How to prove a prize draw was not rigged

There are two situations where you need to prove a draw. The first: someone disputes it and you must answer. The second, more comfortable: you want to be able to answer before anyone disputes it. This page covers both, and starts with the bad news.

What proves nothing, despite appearances

The screenshot

It shows a result. It does not show the previous attempts, nor the list of entrants at the moment of the draw. A screenshot can be retaken as often as needed, and nothing distinguishes the fifteenth from the first.

The video, even live

A live stream beats an edited video, and remains weak. It establishes that a draw happened once in front of witnesses. It does not establish that the list of entrants was untouched beforehand: one name added, one removed, and the stream honestly films a biased draw.

The commitment made afterwards

Publishing the details of the computation after announcing the winner proves nothing either: nothing stops you from picking the winner first and manufacturing the computation that leads there. The order is the whole subject.

The notarised report: what it brings, what it does not

This is the classic answer, and it has one quality we do not have: a report drawn up by a bailiff or notary carries reinforced evidentiary weight before a court. If your need is to hold up before a judge in a declared dispute, that is the route, and we do not claim to replace it.

What it does not do, however:

• it attests on your behalf, and your audience must believe the attestation — the doubt is displaced, not lifted;
• it is expensive and booked in advance, which restricts it to operations of a certain size;
• it records how an operation unfolded, without letting an entrant redo the computation themselves.

In other words, the notarised report and the recomputable proof answer different questions. One answers “what can I show a judge”. The other answers “what can I show ten thousand people in the comments, right now, without asking them to trust me”.

What a verifiable proof actually contains

A DrawSeal draw publishes a commitment before and its reveal after. Concretely, here is what is laid down, and when.

Before: the commitment, at least 24 hours ahead of the draw

• a seal on our secret number: its value stays hidden, but we can no longer change it without it showing;
• the number of a future public randomness beat, produced at a fixed time by drand, an external source we do not control — it does not exist yet when we announce it.

At entry close: the seal of the list

• a seal on the list of entrants, which freezes it: a name added or removed afterwards no longer matches the seal, and that shows;
• the exact number of entrants kept after the anti-fraud rules were applied;
• the moment of sealing, and the number of the public randomness beat matching it.

After the draw: the reveal

The secret number is published. The computation becomes replayable by anyone: same inputs, same winner. Had we changed anything, the computation would not land on the announced name — and that would show immediately.

The certificate’s six checks

Every draw yields a PDF certificate carrying the result of six independent checks. These are not claims of ours: they are the six answers of the computation, and the public page recomputes them in the visitor’s browser.

• the revealed number is the one that had been sealed before the draw;
• the list of entrants is the one that had been sealed at entry close;
• the sealing happened before the draw, not the other way round;
• the public randomness used is the one announced, and it is authentic;
• the winners are the ones the computation designates;
• any reassignments follow the same computation, with no manual override.

The certificate carries a scannable code leading to the draw’s public page. That is what makes it useful: the document alone does not ask to be believed, it points to what allows checking it.

Two outside witnesses, for the date

One objection remains: what if you published the commitment later than you claim? Two mechanisms answer it, both beyond our reach:

• a readable mirror on a third-party public forge, where the record is deposited as-is — anyone can consult it without going through us;
• a proof of date filed through OpenTimestamps on a public register nobody can rewrite, ourselves included. It attests that the document existed on that day.

And the code behind all of it

The draw engine is published under an open licence, on GitHub and on npm, and it is the engine — the one the service runs, not a demo copy. The verification you run and the one we run are literally the same code.

The shortest way to judge for yourself: verify an existing draw. No account, nothing to install.

Read next

• Prize wheel alternative — why a wheel shows well and proves nothing
• Giveaway rules — what written rules must contain, clause by clause
• About us — who publishes the service, and what it refuses to do

Frequently asked questions