Experimental Protocol Fingerprinting in Quantum Networks via Physical Layer Side Channel Analysis

Research Overview

As quantum networks transition from theoretical concepts to practical implementations, they face new security challenges. While quantum protocols are designed to be secure at the logical layer, their physical implementation involves hardware components—such as photon sources, detectors, and optical channels—that may leak information. This paper investigates whether an external observer can identify which quantum communication protocol is currently active by passively monitoring these physical layer signals without directly measuring the encoded quantum states.

The researchers implemented four distinct quantum protocols on a polarization-entangled photon testbed: entanglement distribution, quantum gate sequences, heralded quantum key distribution (QKD), and quantum identity authentication (QIA). To simulate a passive adversary, they introduced a beam splitter to tap a fraction of the optical signal. The observer collected two primary types of data: single-photon detection statistics (via a time-tagger) and optical power measurements. Using these features, the team developed a data-driven classification framework to distinguish between the protocols.

Findings and Security Implications

The study demonstrates that different protocols exhibit unique physical signatures, allowing for successful identification even with minimal signal access. Classification accuracy reached 96% with a 30:70 sampling ratio and remained robust (70–89%) even when the observer only accessed 10% of the signal. Crucially, the researchers used Bell inequality measurements to confirm that this passive tapping does not destroy the entanglement of the primary signal, meaning an adversary could potentially monitor network activity without being detected by the legitimate users. Interpretability analysis revealed that timing features, such as photon arrival rates, were the most significant contributors to the classification success.