Generalized DC loop current attack against the KLJN secure key exchange scheme

TL;DR

This paper introduces a generalized attack on the KLJN secure key exchange system exploiting parasitic DC sources, analyzes its effectiveness, and proposes defense strategies, highlighting vulnerabilities in existing security assumptions.

Contribution

It generalizes previous single-source attacks to multiple parasitic sources and evaluates effective defense mechanisms against this new threat.

Findings

The attack can successfully compromise the KLJN system with unknown parasitic DC sources.

Simple current/voltage comparison defenses are ineffective against this attack.

In situ system simulation-based defenses remain effective against the generalized attack.

Abstract

A new attack against the Kirchhoff Law Johnson Noise (KLJN) secure key distribution system is studied with unknown parasitic DC voltage sources at both Alices and Bobs ends. This paper is the generalization of our earlier investigation with a single end parasitic source. Under the assumption that Eve does not know the values of the parasitic sources, a new attack, utilizing the current generated by the parasitic dc voltage sources, is introduced. The attack is mathematically analyzed and demonstrated by computer simulations. Simple defense methods against the attack are shown. The earlier defense method based solely on the comparison of current/voltage data at Alice's and Bob's terminals is useless here since the wire currents and voltages are equal at both ends. However, the more expensive version of the earlier defense method, which is based on in situ system simulation and comparison with measurements, works efficiently.