Provable Fairness

For developers and curious players: here is precisely how a deck is derived. The server and the in-browser verifier run byte-for-byte identical code, so you can reproduce any deal yourself.

1. The only source of randomness

Each hand begins with 256 fresh bits from the operating system's cryptographic RNG. This is the only randomness in the system — everything after it is deterministic, which is exactly what makes a hand reproducible.

serverSeed = randomBytes(32)   // 256-bit OS CSPRNG, one per hand

2. Commit → chain → shuffle → reveal

seedHash = SHA-256(serverSeed)                     // committed + ed25519-signed on-chain BEFORE bets
deckSeed = SHA-256(serverSeed | prevRevealedSeed)  // chains in the previous hand
deck     = FisherYates(52, HMAC-SHA256(deckSeed, counter))
// after the hand: reveal serverSeed → anyone checks SHA-256(serverSeed) == seedHash

Mixing in prevRevealedSeed — the previous hand's revealed seed, or genesis for a table's first hand — chains every deck to the one before it, so hands can't be secretly reordered or replayed.

3. The shuffle

• Random stream: HMAC-SHA256, keyed by the seed, over an incrementing counter (0, 1, 2, …) yields an endless stream of bytes, read 4 at a time as a 32-bit number. It's a standard, well-studied way to stretch one seed into unlimited unpredictable output (the HMAC-DRBG family).
• No bias: to pick a card position in [0, n) we use rejection sampling — discarding the small numeric tail that would otherwise slightly favour low positions — so every one of the 52! possible orderings is exactly equally likely.
• Fisher–Yates: the classic unbiased shuffle — walk the deck from the last card to the first, swapping each with a uniformly-chosen earlier card.

4. How the deck becomes cards

Cards are dealt from the end of the shuffled deck, with no burn cards:

• Hole cards: two per seat, in dealer order starting at the small blind.
• Community cards: the flop (3), turn (1), and river (1), in that order.