Dan Kaminsky's DefCon RNG challenge

oi.js

#!/usr/bin/env node

/**
 * Forked from https://gist.github.com/PaulCapestany/6148566. Changes:
 *   - Beautified code
 *   - NodeJS-specific (will not work in the browser)
 *   - Scope variables with let and const keywords
 *   - 256-bit RNG
 *   - Remove von Neumann debiasing
 *   - Remove byte assembly
 *   - Debiases output with SHA-256
 *
 * Theory:
 *   Coin flipping measures a slow system (how many seconds it takes a coin to
 *   rise and fall) against a fast system (how many spins a coin can complete
 *   before it lands).
 *   
 *   This can be done in code. The slow system is a millisecond timer of 1000
 *   cycles/second. The fast system is the CPU itself of billions of
 *   cycles/second. Because interrupts aren't cycle accurate, the bit flips are
 *   irregular and unpredictable.
 *   
 *   This RNG has precedence with Matt Blaze's Truerand and Dan Kaminsky's
 *   DakaRand. See:
 *     - https://github.com/ab300819/applied-cryptography/blob/master/Cryptix-1.16/Math-TrulyRandom/truerand.c
 *     - https://dankaminsky.com/2012/08/15/dakarand/
 *
 * Application:
 *   256 "coin flips" are generated, hashed with SHA-256, encoded as
 *   hexadecimal, and printed to the screen.
 *
 *   This code is slow, taking ~0.6 seconds on my Intel Core i7-8650 @ 1.90GHz.
 */

const { createHash } = require("crypto")

function millis() {
  return Date.now()
}

function flip_coin() {
  let n = 0
  const then = millis() + 1
  while(millis() <= then) n ^= 1
  return n
}

function sha256_hash(str) {
  return createHash("sha256").update(str).digest("hex")
}

function main() {
  let n = 256
  let flips = ""
  while(n--) flips += flip_coin()
  return sha256_hash(flips)
}
 
if (require.main === module) {
  console.log(main())
}