Physically Unclonable Functions: A Study on the State of the Art and Future Research Directions

The idea of using intrinsic random physical features to identify objects, systems and people is not new. Fingerprint identification of humans dates at least back to the nineteenth century [20] and led to the field of biometrics. In the eighties and nineties of the twentieth century, random patterns in paper and optical tokens were used for unique identification of currency notes and strategic arms [2, 49, 7]. A formalization of this concept was introduced in the very beginning of the twenty first century, first as physical one-way functions [38, 39], physical random functions [12] and finally as physical(ly) unclonable functions or PUFs. In the years following this introduction, an increasing number of new types of PUFs were proposed, with a tendency towards more integrated constructions. The practical relevance of PUFs for security applications was recognized from the start, with a special focus on the promising properties of physical unclonability and tamper evidence. Over the last couple of years, the interest in PUFs has risen substantially, making them a hot topic in the field of hardware security and leading to an expansion of published results. In this work we have made, to the best of our knowledge, an extensive overview of all PUF and PUF-like proposals up to date in an attempt to get a thorough understanding of the state of the art in this topic. Due to the wide variety of different proposals, the different measures used for assessing them and the different possible application scenarios, making an objective comparison between them is not a trivial task. In order