SoK

Abstract“Classical keys,” i.e., secret keys stored permanently in digital form in nonvolatile memory, appear indispensable in modern computer security—but also constitute an obvious attack target in any hardware containing them. This contradiction has led to perpetual battle between key extractors and key protectors over the decades. It is long known that physical unclonable functions (PUFs) can at least partially overcome this issue, since they enable secure hardware without the above classical keys. Unfortunately, recent research revealed that many standard PUFs still contain other types of “secrets” deeper in their physical structure, whose disclosure to adversaries breaks security as well: Examples include the manufacturing variations in SRAM PUFs, the power-up states of SRAM PUFs, or the signal delays in Arbiter PUFs. Most of these secrets have already been extracted in viable attacks in the past, breaking PUF-security in practice. A second generation of physical security primitives now shows potential to resolve this remaining problem, however. In certain applications, so-called Complex PUFs, SIMPLs/PPUFs, and UNOs are able to realize not just hardware that is free of classical keys in the above sense, but completely “secret-free” instead. In the resulting hardware systems, adversaries could hypothetically be allowed to inspect every bit and every atom, and learn any information present in any form in the system, without being able to break security. Secret-free hardware would hence promise to be innately and permanently immune against any physical or malware-based key-extraction: There simply is no security–critical information to extract anymore. Our survey and tutorial paper takes the described situation as starting point, and categorizes, formalizes, and overviews the recently evolving area of secret-free security. We propose the attempt of making hardware completely secret-free as promising endeavor in future hardware designs, at least in those application scenarios where this is logically possible. In others, we suggest that secret-free techniques could be combined with standard PUFs and classical methods to construct hybrid systems with notably reduced attack surfaces.

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Programmable access-controlled and generic erasable PUF design and its applications

Jin

Burleson

Dijk

et al. 2022

J Cryptogr Eng

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Physical Unclonable Functions (PUFs) have not only been suggested as a new key storage mechanism, but -in the form of so-called "Strong PUFs" -also as cryptographic primitives in advanced schemes, including key exchange, oblivious transfer, or secure multi-party computation. This notably extends their application spectrum, and has led to a sequence of publications at leading venues such as IEEE S&P, CRYPTO, and EUROCRYPT in the past. However, one important unresolved problem is that adversaries can break the security of all these advanced protocols if they gain physical access to the employed Strong PUFs after protocol completion. It has been formally proven that this issue cannot be overcome by techniques on the protocol side alone, but requires resolution on the hardware level -the only fully effective known countermeasure being so-called Erasable PUFs . Building on this work, this paper is the first to describe a generic method of how any given silicon Strong PUF with digital CRP-interface can be turned into an Erasable PUF. We describe how the Strong PUF can be surrounded with a trusted control logic that allows the blocking (or "erasure") of single CRP. We implement our approach, which we call "GeniePUF", on FPGA, reporting detailed performance data and practicality figures. Furthermore, we develop the first comprehensive definitional framework for Erasable PUFs. Our work so re-establishes the effective usability of Strong PUFs in advanced cryptographic applications, and in the realistic case, adversaries get access to the Strong PUF after protocol completion. As an extension to earlier versions of this work , we also introduce a generalization of Erasable PUFs in this paper, which we call Programmable Access Controlled PUFs (PAC PUFs). We detail their definition, and discuss various exemplary applications of theirs.

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SoK

Cited by 7 publications

References 63 publications

Physical Unclonable Functions

Physical Unclonable Functions

Secret-free security: a survey and tutorial

Programmable access-controlled and generic erasable PUF design and its applications

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