Provably-fair

Dead simple generator for provably fair gambling. Entirely callback, we need performance here. Uses a new server seed on each bet to provide verification capabilty to the client right after he gets the result.

Provably-fair logic

The idea is to generate a reproductible result that is defined in advance to prevent the server from cheating. To achieve this, we must :

• create a server seed and pass the hash of that seed to the client before he gambles;
• receive a client seed generated by the client;
• concat the two seeds to get only one;
• create the bet result from a random generator seeded with our concatenated seed.
• send the result to client, along with the original server seed.

This way, the client will be able to :

• make sure the server seed we used to generate the result is indeed the one we sent him as a hash (he can hash it himself to compare);
• reproduce the same bet result by reproducing the whole process.

Getting Started

Install

npm i --save provably-fair

API

• generateServerSeedHash({ userId = 'none', expiresIn = 60 * 60 }) stores server seed with redis & returns the seed hash to pass to client.
• createAndChallenge({ userId = 'none', expiresIn = 60 * 60, serverSeedHash, clientSeed, guess, customResult, customValidation }, callback) creates a new bet and compares the result with the client guess, then deletes the server seed redis key to prevent reuse. Returns (err, valid, bet);
• verify({ serverSeed, clientSeed, customResult }, callback) returns serverSeedHash of provided serverSeed & reproduces bet result.

require('provably-fair')(client)

• Initialize provablyFair
• client Required: Redis client

generateServerSeedHash(options)

• options <Object>
  • userId Default: none - unique client identifier
  • expiresIn Default: 60 * 60
• returns hash hash of the securely stored with Redis serverSeed.

createAndChallenge(options, callback)

• options <Object>
  • userId Default: none - unique client identifier
  • expiresIn Default: 60 * 60
  • serverSeedHash Required
  • clientSeed Required
  • guess Required
  • customResult Default: function(randomNumber) { return randomNumer }
  • customValidation Default: function(guess, result) { return guess === result }
• callback <Function> returns (err, valid, bet)
  • valid <Boolean> whether or not captcha is solved
  • bet <Object>
    • id bet ID
    • result bet result
    • serverSeed
    • clientSeed

Example : Gobelet game

The client must guess a number between 1 and 10. Test it on RunKit.

// Init
const redis = require('redis');
const client = redis.createClient();

const provablyFair = require('provably-fair')(client);

// default return randomNumber
const gobeletResult = function (randomNumber) {
  return Math.floor(randomNumber * 10) + 1;
};

// this is default
const gobeletValidation = function (guess, result) {
  return guess === result;
};

// Generate & send before client gambles;
const serverSeedHash = provablyFair.generateServerSeedHash();

// Retrieve the serverSeedHash & these values from the client :
const clientSeed = 'clientSeed';
const guess = 5;

// We create & challenge the bet
provablyFair.createAndChallenge({
  serverSeedHash,
  clientSeed,
  expiresIn: 60 * 60,
  guess,
  customResult: gobeletResult,
  customValidation: gobeletValidation
}, (err, valid, bet) => {
  // returns true if guess is correct
  // bet = { serverSeed, clientSeed, result } can be passed to the client
  // for verification (along with your customResult resolver)
});

Todo

Client plugin for verification.