution, not casino tampering.