Quote from: Namworld on June 27, 2014, 09:06:00 PM

Basically, the issue is that many casinos provide a new server hash for each bet. (Which means AFTER the client seed is provided unless you change it before every bet, because otherwise they will know your seed from last bet).

This system of one server seed for each rolls allows each bet to be "verified" immediately after each bet, but it's bad because it is meaningless if the client seed isn't also changed afterward before the roll. Those system designs probably result from wanting to provide instant bet verification and poor understanding of what makes something provably fair. Verification is actually harder to do and more tedious, because it is only provably fair if the player changes seed before each roll. If you're labeled as provably fair, that's what you should be getting by default. Not something optional that isn't explained to you.

Here's a simplified explanation of cheating that could be done through such a system by a nefarious casino operator:

Quote

You know how x2 is either roll under 49.5 or over 50.5 for 1% house edge dice site? x99 payout is roll under 1 or roll over 99? The losing rolls are always in the middle of the 0-100 rolling range.

So since a new server seed is provided for each new bet, they could select their server seed assuming the client seed doesn't change and give numbers that tend toward the center of the range instead of being random. Here's what would happen.

1. Client changes the seed after each new server seed, before every bet. He doesn't know server seed, so seed he provides should give a random number. (Painfully tedious, few actually do it, but for those who do, provably fair.)
2. Client doesn't change his seed. All bets are rigged and he doesn't play with a 1% house edge. This would be impossible to be caught since the roll would still match the seeds.

- No, you wouldn't be able to cheat the casino, because the number would still be randomly over/under 50. It would just be closer to 50 than average. The number doesn't need to be on the opposite side such that you could counter it by switching over/under to abuse it. It just needs to be closer to 50 than random numbers would, creating more losses for players. No counter.
- No, you wouldn't be able to notice that the website, across all players, has a much higher house edge than 1% which is unlikely. It's easy to fill with fake "lucky" account to compensate for the actual players who are "unlucky" and have a credible total wager volume/profit. It's also easy to limit to large account/smart targeting.
- No, you wouldn't be able to notice that no actual players report winning, because even if they gave themselves a 2% or 3% house edge or targeted accounts doing large bets for a very large house edge, there would still be winners.

The point is, every player could verify all their bets, it wouldn't catch this kind of cheating.

Many dice games/casinos use such a flawed system. There should never be any scenario where server seed are generated after the client seed as it allows the casino to do selective seeding! If a player can play that way, the system is flawed, because it's possible to make a provably fair system where the player is always covered. Players don't need to choose between provably fair or spamming bets.

Just-Dice was a very good example of a correct implementation. You still had to change your client seed after receiving the server seed, but server seed stays the same, until you request it to be revealed to verify bets. At will verification, but you must not forget to then change your client seed. Get new server seed, THEN add your seed, then good to go to spam bets.

Coinroll is another good example, where a daily predisclosed secret is used for everyone. This make changing it after the fact very hard as it would impact all rolls for the day, plus the hash is provided upfront making it pretty much impossible to find another secret which matches the hash. Verification is delayed slightly but we believe this is the best method currently available. We also don't provide a default client seed. We use the client's last deposit tx, which means we don't even have the possibility to choose a default client secret that would be advantageous for the current daily secret. The only way Coinroll could cheat would be by providing rolls that don't match seeds. It makes it hard to cheat as this would be easily noticeable that some bets results are not right. Even if a casino did it for only 1% of players/bets, it would only need a few people tracking bets to start noticing. We also provide archives of all betting on Coinroll for public auditing.

A well designed provably fair system is supposed to make it possible and easy to spot fraud by the operator. A system where the player can either choose to be covered with tedious manual work (changing seed before each bet) OR bet at will without being able to check if bets are actually provably fair is not needed and pointless when players could be covered at all time with a system like Coinroll's or Just-Dice's.

Regards from Coinroll's staff

Please add your input to this thread to let casino operators know of your support for all crypto gambling venues to update their provably fair system and be bound to higher transparency standards. I would also recommend gambling list creators start demanding systems similar to Just-Dice's or Coinroll's for being listed as provably fair.

What would be the best approach to make a decentralized dice roll where users can be house if they want. And casino creating server seeds cannot cheat to win the pot itself by playing as a player?