Provably fair, explained
How dond.win proves that no round of Deal or No Deal is rigged: a SHA-256 commitment published before you pick, your own client seed mixed into the shuffle, both seeds revealed at the end, and a verifier page that recomputes all 25 cases.
The problem provably fair solves
In a normal online game you have to trust that the operator shuffled honestly and did not move the big prize after you picked. Provably fair replaces that trust with arithmetic. The operator commits to the shuffle before you act, lets you influence the shuffle with your own input, and reveals everything afterwards so you can check.
What happens in a round
- Commitment. Before you pick a case, the server draws a secret server seed and publishes its SHA-256 hash. The hash is shown in the game as the commitment. The server cannot change the seed later without the hash changing.
- Your input. You have a client seed. By default it is random; you can type your own in the buy-in panel before a round starts. The server cannot predict it.
- The shuffle. The 25-prize ladder is shuffled with Fisher-Yates, using random bytes produced by HMAC-SHA256 with the server seed as key and your client seed as message. Neither side can choose the layout alone.
- The reveal. When the round ends, the server seed is revealed next to the commitment and your client seed.
- Verification. Hash the server seed and compare it to the commitment. Re-run the shuffle with both seeds and compare every case with what you saw. The verification page does both in your browser; nothing is sent anywhere.
The exact algorithm
- commitment = SHA-256(utf8(serverSeed)), hex-encoded.
- block[i] = HMAC-SHA256(key = serverSeed, msg = clientSeed + “:” + i), for i = 0, 1, 2 …
- Each block yields eight big-endian 32-bit integers; r = value / 2^32. When a block is used up, take the next one.
- Fisher-Yates over the fixed ladder: for i from 24 down to 1, j = floor(r × (i + 1)), swap ladder[i] and ladder[j]. Case k receives ladder[k].
Anyone can implement this in a few lines of any language and get the same layout.
What it does and does not prove
It proves the layout was fixed before you picked and was not chosen by the server alone. It proves every offer you saw was computed from the real board. It does not change the odds: the ladder and the fees are what they are, and they are public too. Fairness here means the game you are shown is the game being played.
Checking an old round
The seeds and commitment are shown on the round-over screen and in your history. Paste them into the verification page at any time.
Frequently asked questions
Is Deal or No Deal on dond.win rigged?
The layout of every round is committed with a SHA-256 hash before you pick a case, mixed with your own client seed, and revealed when the round ends. You can recompute all 25 cases yourself on the verification page. A rigged layout would fail that check.
What is a client seed and should I change it?
It is your contribution to the shuffle. The default is random and already prevents the server from choosing the layout. Setting your own makes the round reproducible with a value only you picked.
Can the server pick a seed that favours the house?
It cannot know the final layout when it commits, because your client seed is mixed in afterwards. It also cannot swap the seed later, because the hash would no longer match.
Do I need any software to verify a round?
No. The verification page runs SHA-256 and HMAC-SHA256 in your browser. You can also use any programming language that has those two functions.