I think we have left this level a long time ago where one could answer: The system is in a physically secured location. As long as there is no physical access i

I think we have left this level a long time ago where one could answer: The system is in a physically secured location. As long as there is no physical access it should be safe. See mobiles like iPhones, gaming devices like XBox, Playstation etc. authenticators like chipcards or security token and HSM. All have to asume that the attacker has physical access to the device. Security Engineering Ch. 16 "Physical Tamper Resistance" is a good read for some special classes of devices. But I would recommend all topics from this book even unrelated to this thread. ;)