The foil-based solution consists of patterned metal electrodes embedded into a polymer film with a self-adhesive backing. The electrodes are connected to the board to be protected and special read-out software IP running on the board's controller can extract the PUF from the film as is has been wrapped around or stuck to the board.
Try to remove the PUF sticker, pinch it to probe through it, scratch it or unseal it and the PUF will be altered. By detecting that change, the circuit board will be able to take any counter-measure it will have been programmed for, for example sending an alert message and disabling itself at run-time, or wiping out all of its embedded software.
Showing a demo at Embedded World, Fraunhofer AISEC’s head researcher on the so-called PEP project (Protecting Electronic Products, maybe with a pun intended on Polyethylene Plastics), Sven Plaga didn’t want to say too much about the internals of the film.
“Now we are exploring electrode patterns of different shapes and complexities as well as correction algorithms to ensure the PUF’s stability over time and across different temperatures as the film could shrink or expand”.
For the researchers, it is all about finding the right trade-off between PUF complexity and stability, but they are investigating different sizes and they expect the PUF foil to be produced cheaply in a roll-to-roll printing process.
“The advantage over silicon-based PUFs is that one foil could protect an entire board or system, it is also much cheaper and simpler to implement”, he added, saying such a PUF sticker may be commercialised within the next two to three years.
As was the case in the booth demonstration, the foil could even extend outside an electronic enclosure or be part of a seal to detect its opening. In that case the plastic PUF provides not only a unique key for securing on-board communications, it could also serve for early external