Provably fair: which casinos let you verify your bets yourself? Step-by-step with Shuffle

[hazelbanjo]

A lot of casinos have "provably fair" written somewhere on their site, but actually checking a bet isnt always that straightforward. Sometimes you need an external tool, sometimes its not even clear what you're supposed to do with the seeds.

Hashing is part of my day job, so I got curious about how different casinos handle this. Shuffle seemed like a decent example since they actually explain the process and publish the code behind it.

Basically, before you place a bet, the casino shows you a hashed version of its server seed. The real seed stays hidden until you change it. Your client seed and a nonce are also used to generate the result.

For Shuffle's seed-based Originals games, the calculation uses HMAC-SHA256. The server seed is the key, while the client seed, nonce and round number make up the message. The generated bytes are then converted into a game result.

Sounds complicated but checking a bet on Shuffle is actually pretty simple:

1. Finish any games you still have open. You cant rotate seeds with an unfinished Mines game for example.

2. Open your bet history and find a completed Originals bet. Check its fairness details and note the client seed, nonce and hashed server seed.

3. Click Rotate Pair and choose a new client seed. This retires the previous server seed.

4. Go back to that same bet. The old server seed should now be visible.

5. You can use Shuffle's Verify button or their verification page to check the result. If you want to do it independently, they also publish the implementation so you can run the calculation yourself.

One important thing is keeping a record of the original server seed hash. That way you can compare it with the revealed seed later, instead of just trusting what the casino shows you afterwards.

There's a couple of limitations worth knowing too.

You can only verify bets made with a seed pair thats already been retired. Also, not every game uses exactly the same calculation, so the game-specific formula matters.

And this only covers Shuffle Originals. Slots from third-party providers use their own RNG systems, so you cant verify those bets the same way.

Provably fair doesnt mean better RTP or that a casino will always pay withdrawals without problems. It just gives you a way to check whether a game result matches the committed data.

Would be interesting to hear which other crypto casinos people have actually verified bets on. Especially if anyone's ever had a result that didnt match what the verifier showed.