Comparative analysis of SRAM memories used as PUF primitives

In this publication we present the results of our investigations into the reliability and uniqueness of Static Random Access Memories (SRAMs) in different technology nodes when used as a Physically Unclonable Function (PUF). The comparative analysis that can be found in this publication is the first ever of its kind, using different SRAM memories in technologies ranging from 180nm to 65nm. Each SRAM memory presents a unique and unpredictable start-up pattern when being powered up. In order to use an SRAM as a PUF in an application, the stability of its start-up patterns needs to be assured under a wide variety of conditions such as temperature and applied voltage. Furthermore the start-up patterns of different memories must be unique and contain sufficient entropy. This paper presents the results of tests that investigate these properties of different SRAM memory technology nodes. Furthermore, it proposes the construction of a fuzzy extractor, which can be used in combination with the tested memories for extracting secure cryptographic keys.

I. Introduction

Due to deep-submicron manufacturing process variations every transistor in an Integrated Circuit (IC) has slightly different physical properties that lead to measurable differences in terms of its electronic properties like threshold voltage and gain factor. Since these process variations are uncontrollable during manufacturing, the physical properties of a device can neither be copied nor cloned. It is very hard, expensive and economically not viable to purposely create a device with a given electronic fingerprint. A Physically Unclonable Function (PUF) is an electronic circuit that measures the underlying fingerprint in the transistors that it is made of. Because of its dependency on the deep-submicron process variations, PUFs are very hard to reproduce by construction. However, in order to be able to use implementations of PUFs they should also be easy to challenge and their responses easy to measure.