Provably Fair Social Casino: How Bink.bet's HMAC-SHA256 System Works
Most social casinos ask you to trust the server. Bink uses cryptographic commit/reveal so you don't have to.Every Bink Original derives its outcome from a one-way hash that's committed before any bet is placed — once committed, the server cannot change the seed without detection. After the seed rotates, you can independently re-derive every outcome you played.
Step 1 — Seed pair generation
At signup (or on rotation), Bink generates a 256-bit random server seed. The player picks or accepts a client seed. These two halves together drive every outcome until the player chooses to rotate.
Step 2 — Commit
Before you place a single bet, Bink publishes SHA-256(serverSeed) — a one-way hash of the server seed. You record this hash. The server now cannot change the seed without the hash changing, and the published hash is permanent.
Step 3 — Round derivation
For round n, the outcome is derived from:
HMAC-SHA256(serverSeed, clientSeed + ":" + n)The first 8 bytes of the HMAC output map to a 0.00–100.00 float, then through a game-specific outcome function (Dice maps to a roll; Plinko maps to a peg sequence; Roulette maps to a slot; and so on).
Step 4 — Reveal
When you rotate seeds (or on Bink's automatic rotation), the server seed is revealed. You verify SHA-256(revealedSeed) === committedHash. If it matches, the server never swapped the seed mid-session — every round you played was derived from the seed you committed to at the start.
Step 5 — Re-derive
With the revealed server seed, the client seed, and the nonce, you can independently re-derive every outcome of every round. Bink's on-site verifier accepts the triplet and returns the exact outcome the server produced. Mismatches would prove tampering — there have been none, and the algorithm is open source.
What's different about Bink
Stake.com pioneered provably-fair gaming in 2017. Bink ships the same cryptographic guarantees in a U.S.-legal sweepstakes social-casino model — something Chumba, LuckyLand, and Pulsz don't do. None of those competitors publish a live verifier or expose the seed-commit hash.
Source code is open at packages/crypto-utils/src/games/. The live verifier sits at /provably-fair and at /games/<game>/verify per game.
Try Bink free
Free Gold Coins + free Bink Cash on signup. No purchase necessary. 18+. Available in 39 U.S. states.

