Roulette Verifier (European)

How digital roulette wheels work

A land-based wheel depends on ball speed, rim friction, and a dealer’s wrist. Online provably fair casinos swap all of that for cryptography: the server’s committed seed, your own client seed, and a per-round nonce are combined into one random floating-point value. That value — not physics — picks the pocket.

The result is then placed on the European layout: 37 pockets numbered 0 through 36. Since the casino publishes its server seed hash before your bets go down, it cannot shift the outcome after seeing where your chips landed. The math is locked in ahead of time.

The math: Mapping seeds to wheel pockets

Three steps turn an opaque hash string into a pocket number. Here is the full pipeline:

1. Converting the hash to a float

The verifier feeds your server seed, client seed, and nonce through HMAC-SHA256. It takes the first 4 bytes of the output and reads them as a decimal fraction U between 0 and 1:

U = Hex_To_Decimal(First_8_Chars) / 4294967296

2. Mapping to the wheel

Multiply U by 37 — the pocket count on a European wheel — and floor it:

Winning_Number = Floor(U * 37)

Every number from 0 to 36 lands with identical probability: 1/37 each. No pocket is weighted, no sector runs hot.

3. Deriving color, parity, and layout attributes

With the pocket fixed, standard table attributes follow mechanically:

• Zero: Green, neither even nor odd.
• Red/Black Map: Numbers [1-10] and [19-28] are odd-red, even-black. Numbers [11-18] and [29-36] are odd-black, even-red.
• Dozen: 1st Dozen (1-12), 2nd Dozen (13-24), or 3rd Dozen (25-36).

Data Sandwich: Auditing a Red 32 spin

Worked example. You staked $50 on Red and the ball landed on 32 — a winner. Seeds rotated, you paste three values into the verifier:

• Server Seed: 3e42ab...
• Client Seed: roulette_spin_seed
• Nonce: 8

HMAC-SHA256 produces a hash whose first 4 bytes convert to U = 0.874291. Now apply step two:

Winning_Number = Floor(0.874291 * 37) = Floor(32.348) = 32

Pocket 32 checks out as **Red**, **Even**, **3rd Dozen**. Identical to what your game history recorded. The round stands verified.

Frequently asked questions