code: private static byte[] padBytes(byte[] bytes, int length) {
  		byte[] padded = new byte[length];
  		for (int i = 0; i < bytes.length; i++) {
  			padded[i] = bytes[i];
  		}
  		return padded;
  	}
docs: Return array with length size, if length is greater than the previous
  size, the array is zero-padded at the end.
  
  @param bytes
  @param length
  @return zero-padded array with length size