@derin-n/provablyfair/provablyfairhost.js

A provably fair algorithm

//you will need to generate your own host seed, you can generate it via the method below
//generate one seed, one of them will be your host seed, hold onto it
//the game hash will be created in the browser and sent to the server
const generateRandomSeed = function (callback) {

    //randomly generate 1000 bytes of data
    crypto.randomBytes(1000, (err, randomData) => {

        if (err) throw err;
        //define hasher
        let hashedSeed = crypto.createHash("sha512");
        //convert the data to string and hash it
        hashedSeed.update(randomData.toString('hex'));
        //digest the hash into a string
        let digestSeed = hashedSeed.digest('hex');

        callback(digestSeed);

    });

}

//generate results from hashes
//for example, get the game seed from the client with a socket, and pass it to this function
const generateResult = function (hostSeed, gameSeed, callback) {
    //create hasher
    let combinedHash = crypto.createHash('sha512');
    //combine the host seed with the game seed
    let concatHash = hostSeed + gameSeed;
    //hash the combination
    combinedHash.update(concatHash);
    //digest the hash into a string
    let combinedHashHex = combinedHash.digest('hex');
    //define result 
    let result = "";
    //result will be converted into numbers
    let numberResult;
    //for every char in the string
    for (let i = 0; i < combinedHashHex.length; i++) {
        //get the char
        let singleChar = combinedHashHex.charAt(i);
        //check if number and result has less than 2 number chars
        if (!(isNaN(singleChar)) && result.length < 2) {
            //turn char into number
            numberChar = parseInt(singleChar);
            //add the char to result
            result += singleChar;
        }
        //when result has two numbers, the first one can be zero
        if (result.length == 2) {
            //convert into number
            numberResult = parseInt(result);
            //callback with the numerical result
            callback(numberResult);
            return;
        }
    }
}