Keygen.js

const t = [37, 40, 99, 4, 21, 203, 69, 9, 191, 57, 183, 0, 38, 97, 237, 75, 85, 246, 207, 3, 104, 128, 173];
function valid(s) {
  return s.length === t.length &&
    [...s].every((ch, i) => (ch.charCodeAt(0) * 7 + i * 3) % 256 === t[i]);
}