buffer[4] = 0x55;
    buffer[4] ^= buffer[0];
    buffer[4]  = (buffer[4]<<1 | buffer[4]>>7);
    buffer[4] ^= buffer[1];
    buffer[4]  = (buffer[4]<<1 | buffer[4]>>7);
    buffer[4] ^= buffer[2];
    buffer[4]  = (buffer[4]<<1 | buffer[4]>>7);
    buffer[4] ^= buffer[3];
    buffer[4]  = (buffer[4]<<1 | buffer[4]>>7);