Long-term continuous assessment of SRAM PUF and source of random numbers

TL;DR

This study conducts a two-year long-term assessment of SRAM PUFs on Arduino boards, revealing that aging slightly reduces reliability but improves randomness, providing more realistic insights into device performance over time.

Contribution

It presents the first long-term real-world aging analysis of SRAM PUFs, contrasting accelerated tests and showing more accurate effects of aging under nominal conditions.

Findings

Bit flips increased by 19.3% after two years.

Min-entropy of SRAM PUF noise improved by 19.3%.

Reliability degradation was less than previously estimated.

Abstract

The qualities of Physical Unclonable Functions (PUFs) suffer from several noticeable degradations due to silicon aging. In this paper, we investigate the long-term effects of silicon aging on PUFs derived from the start-up behavior of Static Random Access Memories (SRAM). Previous research on SRAM aging is based on transistor-level simulation or accelerated aging test at high temperature and voltage to observe aging effects within a short period of time. In contrast, we have run a long-term continuous power-up test on 16 Arduino Leonardo boards under nominal conditions for two years. In total, we collected around 175 million measurements for reliability, uniqueness and randomness evaluations. Analysis shows that the number of bits that flip with respect to the reference increased by 19.3% while min-entropy of SRAM PUF noise improves by 19.3% on average after two years of aging. The impact of aging on reliability is smaller under nominal conditions than was previously assessed by the accelerated aging test. The test we conduct in this work more closely resembles the conditions of a device in the field, and therefore we more accurately evaluate how silicon aging affects SRAM PUFs.