bustabit.com v2 history generation

main.js

const { createHash, createHmac } = require("crypto");

const salt = "0000000000000000004d6ec16dafe9d8370958664c1dc422f452892264c59526"; // chosen in seeding event: https://bitcointalk.org/index.php?topic=2807542.msg28778130#msg28778130

let [id, hash] = process.argv.slice(2);

id = Number(id);
if (Number.isNaN(id) || !Number.isSafeInteger(id) || id < 1) {
  printUsageMessage();
  process.exit(1);
}

const isSha256Hash = /^[0-9a-f]{64}$/i.test(hash);
if (!isSha256Hash) {
  printUsageMessage();
  process.exit(1);
}
hash = Buffer.from(hash, "hex");

console.log("id,hash,result");
for (; id > 0; id--) {
  const result = gameResult(hash, salt);
  console.log(`${id},${hash.toString("hex")},${result}`);

  hash = sha256(hash.toString("hex"));
}
console.error(`The terminating hash is ${hash.toString("hex")}.`);

function gameResult(seed, salt) {
  const nBits = 52; // number of most significant bits to use

  // 1. HMAC_SHA256(key=salt, message=seed)
  const hmac = createHmac("sha256", salt);
  hmac.update(seed);
  seed = hmac.digest("hex");

  // 2. r = 52 most significant bits
  seed = seed.slice(0, nBits / 4);
  const r = parseInt(seed, 16);

  // 3. X = r / 2^52
  let X = r / Math.pow(2, nBits); // uniformly distributed in [0; 1)

  // 4. X = 99 / (1-X)
  X = 99 / (1 - X);

  // 5. return max(trunc(X), 100)
  const result = Math.floor(X);
  return Math.max(1, result / 100);
}

function printUsageMessage() {
  console.error(`Usage: node main.js <game_id> <hash>
Example: node main.js 1152006 01ad6c6988689c103b4cf6ed84e8a14b1c38ef48c26abc44fb97874f36be4e02`);
}

function sha256(value) {
  return createHash("sha256")
    .update(value)
    .digest();
}