Verify this draw

How this draw is provable

Before entries closed we published a commitment: a one-way fingerprint (SHA-256) of a secret random seed. After the draw we revealed the seed. Because the commitment was public before entries closed, the seed could not have been changed afterwards to pick a particular winner.

Commitment (published before entries closed)

440b22a7d035f2becfabf17721ee9be9388f7056cfb78f6743c757804a29ed18

Revealed seed (published after the draw)

14979e92f42b25a4eadf2e115a2ddc902642805e4959d8b6cfedddbbea3e1a35

Check it yourself

1. The seed matches the commitment

Run SHA-256 on the revealed seed - it equals the commitment above. For example, in a terminal:

printf '%s' '14979e92f42b25a4eadf2e115a2ddc902642805e4959d8b6cfedddbbea3e1a35' | sha256sum

2. The winning position comes from that seed

The position was derived from the locked-in seed and the final number of entries, so it couldn't be steered once entries were seen. Entries are counted in a fixed order (oldest first); this is a place in that list, not a ticket number. Recompute it and you'll get position 158:

$seed  = '14979e92f42b25a4eadf2e115a2ddc902642805e4959d8b6cfedddbbea3e1a35';
$total = 160;
$msg   = 'draw:019f1e20-0011-708a-81d0-6da87e270291:'.$total;
$span  = 1 << 60;                          // 60-bit space
$limit = intdiv($span, $total) * $total;   // reject above this to remove bias
$i = 0;
do {
    $n = (int) hexdec(substr(hash_hmac('sha256', $msg.':'.$i, $seed), 0, 15));
    $i++;
} while ($n >= $limit);
echo ($n % $total) + 1;                     // => 158

3. That entry holds the winning ticket #9

The 158th entry in that fixed order (oldest first) is the winner, and it holds ticket #9. To protect entrants' privacy we don't publish the full list of who entered, but we publish a fingerprint of it - so the order can't be altered after the fact - and we hold the full ordered list in our tamper-evident audit trail, available to the Advertising Standards Authority on request.

Entry-list fingerprint

026b79579b1443cd6ab637f5609f0016c45a7498da114f8ca0329be1252f6e0f