PUFs in Security Protocols: Attack Models and Security Evaluations

Abstract

In recent years, PUF-based schemes have not only been suggested for the basic security tasks of tamper sensitive key storage or system identification, but also for more complex cryptographic protocols like oblivious transfer (OT), bit commitment (BC), or key exchange (KE). In these works, so-called "Strong PUFs" are regarded as a new, fundamental cryptographic primitive of their own, comparable to the bounded storage model, quantum cryptography, or noisebased cryptography. This paper continues this line of research, investigating the correct adversarial attack model and the actual security of such protocols.In its first part, we define and compare different attack models. They reach from a clean, first setting termed the "stand-alone, good PUF model" to stronger scenarios like the "bad PUF model" and the "PUF re-use model". We argue why these attack models are realistic, and that existing protocols would be faced with them if used in practice. In the second part, we execute exemplary security analyses of existing schemes in the new attack models. The evaluated protocols include recent schemes from Brzuska et al. published at Crypto 2011 [1] and from Ostrovsky et al. [18]. While a number of protocols are certainly secure in their own, original attack models, the security of none of the considered protocols for OT, BC, or KE is maintained in all of the new, realistic scenarios.One consequence of our work is that the design of advanced cryptographic PUF protocols needs to be strongly reconsidered. Furthermore, it suggests that Strong PUFs require additional hardware properties in order to be broadly usable in such protocols: Firstly, they should ideally be "erasable", meaning that single PUF-responses can be erased without affecting other responses. If the area efficient implementation of this feature turns out to be difficult, new forms of Controlled PUFs [8] (such as Logically Erasable and Logically Reconfigurable PUFs [13]) may suffice in certain applications. Secondly, PUFs should be "certifiable", meaning that one can verify that the PUF has been produced faithfully and has not been manipulated in any way afterwards. The combined implementation of these features represents a pressing and challenging problem, which we pose to the PUF hardware community in this work.

Universally Composable Secure Computation with (Malicious) Physically Uncloneable Functions

“…To reiterate, the "attacks" presented in points 5 and 6 are not attacks on the protocols presented in this paper. It was already known (from the work of [CF01,CKL03]) and mentioned in our work before [RvD13] appeared, that our protocols are not secure in other attack models. Indeed in the standard model (i.e., when no honest PUF exists and malicious PUFs can always communicate with their creators) our protocols can not be UC secure as UC security is impossible in the standard model.…”

“…A recent paper by van Dijk and Ruhrmair [RvD13] claims certain "attacks" on protocols presented in this paper. We discuss their claims in this section.…”

“…The "attacks" on our protocols are noted in points 3, 5 and 6 in the Our Results subsection of Section I of [RvD13]. We will discuss the attacks mentioned in points 5 and 6 first.…”

“…As is clearly stated by the authors of [RvD13] themselves in their paper multiple times 5 , attacks in points 5 and 6 are "[..] outside the original attack models of the respective papers." This means that their attacks use properties of PUFs not present in our model, and therefore, have no consequence on the security of our protocols.…”

Modeling and Design of Ring Oscillators and their Application in Radiation Environments

“…The physical behavior of a PUF can be modeled mathematically [RvD13,MRMK13]. This way, an equivalent circuit to a specific PUF can be designed to replace the genuine device.…”