The winning ticket (random number) is generated before the game starts. Then along with random generated salt its crypted with MD5 function into round hash, which is displayed in begining of the game.
this.randomnumber = Math.random(); this.salt = getsalt(); this.roundhash = crypto.createHash('md5').update(this.randomnumber.toString() + this.salt).digest('hex');
At the end of the round salt and random number is revealed along with winner.
If you take (round number + salt) and run it through MD5 generator (for example md5.cz) you will recieve the round hash. Round hash is generated before the round starts so there is no way to manipulate the winning ticket.