HOTP

hotp.scala

def HMAC_SHA1(key: Array[Byte], text: Array[Byte]): Array[Byte] = {
  val mac = Mac.getInstance("HmacSHA1")
  mac.init(new SecretKeySpec(key, "RAW"))
  mac.doFinal(text)
}

def hton64(n: Long): Array[Byte] =
  (0 to 7)
    .map(i => (n >>> 8 * (7 - i)) & 0xff)
    .map(_.toByte)
    .toArray

def generateOTP(key: Array[Byte], movingFactor: Long, digits: Int): String = {
  val hash = HMAC_SHA1(key, hton64(movingFactor))
  val off  = hash.last & 0x0f
  var code = hash.slice(off, off+4).foldLeft(0) { (acc, b) => acc << 8 | (b & 0xff) }
  code &= 0x7fffffff
  code %= Math.pow(10, digits).toInt
  ("%0" + digits + "d").format(code)
}