Nonlinearity Attack against the Kirchhoff-Law-Johnson-Noise (KLJN) Secure Key Exchange Protocol

TL;DR

This paper presents a new nonlinear attack on the KLJN secure key exchange protocol, demonstrating how small distortions can cause significant information leaks and proposing methods to mitigate this vulnerability.

Contribution

It introduces a novel attack exploiting noise generator nonlinearity and analyzes how reducing nonlinearity can restore security.

Findings

1% distortion causes notable power flow and information leakage

Reducing wire voltage and temperature decreases nonlinearity

Approaching perfect security by minimizing nonlinearity effects

Abstract

This paper introduces a new attack against the Kirchhoff-Law-Johnson-Noise (KLJN) secure key exchange scheme. The attack is based on the nonlinearity of the noise generators. We explore the effect of total distortion (TD) at the second order (D2), third order (D3), and a combination of the second and third orders (D2,3) on the security of the KLJN scheme. It is demonstrated that a as little as 1% results in a notable power flow along the information channel, which leads to a significant information leak. We also show that decreasing the effective temperature (that is, the wire voltage) and, in this way reducing nonlinearity, results in the KLJN scheme approaching perfect security.