*    @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.
        for (int i = 0; i < 16; i++)
            X[i] = (block[offset++] & 0xFF)       |
                   (block[offset++] & 0xFF) <<  8 |