# Provably fair

> Seed commitment, the hash-to-float derivation, rotation and verification, and versioned mathematics.

Source: https://casinoapipro.com/docs/provably-fair
Every outcome is derived from a hash the player can recompute. We commit to a server seed before play by publishing its hash, and reveal the seed when it is rotated — so a player can check, after the fact, that we did not choose the outcome once we knew their bet.

## The scheme

- Server seed — secret, ours, revealed on rotation.
- Client seed — the player's, changeable at any time.
- Nonce — a counter, incremented once per round.

```js
const hash = sha256(\
```

That single float drives the round. What it selects — which tile is a mine, where the multiplier stops — is the game's own mathematics, versioned per release.

## The commitment

Before a round, the launcher can read the current commitment: the _hash_ of the server seed, never the seed.

`GET /v1/game/state` — auth: game-launcher

```json
{
  "fairness": {
    "server_seed_hash": "9c1185a5c5e9fc54612808977ee8f548b2258d31…",
    "client_seed": "player-chosen-or-generated",
    "nonce": 41
  }
}
```

## Rotating and verifying

`POST /v1/game/seed/rotate` — auth: game-launcher

Rotation reveals the old server seed and commits to a new one in the same response. With the revealed seed the player can recompute every round played under it.

```json
{
  "revealed": {
    "server_seed": "8f14e45fceea167a5a36dedd4bea2543…",
    "server_seed_hash": "9c1185a5c5e9fc54612808977ee8f548…",
    "rounds": 41
  },
  "next": { "server_seed_hash": "b6589fc6ab0dc82cf12099d1c2d40ab9…" }
}
```

> **What the player checks**
>
> That `sha256(revealed.server_seed)` equals the hash committed _before_ they played. If it matches, the seed could not have been chosen after seeing their bets.

## Setting a client seed

`POST /v1/game/seed/client` — auth: game-launcher

A player who supplies their own client seed removes any doubt about our influence over the input. Setting one rotates the nonce back to zero.

## Versioned mathematics

Every game release is versioned, and each round records the version it was played under. A change to a payout table is a new release, never an edit — so a round played last year can still be verified against the exact mathematics in force at the time.

| Name | Type | Meaning |
| --- | --- | --- |
| `game_version` | string | Recorded on the round. What a regulator asks for first. |
| `server_seed_hash` | string | The commitment in force when the round was played. |
| `nonce` | integer | This round’s position in the seed’s sequence. |

## Where the randomness comes from

Server seeds are drawn from the operating system's CSPRNG. Nothing in the engine calls a seeded or time-based generator, and the engine has no access to a player's balance or stake when it computes an outcome — the mathematics and the money are separate layers by design.