Win a Car Clean

The method · VERITY-1

How the result is made

commitment   = SHA256(seed)                      published at launch
entries_hash = SHA256("VERITY-1|entries|{ref}\n" + "{ticket}|{owner}" lines, sorted by ticket)
draw_seed    = HMAC_SHA256(seed, "VERITY-1|draw|{ref}|{entries_hash}|{beacon}")

for winner p = 1..k, counter c = 0, 1, 2 …
  x = first 12 hex chars of HMAC_SHA256(draw_seed, "pick|{p}|{c}") as an integer
  if x < floor(2^48 / n) * n:  winner = entries[x mod n]; remove it; next p

instant wins: key = HMAC_SHA256(seed, "VERITY-1|instant|{ref}")
  slot s, attempt a: ticket = 1 + sample(key, "slot|{s}|{a}", max_tickets), skipping repeats
  table_hash = SHA256("VERITY-1|instant-table|{ref}\n" + "{ticket}|{prize}" lines)

Owners appear only as anonymous tags. Plates are partly hidden to protect winners’ privacy.