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[Announcement]BitShares PLAY Non-technical Whitepaper

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klosure:
Will the "quiz game" facility allow to implement sport bets?
To avoid a massive overhead on delegates, you should rely on oracle scripts stored on the block chain that would check the results of sport events on multiple bookmaker sites, reconciliate the results to detect inconsistencies, and input the resulst in the blockchain as signed messages. The role of delegates would then be to audi the oracles code, make sure they are reliable, and run them. Codius could be a good plateform for that.

pc:

--- Quote ---The solution is as follows, the ticket result will be drawn by 2 delegates:
The first delegate's random number is only in charge of producing a number X between 1 and 3 that determines that the Xth block after him will draw the random number for the ticket. The 2th delegate could be the evil guy who is trying to attack, but he can not predict who will produce the right drawing block before 4 blocks, his attack cost is (3 * BLOCK_TICKET_SALE), but his expected return is still only 1 block_ticket_sale. The only thing game rule need is to set the draw interval 1 block before the first delegate.

--- End quote ---

I think the reasoning here is wrong. The question is what can an evil delegate gain by withholding his random secret? The answer is: he gains another chance for winning with his ticket. And using this, he can rip off the network if this second chance gives him an overall expected return that is higher than the house edge.

Suppose for example a dice-like game with 50% chance of winning and 1% house edge. I. e. if you buy a ticket for 50 shares, 50% of the time you'll lose 50 shares and 50% of the time you'll receive 99 shares in return.

The evil delegate attacker buys one ticket in every block. This costs him 5050 shares per round. In 100 of these 101 cases he cannot influence the outcome, but he will win 50 of these 100 on average, for a total return of 4950 shares. For the last ticket, he either wins normally or gets a second chance, for a winning probability of 75% and an expected return of 74.25 shares. Obviously, 4950 + 74.25 < 5050, so in this setup the evil delegate loses in the long run.
If the evil attacker owns 2 delegates or if 2 delegates collude, they cannot influence 99 of their 101 tickets. For these 99 they receive 4900.5 on average and get a second chance for the remaining two (in some cases they will even get a third chance for one of the two), i. e. 2*75%*99 shares = 148.5. 4900.5 + 148.5 < 5050, so they are still losing.

But three colluding delegates can rip off the network: they have 98 normal winning tickets yielding 4851 in returns, and 3 second chance tickets (some of the time even a third chance, and in rare cases 4 chances) for an expected return of 3*75%*99 shares = 222.75. 4851 + 222.75 = 5073.75 > 5050.

logxing:

--- Quote from: pc on December 16, 2014, 09:49:58 am ---IIRC the proposed random number generation scheme had the problem that an individual delegate can decide to skip a block instead of producing a random number that would make him lose a game. (See https://bitsharestalk.org/index.php?topic=9489.msg139680#msg139680 ). Has that been addressed?

--- End quote ---

You can find infomation about this problem at
http://www.bitsuperlab.com/pdf/BitSharesPlayWhitePaper.pdf


--- Quote ---The solution is as follows, the ticket result will be drawn by 2 delegates:
The first delegate's random number is only in charge of producing a number X between 1 and 3 that determines that the Xth block after him will draw the random number for the ticket. The 2th delegate could be the evil guy who is trying to attack, but he can not predict who will produce the right drawing block before 4 blocks, his attack cost is (3 * BLOCK_TICKET_SALE), but his expected return is still only 1 block_ticket_sale. The only thing game rule need is to set the draw interval 1 block before the first delegate.

--- End quote ---

cass:
thx for sharing

pc:
IIRC the proposed random number generation scheme had the problem that an individual delegate can decide to skip a block instead of producing a random number that would make him lose a game. (See https://bitsharestalk.org/index.php?topic=9489.msg139680#msg139680 ). Has that been addressed?

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