Verifying Provably Fair Bets

Players with doubts about a casino’s honesty can check whether a crypto bet’s outcome matches the inputs promised before play. Verifying a provably fair game is a two-step process: matching a pre-committed hash to a revealed seed, then using those inputs to reproduce the recorded result.

What Gets Checked

Provably fair verifiers use four core inputs. The casino’s server seed is shown after the cycle, while the client seed is chosen by the player each time. The nonce is the third seed, added for each game to ensure “the game worked correctly.” The server seed hash, also called the commitment or pre-hashed value, is what players must save before any play. The verifier checks two things: that the revealed seed matches the pre-bet commitment, and that the reconstructed outcome matches the recorded history.

“If the hash of the server seed can never be known before the result of the bet is generated, then we can guarantee that the house simply could not have rigged the bet after knowing what the client side seed would be, because the server side seed would have already been secure.”

The Seed Timeline

The seed verification process follows this order:

1. The casino reveals a hashed server seed, also called a commitment or pre-hash. This must be saved to a local device.
2. Play begins, with the player choosing a client seed and the verifier getting the current nonce.
3. After the round, the full server seed is revealed, but usually not immediately. Some casinos like Boxed.gg delay the reveal for up to 24 hours before verification.
4. With the server seed revealed, the player can verify the outcome by putting the server seed, client seed, and nonce into a verifier.

Cloudbet’s provably fair page gives a complete walkthrough: “Note the commitment and Client Seed before you Make a Bet. Place your bet and take the result. Once you rotate seeds after the round, the server seed is revealed. After that, hash the revealed Server Seed with SHA3-256 and compare it to the saved commitment. Enter the Server Seed, Client Seed, and Nonce into the Bet Verifier to reconstruct the result from scratch.”

What Inputs the Verifier Needs

Any provably fair verifier needs four inputs:

• The revealed server seed, as a string of between 10-30 numbers or characters
• The chosen client seed, as a string, memo, or two to five integers
• The current nonce, a number or string that is incremented for each bet
• The game’s verification calculator or sandbox

Some provably fair verifiers implement HMAC-SHA256 with the input order: server seed first, then client seed, then nonce.