verify.js

const crypto = require("crypto");

const terminatingHash =
  "86728f5fc3bd99db94d3cdaf105d67788194e9701bf95d049ad0e1ee3d004277";
const salt = "0000000000000000004d6ec16dafe9d8370958664c1dc422f452892264c59526";
function* genHashChain(hash) {
  for (let i = 0; hash !== terminatingHash; i++) {
    if (i > 10e6) {
      throw new Error("Could not find terminating hash, wrong hash chain?!");
    }

    yield hash;
    hash = crypto.createHash("sha256").update(hash).digest("hex");
  }
}
function calcGameId(hash) {
  let count = 0;
  for (const _ of genHashChain(hash)) {
    count++;
    if (count > 10e6) {
      throw new Error("not part of canonical chain?!");
    }
  }
  return count;
}
function gameResult(seed) {
  const nBits = 52; // number of most significant bits to use
  const hmac = crypto.createHmac("sha256", salt);
  hmac.update(Buffer.from(seed, "hex"));
  const r = parseInt(hmac.digest("hex").slice(0, nBits / 4), 16);
  let X = r / Math.pow(2, nBits); // uniformly distributed in [0; 1)
  X = 99 / (1 - X);
  const result = Math.floor(X);
  return Math.max(1, result / 100);
}
const seed = process.argv[2];
let gameId = calcGameId(seed);
for (const hash of genHashChain(seed)) {
  console.log(
    `game id ${(gameId--).toString()} \t ${hash} \t ${gameResult(hash).toFixed(
      2
    )}x`
  );
}