code: protected void xor(byte[] dest, byte[] src)
      {
          for (int i = 0; i < dest.length; i++)
          {
              dest[i] ^= src[i];
          }
      }
docs: Block-Xor. Xor source bytes into destination byte buffer. Destination
  buffer must be same length or less than source buffer.
  
  @param dest destination byte buffer
  @param src source bytes