Want to know about Provably fair...

[BitCoinDream]

I see some gambling sites mention that they are provably fair. They provide some seed and ask to check some hash or whatever. My question is, can this fairness really be checked from outside ? Where are they twisting to make sure the house's win ?

[arieq]

Yes, one way to verify a game’s fairness is through the combination of a server seed and a client seed. We can compare the hash with the server seed that has been revealed by the house. If we find a match, then we can say that the game has a provable fairness.

So, basically a fair game result is calculated as follows:
1. The server creates a hashed server seed and sent to the player.
2. The player creates his own random client seed
3. The combination of the two seeds are used to calculate the result of the game.
4. The server seed is revealed to the player so the player can check wether it matches the hash that was sent earlier

[Wusolini]

I see some gambling sites mention that they are provably fair. They provide some seed and ask to check some hash or whatever. My question is, can this fairness really be checked from outside ? Where are they twisting to make sure the house's win ?

Yes, it can.


I can explain it on simple example, (just the principle)

BTCRock - it's game where you have a grid 20x20 and you have 6 attempts to find gold vein.


Their proof is that immediately after solving captcha you can see hash of "gold vein coordinates ".





After you made your 6 tries, a result is shown to you:


 



Proof is that from begining the coordinates  gold vein was [11,9], and was not moved if you luckily hit it ( it would change the hash)

You can check it using: http://www.xorbin.com/tools/sha256-hash-calculator

1 - enter: 65879c50984f5b9ede009960e6efa3c6|[11,9]    (proof of location, shown after game end)
2 - hash it (using sha2586)
3 - you'll get: c0344a8d187371c671d9e16cb27190a74caef8fe32ab66be7287ed050fca2b12       (this is what you know from begining)

tip: for clarity try to change one coordinate and hash it again, will see you got completely different hash.


P.S. This's only principle, and can be used in various way. You should check description on particular site.

[rarkenin]

These sites tend to use slightly counterintuitive terminology. Provably random? Yes. They can't pick results in advance; nor can you. Provably fair? No. They still get a bit of an edge to keep a profit, although they can be verified to not be taking more than their official rules say.

[williamj2543]

With a bit of php knowledge you can easily make your own 5 line script checking any websites fairness.
Look at my code for generating random numbers (pretty similar to other websites)

Code:

$hash = hash_hmac('sha512','TXID:BETS', 'SECRETKEY'); 
$firstfive = hexdec(substr($hash, 0, 5)); 
if($firstfive > 1000000) { 
$firstfive = hexdec(substr($hash, 6,5)); 
}
echo $firstfive/10000;

I take the TXID of the bet, the amount of bets, and then the daily secret key which the hash of the secret key is stored for people to check the next day. If the hash of the secret key matches the one shown on the list, that means the secret key was indeed used. These pieces of data are hashed together in sha512 using hmac. I take the first 5 digits of that hash and convert it from hexadecimal to decimal. This gives a number that 98% of the time is under 1000000 (if it isnt I take the next 5 digits), and then divide that number by 10000 and I get a two digit number out of a hundred with some decimal places. The next day the user can verify their bet by pasting in their TXID, their amount of bets, and then the secret key that is released the next day, and then run it through the script. If the echod number matches the number that was used on the gambling site, I was indeed telling the truth and their bet was fairly made. Every website explains their own method of fair betting.

[Rum152]

These sites tend to use slightly counterintuitive terminology. Provably random? Yes. They can't pick results in advance; nor can you. Provably fair? No. They still get a bit of an edge to keep a profit, although they can be verified to not be taking more than their official rules say.

I would say that they are fair in regard to the fact that they disclose the odds of winning ahead of time, and the actual odds are what they say they are.

[degold]

I see some gambling sites mention that they are provably fair. They provide some seed and ask to check some hash or whatever. My question is, can this fairness really be checked from outside ? Where are they twisting to make sure the house's win ?

Yes, it can.


I can explain it on simple example, (just the principle)

BTCRock - it's game where you have a grid 20x20 and you have 6 attempts to find gold vein.


Their proof is that immediately after solving captcha you can see hash of "gold vein coordinates ".





After you made your 6 tries, a result is shown to you:


 



Proof is that from begining the coordinates  gold vein was [11,9], and was not moved if you luckily hit it ( it would change the hash)

You can check it using: http://www.xorbin.com/tools/sha256-hash-calculator

1 - enter: 65879c50984f5b9ede009960e6efa3c6|[11,9]    (proof of location, shown after game end)
2 - hash it (using sha2586)
3 - you'll get: c0344a8d187371c671d9e16cb27190a74caef8fe32ab66be7287ed050fca2b12       (this is what you know from begining)

tip: for clarity try to change one coordinate and hash it again, will see you got completely different hash.


P.S. This's only principle, and can be used in various way. You should check description on particular site.

