On the "cracking" scheme in the paper "A directional coupler attack against the Kish key distribution system" by Gunn, Allison and Abbott

TL;DR

This paper critically analyzes GAA's electromagnetic eavesdropping scheme on the KLJN system, showing it offers limited or no information under ideal conditions and identifying experimental artifacts that could falsely suggest security breaches.

Contribution

It demonstrates the unphysical nature of GAA's model, compares its eavesdropping effectiveness with previous attacks, and highlights potential experimental artifacts affecting security claims.

Findings

GAA's scheme provides less information than previous attacks in loss-free cables.

GAA's scheme offers no information in lossy cables.

Experimental artifacts can mimic eavesdropping signals, affecting security assessments.

Abstract

Recently, Gunn, Allison and Abbott (GAA) [http://arxiv.org/pdf/1402.2709v2.pdf] proposed a new scheme to utilize electromagnetic waves for eavesdropping on the Kirchhoff-law-Johnson-noise (KLJN) secure key distribution. We proved in a former paper [Fluct. Noise Lett. 13 (2014) 1450016] that GAA's mathematical model is unphysical. Here we analyze GAA's cracking scheme and show that, in the case of a loss-free cable, it provides less eavesdropping information than in the earlier (Bergou)-Scheuer-Yariv mean-square-based attack [Kish LB, Scheuer J, Phys. Lett. A 374 (2010) 2140-2142], while it offers no information in the case of a lossy cable. We also investigate GAA's claim to be experimentally capable of distinguishing - using statistics over a few correlation times only - the distributions of two Gaussian noises with a relative variance difference of less than 10^-8. Normally such distinctions would require hundreds of millions of correlations times to be observable. We identify several potential experimental artifacts as results of poor KLJN design, which can lead to GAA's assertions: deterministic currents due to spurious harmonic components caused by ground loops, DC offset, aliasing, non-Gaussian features including non-linearities and other non-idealities in generators, and the time-derivative nature of GAA's scheme which tends to enhance all of these artifacts.