This paper discusses the practical implementation of a novel security tool termed SIMPL system, which was introduced in [1]. SIMPL systems can be regarded as a public key version of physical unclonable functions (PUFs). Like the latter, a SIMPL system S is physically unique and nonreproducible, and implements an individual function F S . In opposition to a PUF, however, a SIMPL system S possesses a publicly known numerical description, which allows its digital simulation and prediction. At the same time, any such simulation must work at a detectably lower speed than the real-time behavior of S. As argued in [1], SIMPL systems have certain practicality and security advantages in comparison to PUFs, certificates of authenticity, physically obfuscated keys, and also to standard mathematical cryptotechniques.In [1], definitions, protocols, and optical implementations of SIMPL systems were presented. This manuscript focuses on concrete electrical, integrated realizations of SIMPL systems, and proposes two potential candidates: SIMPL systems derived from special SRAM-architectures (socalled "skew designs" of SRAM cells), and implementations based on Cellular Non-Linear Networks (CNNs).
IntroductionPhysical Unclonable Functions (PUFs) are a relatively young, emerging cryptographic primitive [2,3,4,5,6,7]. However, one potential downside of PUF-based protocols is that they usually require a previously shared piece of information (typically some challenge-response-pairs) that was established in a joint set-up phase between the communicants. Alternatively, an online connection to a trusted authority at the time of the protocol execution must be employed. In this particular structural aspect, PUFs are resemblant of classical private key systems.In this paper, we are concerned with an alternative security tool called SIMPL systems, which is a public key version of standard PUFs. SIMPL systems have been introduced in [1]. The acronym SIMPL stands for "SIMulation Possible, but Laborious", and hints at the critical security feature of these structures. A physical system S is called a SIMPL system if the following holds:1. It is possible for everyone to numerically simulate and, thus, to predict the physical behaviour of S with very high accuracy. The basis of the simulation is an individual description D(S) of S, and a generic simulation algorithm Sim, which are both publicly known.