code: static void zero(byte[] bytes, int off, int len) {
      // this is significantly faster than looping or Arrays.fill (which loops), particularly when
      // the length of the slice to be zeroed is <= to ARRAY_LEN (in that case, it's faster by a
      // factor of 2)
      int remaining = len;
      while (remaining > ARRAY_LEN) {
        System.arraycopy(ZERO_ARRAY, 0, bytes, off, ARRAY_LEN);
        off += ARRAY_LEN;
        remaining -= ARRAY_LEN;
      }
  
      System.arraycopy(ZERO_ARRAY, 0, bytes, off, remaining);
    }
docs: Zeroes all bytes between off (inclusive) and off + len (exclusive) in the given array.