Hello,

today I want to show, how blockchain random generator can be used for lottery validation.

Specifically at: https://freebitco.in/?r=28730542

The site is combination of faucet and some gambling for satoshis (no deposit necessary, and I was able to withdraw without issues).

As one part of gambling there is interesting loterry (you can get some small number of free tickets, or purchase some).

Of course its hard to believe in fair draw at some web site, so blockchain is used as public random generator.

(of course full smart contract would be even better, but also harder to use and overkill for just a faucet and gamling for few satoshis)

So how does it work?

- before the draw is started, server seed is created and SHA256 displayed to public (so you can validate later exact value of the seed, but you cannot see the seed itself in advance)

- all user tickets are sorted and put into a file

- file is announced in public with timestamp

- at same time as a file, the number of bitcoin block in future is selected and annunced

- when the selected block is mined, its hash is used as client seed

- then string is created "server seed:client seed:number of price" -> SHA256 of this string is calculated

- the first 8 digits of last has is taken, converted to decimal and points to winning ticket

- as you can see, the server side selected part of keys in advance and does not select other part (its come from bitcoin block in future)

- the rest of calculation and source data is public and announced before the draw -> making it close to imposible to affect the draw

So in same way you can agree on safe and remote random generator with anyone. Simply agree on block in future and some formula how to convert it into required interval.

For this week we can see nice prices and my not so nice chance to win one of those: