Fair draws

We use a commit-and-reveal system. That means we lock in the randomness before anyone buys a ticket, publish proof of it, and reveal it afterwards so anyone can check we didn't change anything.

Main draws

1. Before launch we generate a random secret seed and publish its SHA-256 hash on the competition page.
2. At the draw we take every confirmed ticket number, sort them, join them with commas and hash the list (the entries hash).
3. The winning position is HMAC-SHA256(seed, entries hash) read as a number, modulo the number of tickets. The ticket at that position in the sorted list wins.
4. At closing time the full list of confirmed entries — paid and free — is frozen and its hash recorded. Nothing can be added, removed or changed after that, and the draw is made from exactly that list.
5. After the draw we reveal the seed. Check its hash matches the one published at launch, open the competition's entry list from Draw results, and recompute the winner yourself.

Redraws

If a winner can't receive the prize under our terms (for example, they fail age verification), a redraw picks a new winner from the same frozen list with every previous winning ticket removed. It uses the same seed, with the attempt number added so it can be checked: HMAC-SHA256(seed, hash_of_remaining_tickets + ":redraw:" + attempt), where attempt is 2 for the first redraw. The original result and the reason stay on the competition's page.

Instant wins

Instant-win numbers are chosen at random and sealed before a competition goes live. We publish a hash of every number and prize plus a secret salt. When the competition closes, we reveal the salt and any unclaimed numbers so you can confirm the list never changed.

Check a main draw yourself (Python)

import hashlib, hmac
seed = "REVEALED_SEED"
tickets = sorted([...])  # every ticket number from the entry list
print(hashlib.sha256(seed.encode()).hexdigest())  # matches the published hash
digest = hashlib.sha256(",".join(map(str, tickets)).encode()).hexdigest()
i = int(hmac.new(seed.encode(), digest.encode(), hashlib.sha256).hexdigest(), 16) % len(tickets)
print("winning ticket:", tickets[i])

Check instant wins

import hashlib
salt = "REVEALED_SALT"
prizes = [(17, "£10 Credit"), (342, "£50 Credit")]   # every number:prize, sorted by number
body = ",".join(f"{n}:{t}" for n, t in sorted(prizes))
print(hashlib.sha256(f"{salt}|{body}".encode()).hexdigest())  # matches the sealed hash