The Wiretap Channel for Capacitive PUF-Based Security Enclosures

TL;DR

This paper develops a wiretap channel model using q-ary polar codes to enhance the security of capacitive PUF-based enclosures, ensuring tamper detection without compromising noise correction.

Contribution

It introduces a novel wiretap channel implementation for PUF security enclosures using q-ary polar codes, balancing error correction and tamper sensitivity.

Findings

Achieves 100 bits of physical layer security for 306 bits of entropy.

Models PUF response behavior under external influences.

Demonstrates the effectiveness of the error correction scheme via Monte Carlo simulation.

Abstract

In order to protect devices from physical manipulations, protective security enclosures were developed. However, these battery-backed solutions come with a reduced lifetime, and have to be actively and continuously monitored. In order to overcome these drawbacks, batteryless capacitive enclosures based on Physical Unclonable Functions (PUFs) have been developed that generate a key-encryption-key (KEK) for decryption of the key chain. In order to reproduce the PUF-key reliably and to compensate the effect of noise and environmental influences, the key generation includes error correction codes. However, drilling attacks that aim at partially destroying the enclosure also alter the PUF-response and are subjected to the same error correction procedures. Correcting attack effects, however, is highly undesirable as it would destroy the security concept of the enclosure. In general, designing error correction codes such that they provide tamper-sensitivity to attacks, while still correcting noise and environmental effects is a challenging task. We tackle this problem by first analyzing the behavior of the PUF-response under external influences and different post-processing parameters. From this, we derive a system model of the PUF-based enclosure, and construct a wiretap channel implementation from q-ary polar codes. We verify the obtained error correction scheme in a Monte Carlo simulation and demonstrate that our wiretap channel implementation achieves a physical layer security of 100 bits for 306 bits of entropy for the PUF-secret. Through this, we further develop capacitive PUF-based security enclosures and bring them one step closer to their commercial deployment.