FairLock is the draw system behind every competition on Basecomp. It seals the draw before a single ticket is sold and reveals everything afterwards, so players can check a draw was fair for themselves instead of taking anyone's word for it.
Before the competition opens, every instant win is given a position at random and sealed away, so nobody knows which tickets will win them. Each ticket is checked as it is bought, without opening the seal, so a win shows up for the operator at the same moment it does for the player.
A random number is sealed before sales too. When the competition closes, it is combined with a second random number that drand, a public service run by independent organisations including Cloudflare, publishes only after the last ticket is sold. The result, divided by the number of valid tickets, picks the winner. The method is fixed in advance, but the winner can't be known until the competition closes, not even by us.
Most "verified draw" tools only cover the grand prize. On a modern competition most of the prize value is in instant wins, so FairLock covers those too.
Instant win positions and the grand prize number are generated at random and sealed. A fingerprint of them (a SHA-256 hash) is published.
Tickets sell. Instant wins are detected without opening the seal. Nothing sealed can change without the fingerprint changing too.
When the competition closes, the sealed number, a public random number published after the last ticket and the final ticket count pick the grand prize winner. The draw runs once and can't be re-run.
Everything sealed is published: every instant win position, claimed or not, the grand prize number and the public random number it was combined with. Anyone can recompute the fingerprint and check it matches.
Within a few hours of a competition being published, its fingerprint is recorded on the Bitcoin blockchain through OpenTimestamps. That gives it a date nobody can alter, so the claim that the draw was sealed long before it ran doesn't rest on Basecomp's own clock. Only the fingerprint is sent, never the sealed data.
Every competition published on Basecomp has a Verify page. After the draw it shows the sealed data, the sums, and the exact text behind the fingerprint, ready to download. Hash it with any SHA-256 tool and compare. The winner sum needs a big-number calculator, and the Verify page shows it worked through.
On a store's site, open any competition and choose Verify this competition, or click Verify draw next to any winner.
The full technical detail, with every formula, is in How FairLock Works: Inside a Verifiable Draw.
FairLock is on every competition you run on Basecomp, from the first one. Nothing to set up, nothing extra to pay.
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