higher order dpa attacks since higher order dpa attacks require more power consumption waveforms than basic dpa attacks dynamic masking can still be of some advantage while the described defences improve resistance to a range of side channel attacks they also reduce the qa chips vulnerability to a range of other physical attacks such as focused ion beam chip modifications this is because if the base key value only moves from the non volatile memory cell into other circuitry very few times over the life of the ink cartridge then very little key information can practically be obtained for each difficult chip modification probing it is very difficult to directly measure the electrical charge on a tiny non volatile memory cell containing a key bit unless it is read from the memory an additional set_qa_device_id command can be added to make the use of base keys more explicit this command would communicate the appropriate qa chip identifier for the checking device for a selected base key or set of base keys cause the calculation of one or a set of variant keys and cause the caching of the variant key s for later use the number of variant key generations allowed in the improved qa chip can be restricted by using a virtual consumable vc a virtual consumable is a qa chip field that indicates.