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Physical Characterization of Arbiter PUFs

Shahin Tajik, Enrico Dietz, Sven Frohmann, Dmitry Nedospasov, Jean-Pierre Seifert, Clemens Helfmeier, Christian Boit, and Helmar Dittrich
Workshop on Cryptographic Hardware and Embedded Systems (CHES 2014)
Busan, Korea


As intended by its name, Physically Unclonable Functions (PUFs) are considered as an ultimate solution to deal with insecure storage, hardware counterfeiting, and many other security problems. However, many different successful attacks have already revealed vulnerabilities of certain digital intrinsic PUFs. Although settling-state-based PUFs, such as SRAM PUFs, can be physically cloned by semi-invasive and fully-invasive attacks, successful attacks on timing-based PUFs were so far limited to modeling attacks. Such modeling requires a large subset of challenge-response-pairs (CRP) to successfully model the targeted PUF. In order to provide a final security answer, this paper proves that all arbiter-based (i.e. controlled and XOR-enhanced) PUFs can be completely and linearly characterized by means of photonic emission analysis. Our experimental setup is capable of measuring every PUF-internal delay with a resolution of 6 picoseconds. Due to this resolution we indeed require only the theoretical minimum number of linear independent equations (i.e. physical measurements) to directly solve the underlying inhomogeneous linear system. Moreover, we neither require to know the actual PUF challenges nor the corresponding PUF responses for our physical delay extraction. On top of that devastating result, we are also able to further simplify our setup for easier physical measurement handling. We present our practical results for a real arbiter PUF implementation on a Complex Programmable Logic Device (CPLD) from Altera manufactured in a 180 nanometer process.