1. A device comprising: application circuitry; one or more scan or boundary scan components adapted to shift in and shift out test scans of the application circuitry; a unique code adapted to uniquely identify the device; an interrogation code component adapted to interact with interrogation information having an interrogation code applied to the device; a hidden seed element which is of unique value per device of a given type, used in a signature generation process for the device, wherein the hidden seed is involved with though not directly accessible during authentication of the device, not extractable from the device, and initially known only to an IC fabricator that fabricated the device; a signature encryption component that provides an output signature code that is unique to the device, for given interrogation information, the output signature code being a function of the hidden seed; wherein the device and/or signature encryption engine are configured to process a test/scan procedure performed on the device, the test/scan procedure comprising: shifting in and shifting out, via one or more scan or boundary scan components, test scans of the application circuitry, each test scan comprising the interrogation information; performing a signature generation process within the device, via the signature encryption component, using the hidden seed element which is of unique value per device of a given type, the signature being a function of algorithmic interaction with at least the hidden seed and the interrogation code, and consisting of a signature code based only on the algorithmic interaction such that the hidden seed is not discernable from the signature code, wherein the hidden seed element is not extractable from the device, and is initially known only to the IC fabricator that fabricated the device; and providing the signature code that is unique to the device, for given interrogation information as output, wherein authenticity of the signature code can only be determined by knowledge of the device's hidden seed and the interrogation code; wherein, as a function of (i) the hidden seed being inaccessible from the device and unlearnable during authentication via the interrogation codes of the test/scan procedure and (ii) ability to perform the test scans without knowing the hidden seed, the device is counterfeit-resistant.