private static byte[] randomBytes(){
  SecureRandom rng=new SecureRandom();
  byte[] result=new byte[32];
  rng.nextBytes(result);
  return result;
}

private static byte [ ] randomBytes ( ) { SecureRandom rng = new SecureRandom ( ) ; byte [ ] result = new byte [ 32 ] ; rng . nextBytes ( result ) ; return result ; }
generate a random byte [ ] of length 32
