alexcambose/provably-fair-example

Provably fair implementation done in javascript.

Provably fair example

A provably fair example build with express, and plain javascript.

What is provably fair

A provably fair algorithm allows users to check and analyze the legitimacy of every roll and confirm that the server/house did not alter them in their favor. By using a provably fair algorithm to generate random numbers neither players nor the operator of the site can know the result of the game before it starts.

For more information about the techincal details of the implementation check out this article

Provably fair system in javascript - What is and how to build a provably fair system in javascript

Getting Started

Prerequisites

Nodejs 8+ installed

Installation

Clone this repo

$ npm install

How to use?

$ npm run start

Open you favourite browser on localhost:3000.

License

This project is licensed under the MIT License - see the LICENSE file for details

provably-fair-example's Issues

In this implementation 99 has biggest roll chance

Correct me if I am wrong, but I think 99 will have biggest chance to be rolled, because it has chance of being rolled as every other number + chance that all substrings converted to number will be over 1e6.

const getResult = hashedValue => {
  // the offset of the interval
  let index = 0;
  // result variable
  let result;

  do {
    // get the decimal value from an interval of 5 hex letters
    result = parseInt(hashedValue.substring(index * 5, index * 5 + 5), 16);
    // increment the offset in case we will need to repeat the operation above
    index += 1;
    // if all the numbers were over 999999 and we reached the end of the string, we set that to a default value of 9999 (99 as a result)
    if (index * 5 + 5 > 129) {
      result = 9999;
      break;
    }
  } while (result >= 1e6);
  // the result is between 0-999999 and we need to convert if into a 4 digit number
  // we a apply a modulus of 1000 and the 4 digit number is further split into a 2 digit number with decimals
  return [result % 1e4] * 1e-2;
};

Confusing typo

https://github.com/alexcambose/provably-fair-example/blob/master/routes/api.js#L19

 * It doesn't return the hashed serverseed in advance, because that would
 * allow the client to generate all the rolls in advance.

Should be:

 * It doesn't return the *unhashed* serverseed in advance, because that would
 * allow the client to generate all the rolls in advance.