*    <p>
     *    Transforms context based on 512 bits from input block starting
     *    from the offset'th byte.
     *
     *    @param    block    input sub-array.
     *    @param    offset    starting position of sub-array.
     */
    private void transform (byte[] block, int offset) {

        // encodes 64 bytes from input block into an array of 16 32-bit
        // entities. Use A as a temp var.