Birds of the Same Feather Flock Together: A Dual-Mode Circuit Candidate for Strong PUF-TRNG Functionalities
Kuheli Pratihar, Urbi Chatterjee, Manaar Alam, Rajat Subhra Chakraborty, Debdeep Mukhopadhyay
Abstract
Physically Unclonable Functions (PUFs) and True Random Number Generators (TRNGs) are two highly useful hardware primitives to build up the root-of-trust for embedded devices in Internet-of-Things and Cyber-Physical System applications. These applications demand the primitives be lightweight, yet flexible. However, PUFs are designed to offer <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">repetitive and instance-specific</i> randomness, whereas TRNGs are expected to be <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">invariably</i> random. A challenging but thought-provoking problem from a hardware designer's perspective would be to design a circuit that serves the purpose of both PUF and TRNG depending on the exact requirement of the application. Here, we present a dual-mode PUF-TRNG design that utilises two different hardware-intrinsic properties, i.e., oscillatory metastability of Transition Effect Ring Oscillator (TERO) cell and propagation delay of a buffer within the cell to achieve this goal. A 48.62% reduction in area is accomplished due to the integration in comparison to separate instances of standalone PUFs/ TRNG designs, built from Programmable Delay Line (PDL) based Arbiter PUFs (APUFs) and TERO-TRNG. Our final design has a hardware footprint of 618 Look-Up Tables (LUTs) and 447 Flip-Flops (FFs). Furthermore, experimental analysis of the state-of-the-art modelling attacks, reliability attacks on the proposed PUF design shows a prediction accuracy of 55.37% and 50.14% respectively for 5.2M Challenge Response Pairs (CRPs). Additionally, the TRNG passes evaluation through National Institute of Standards and Technology (NIST) Special Publication (SP) 800-22 and German Federal Office for Information Security (BSI) Application Notes and Interpretation of the Scheme (AIS)-31 tests.