How Sorteo makes a lottery draw provably fair
A lottery is only as trustworthy as your ability to check it. When seats are scarce, “trust us, it was random” isn’t enough. Sorteo is built so anyone — a family, a board member, a journalist — can confirm a draw was fair without having to trust the district or Sorteo.
The problem with “trust us”
A draw run in a spreadsheet with a random-number generator can’t really be audited after the fact. Once it’s done, there’s no way for an outsider to tell whether an entry was quietly added or removed, or whether the random seed was re-rolled until the “right” families won. The result might be perfectly fair — but fairness you can’t check is just a promise.
Three ingredients make a draw checkable
Sorteo combines three things so the outcome speaks for itself:
- A public randomness beacon. The draw’s randomness comes from drand, a public beacon run by the League of Entropy that publishes a fresh, unpredictable value every few seconds. Nobody can predict or control it, and every value is signed and publicly archived. Sorteo pins a specific upcoming round before the draw — so the randomness is chosen but not yet known, leaving no way to grind for a favorable result.
- An input commitment. Before the draw, Sorteo publishes a hash — a fingerprint — of the exact entries and seat counts. Change a single entry and the fingerprint changes, so the commitment published ahead of time proves the inputs weren’t altered afterward.
- A tamper-evident transcript. The published record ties the commitment, the drand round and its value, the algorithm, and every seat assignment together. Re-running the same algorithm on the same inputs and the same beacon value reproduces the exact same result — every time.
How to check a draw yourself
On any lottery’s public results page you can see the input commitment and the drand round the draw used. The page checks that round’s value against the live drand beacon and shows a verification badge, and you can download the full transcript as JSON to re-verify it offline or hand it to someone else. Nothing depends on taking Sorteo’s word for it. See how the whole process works →
Why it matters
A draw you can prove is fair is defensible — to the families who didn’t get a seat, to a skeptical board, and to the public. It also protects the people running it: there’s no room for a quiet thumb on the scale, and no need to ask anyone to simply believe there wasn’t one.