A physically unclonable function (PUF) comprises a plurality of conductors, at least some of which are arranged so that they interact electrically and/or magnetically with one another. A media surrounds at least of portion of each of the conductors and further defines at least one cavity, where the cavity is structured to provide the device with an environmentally dependent characteristic. Circuitry applies an electrical challenge signal to at least one of the conductors and receives an electrical output from at least one of the other conductors to generate an identifying response to the challenge signal that is unique to the device.