Controlled physical random functions and applications

Abstract

The cryptographic protocols that we use in everyday life rely on the secure storage of keys in consumer devices. Protecting these keys from invasive attackers, who open a device to steal its key, is a challenging problem. We propose controlled physical random functions (CPUFs) as an alternative to storing keys and describe the core protocols that are needed to use CPUFs. A physical random functions (PUF) is a physical system with an input and output. The functional relationship between input and output looks like that of a random function. The particular relationship is unique to a specific instance of a PUF, hence, one needs access to a particular PUF instance to evaluate the function it embodies. The cryptographic applications of a PUF are quite limited unless the PUF is combined with an algorithm that limits the ways in which the PUF can be evaluated; this is a CPUF. A major difficulty in using CPUFs is that you can only know a small set of outputs of the PUF-the unknown outputs being unrelated to the known ones. We present protocols that get around this difficulty and allow a chain of trust to be established between the CPUF manufacturer and a party that wishes to interact securely with the PUF device. We also present some elementary applications, such as certified execution.

A Survey on Lightweight Entity Authentication with Strong PUFs

“…Controlled PUFs [13][14][15][16] provide reinforcement against modeling via a cryptographic hash function (oneway). Two instances, preceding and succeeding the PUF respectively, are shown in Figure 7(b).…”

Fault Injection Modeling Attacks on 65 nm Arbiter and RO Sum PUFs via Environmental Changes

“…So-called controlled PUFs enhance the security of CRP-based authentication via additional hardware [2]. Hereby, the response bits of the strong PUF are post-processed using a fuzzy extractor.…”

Flowchart description of security primitives for controlled physical unclonable functions

“…In effect, the CPUF is a sort of trusted computing environment. In Gassend et al [6,7,8] a way was presented to employ this trusted environment for the purpose of outsourcing computations. The idea is roughly as follows.…”

“…In the construction of [6] the proof is verifiable only by the user who sends the task to the CPUF. In [8] this was generalized to a proof ('E-proof') that can be verified by third parties as well. The above scheme provides a way for users to outsource computations and be certain that their program was correctly executed, by the designated device, yielding the given result.…”

“…Instead, the security is based on the secrecy of the CRPs. In addition to the proof generation, [6,7,8] also provide a number of protocols for CRP management, most notably bootstrapping (creation of the original CRPs) and renewal (allowing a user who possesses a CRP to obtain more CRPs). For an overview of PUFs, CPUFs, and fuzzy extractors we refer to [14].…”