A portable storage device, for example a secure smart card, contains network identification information and configuration information for a processing unit that is connectable to a data communications network, which processing unit includes a device reader for reading the portable storage device. The portable storage device includes storage and an access controller. The storage holds a network identity and configuration information for the processing unit and at least one encryption key. The access controller is operable to control access to the storage by implementing key-key encryption. An embodiment of the invention thus provides a medium not only for storing a network identity and configuration information for processing unit, but also for other secure information such as an encryption key associated therewith.