Using Unstable SRAM Bits for Physical Unclonable Function Applications on Off-The-Shelf SRAM

Physical Unclonable Function (PUF) is recently used in modern electronic systems for device authentication and secret key generation. SRAM PUF is a popular memory-based PUF because it is a standard component for most electronic devices. Previously only strongly stable RAM bits are selected as PUF bits in order to achieve high reliability, hence requiring relatively large SRAM. Furthermore, SRAM PUF might suffer from PUF clone attack for using stable bits. Attackers may use Photon Emission Analysis (PEA) to observe the behavior of the stable bits and conducted Focused Ion Beam circuit edit (FIBCE) to produce an identical physical response. In this paper, we propose a new method that employs unstable bits as PUF bits in addition to the stable bits to increase the SRAM bit usage rate. We also show that this method can efficiently resist the PUF clone attack. Experimental results show that even though our proposed method uses unstable bits as PUF bits, it can still achieve high reliability. It can reach an average 2% intra-HD without Error Correction Code (ECC) under various conditions and an average inter-HD of 49.33%.

I. Introduction

Many Physical Unclonable Functions (PUFs) have been proposed and implemented in recent years, such as Ring-Oscillator PUF, Arbiter PUF, Optical PUF, Coating PUF, SRAM PUF [1], etc. Among these PUFs, SRAM PUF is a popular one because SRAM is a standard component in most electronic devices and has sufficient randomness that makes it suitable for generating a secret key. When an SRAM cell is turned on without a reset, it may be biased toward 0 or 1 based on manufacturing process variation.