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A measurement system for capacitive PUF-based security enclosures

: Obermaier, J.; Immler, V.; Hiller, M.; Sigl, G.


Institute of Electrical and Electronics Engineers -IEEE-; Association for Computing Machinery -ACM-; Electronic Design Automation Consortium -EDAC-:
55th Annual Design Automation Conference, DAC 2018. Proceedings : San Francisco, CA, USA, June 24-29, 2018
New York: ACM, 2018
ISBN: 978-1-4503-5700-5
Design Automation Conference (DAC) <55, 2018, San Francisco/Calif.>
Fraunhofer AISEC ()

Battery-backed security enclosures that are permanently monitored for penetration and tampering are common solutions for providing physical integrity to multi-chip embedded systems. This paper presents a well-tailored measurement system for a batteryless PUF-based capacitive enclosure. The key is derived from the PUF and encrypts the underlying system. We present a system concept for combined enclosure integrity verification and PUF evaluation. The system performs differential capacitive measurements inside the enclosure by applying stimulus signals with a 180° phase shift that isolate the local variation in the femtofarad range. The analog circuitry and corresponding digital signal processing chain perform precise PUF digitization, using a microcontroller-based digital lock-in amplifier. The system's measurement range is approximately ±73 fF, the conversion time per PUF node is less than 0.6 ms, and the raw data shows a measurement noise of 0.3 fF. This is the base for a high-entropy key generation while enabling a short system startup time. The system is scalable to the enclosure size and has been experimentally verified to extract information from 128 PUF nodes, using a system prototype. The results show that our concept forms a cornerstone of a novel batteryless PUF-based security enclosure.