Thanks wusolini, you explained very well, I also always thought how probably fair work.

[mrhelpful]

I thought a seed can be manipulated..

[rarkenin]

I thought a seed can be manipulated..

Yes, but each side keeps a secret from the other side, so in the end all you can do is change the outcome without knowing what you change it to.

[mnmShadyBTC]

I thought a seed can be manipulated..

not when half of the seed is secret and bit revealed until the next day

[aatrox]

cant the casino just go back to learn your betting style?

[tinof]

The odd of winning is already on house side. Pointless to cheat and risk damaging the reputation.

[BitCoinDream]

I see some gambling sites mention that they are provably fair. They provide some seed and ask to check some hash or whatever. My question is, can this fairness really be checked from outside ? Where are they twisting to make sure the house's win ?

Yes, it can.


I can explain it on simple example, (just the principle)

BTCRock - it's game where you have a grid 20x20 and you have 6 attempts to find gold vein.


Their proof is that immediately after solving captcha you can see hash of "gold vein coordinates ".





After you made your 6 tries, a result is shown to you:


 



Proof is that from begining the coordinates  gold vein was [11,9], and was not moved if you luckily hit it ( it would change the hash)

You can check it using: http://www.xorbin.com/tools/sha256-hash-calculator

1 - enter: 65879c50984f5b9ede009960e6efa3c6|[11,9]    (proof of location, shown after game end)
2 - hash it (using sha2586)
3 - you'll get: c0344a8d187371c671d9e16cb27190a74caef8fe32ab66be7287ed050fca2b12       (this is what you know from begining)

tip: for clarity try to change one coordinate and hash it again, will see you got completely different hash.


P.S. This's only principle, and can be used in various way. You should check description on particular site.

That is an awesome explanation. I wonder how the house make sure that they win in the long term ? Do they really gamble with the user choice ?

[rarkenin]

I see some gambling sites mention that they are provably fair. They provide some seed and ask to check some hash or whatever. My question is, can this fairness really be checked from outside ? Where are they twisting to make sure the house's win ?

Yes, it can.


I can explain it on simple example, (just the principle)

BTCRock - it's game where you have a grid 20x20 and you have 6 attempts to find gold vein.


Their proof is that immediately after solving captcha you can see hash of "gold vein coordinates ".





After you made your 6 tries, a result is shown to you:


 



Proof is that from begining the coordinates  gold vein was [11,9], and was not moved if you luckily hit it ( it would change the hash)

You can check it using: http://www.xorbin.com/tools/sha256-hash-calculator

1 - enter: 65879c50984f5b9ede009960e6efa3c6|[11,9]    (proof of location, shown after game end)
2 - hash it (using sha2586)
3 - you'll get: c0344a8d187371c671d9e16cb27190a74caef8fe32ab66be7287ed050fca2b12       (this is what you know from begining)

tip: for clarity try to change one coordinate and hash it again, will see you got completely different hash.


P.S. This's only principle, and can be used in various way. You should check description on particular site.

That is an awesome explanation. I wonder how the house make sure that they win in the long term ? Do they really gamble with the user choice ?

They design the game so that in a fair, unmodified implementation under the rules, they get a house edge. A basic example would be a game that pays 2x a bet with provably fair "rolling", but you win 48% of the time. For instance, it picks a number between 1 and 100, and you win if it is less than or equal to 48.

[notlist3d]

Keep in mind even "fair" house comes out ahead.  The place you gamble at always will win over 50 percent overtime, if not it will go out of business.  You are betting on being one of the "lucky" ones.

[wunkbone]

Gambling sucks, you will lose in the long run due to house edge.

[Testing123]

cant the casino just go back to learn your betting style?

If you change the client seed randomly from to time, the house can't get advantage (other than the house edge) even if it knows your betting style.

[InwardContour]

Gambling sucks, you will lose in the long run due to house edge.

Yes, even if you play in provably fair websites.
There are many betting methods to try, but no one can ensure a long term win.
You are playing against the site owners, not against other players, therefore you are fated to lose.

[Malin Keshar]

There are possible issues with that probably fair stuff, see this topic

https://bitcointalk.org/index.php?topic=283547.0

And this article


for more info(article cited in the topic):

http://www.reddit.com/r/Bitcoin/comments/1frm4x/provably_fair_by_bitzino_not_provable_with/


There are also topics questioning if some sites are provably fair or not, you might want to search that subforum and see by yourself.

[ahri]

There are possible issues with that probably fair stuff, see this topic

https://bitcointalk.org/index.php?topic=283547.0

And this article


for more info(article cited in the topic):

http://www.reddit.com/r/Bitcoin/comments/1frm4x/provably_fair_by_bitzino_not_provable_with/


There are also topics questioning if some sites are provably fair or not, you might want to search that subforum and see by yourself.

Damn just went to the other thread.

Thanks for exposing that. Provably fair can be exploited..