[Paper Review] Highly-Secure Physically Unclonable Cryptographic Primitives Using Nonlinear Conductance and Analog State Tuning in Memristive Crossbar Arrays

Hussein Nili, Gina C. Adam+5 more|arXiv (Cornell University)|Nov 23, 2016

Advanced Memory and Neural Computing37 references3 citations

TL;DR

This paper proposes a highly secure, reconfigurable physical unclonable function (PUF) primitive using 3D memristive crossbar arrays with nonlinear I-V characteristics and analog conductance tuning. By exploiting process-induced variations in 250-nm half-pitch memristors, the prototype achieves near-ideal uniformity (50% ± 5%) and diffusivity, with a low bit error rate of ~1.5% over 30 days under power supply variations, enabling over 10^19 unique challenge-response pairs.

ABSTRACT

The rapidly expanding hardware-intrinsic security primitives are aimed at addressing significant security challenges of a massively interconnected world in the age of information technology. The main idea of such primitives is to employ instance-specific process-induced variations in electronic hardware as a source of cryptographic data. Among the emergent technologies, memristive devices provide unique opportunities for security applications due to the underlying stochasticity in their operation. Herein, we report a prototype of a robust, dense, and reconfigurable physical unclonable function primitives based on the three-dimensional passive metal-oxide memristive crossbar circuits, by making positive use of process-induced variations in the devices' nonlinear I-Vs and their analog tuning. We first characterize security metrics for a basic building block of the security primitives based on a two layer stack with monolithically integrated 10x10 250-nm half-pitch memristive crossbar circuits. The experimental results show that the average uniformity and diffusivity, measured on a random sample of 6,000 64-bit responses, out of ~697,000 total, is close to ideal 50% with 5% standard deviation for both metrics. The uniqueness, which was evaluated on a smaller sample by readjusting conductances of crosspoint devices within the same crossbar, is also close to the ideal 50% +/- 1%, while the smallest bit error rate, i.e. reciprocal of reliability, measured over 30-day window under +/-20% power supply variations, was ~ 1.5% +/- 1%. We then utilize multiple instances of the basic block to demonstrate physically unclonable functional primitive with 10-bit hidden challenge generation that encodes more than 10^19 challenge response pairs and has comparable uniformity, diffusiveness, and bit error rate.

Motivation & Objective

• To develop a physically unclonable function (PUF) primitive that leverages intrinsic hardware variations for strong security in interconnected systems.
• To utilize the stochastic behavior of memristive devices to generate unique, unpredictable cryptographic responses.
• To demonstrate high uniformity, diffusiveness, and reliability in a dense, reconfigurable architecture suitable for hardware security.
• To scale the basic PUF block into a larger functional primitive with hidden challenge generation and massive CRP space.

Proposed method

• Design and fabrication of a 3D passive metal-oxide memristive crossbar array with a 10×10 250-nm half-pitch layout.
• Exploitation of process-induced variations in nonlinear I-V characteristics of crosspoint memristors as a source of randomness.
• Implementation of analog conductance tuning to reconfigure the PUF state and enable reusability.
• Use of multiple stacked 2-layer crossbar blocks to create a 10-bit hidden challenge generator with high entropy.
• Characterization of security metrics including uniformity, diffusivity, and bit error rate under environmental variations.
• Evaluation of uniqueness by re-tuning conductances within the same crossbar and measuring response divergence.

Experimental results

Research questions

• RQ1 Can memristive crossbar arrays with nonlinear I-V characteristics generate PUF responses with near-ideal uniformity and diffusivity?
• RQ2 To what extent does analog conductance tuning enable reconfigurability while preserving PUF security properties?
• RQ3 How does the system maintain low bit error rate under power supply variations over extended periods?
• RQ4 What is the achievable entropy and challenge-response pair space in a scalable PUF architecture based on stacked memristive crossbars?

Key findings

• The average uniformity and diffusivity of 6,000 sampled 64-bit responses were 50% ± 5%, approaching the ideal theoretical limit.
• Uniqueness of the PUF, measured by re-tuning conductances in the same crossbar, was 50% ± 1%, indicating high response diversity.
• The bit error rate was measured at ~1.5% ± 1% over a 30-day period under ±20% power supply variations, demonstrating high reliability.
• A scalable PUF primitive with 10-bit hidden challenge generation was demonstrated, encoding more than 10^19 unique challenge-response pairs.
• The system maintained consistent security metrics across multiple test samples, confirming robustness and reproducibility.