Perhaps I should have used different terminology; i.e. "device imaging" instead of "backup". The "Image" should consist of a single file, and it is created and written back to the device on a trusted pair of off-line Linux computers, with appropriate device imaging software installed, at two different locations. When the device is in transit between locations, it must be in the same state as it is when "restored to factory settings". I have no interest in the access of individual applications or data files.