[Paper Review] Cable Capacitance Attack against the KLJN Secure Key Exchange

Hsien-Pu Chen, Elias Gonzalez+2 more|viXra|Aug 11, 2015

Advanced Statistical Modeling Techniques56 references4 citations

TL;DR

This paper investigates the impact of parasitic cable capacitance on the security of the KLJN key exchange system, demonstrating through LTSPICE simulations that capacitance introduces a measurable information leak. The study shows that privacy amplification and capacitor killer techniques effectively eliminate the leak, preserving unconditional security in practical implementations.

ABSTRACT

The security of the Kirchhoff-law-Johnson-(like)-noise (KLJN) key exchange system is based on the Fluctuation-Dissipation-Theorem of classical statistical physics. Similarly to quantum key distribution, in practical situations, due to the non-idealities of the building elements, there is a small information leak, which can be mitigated by privacy amplification or other techniques so that the unconditional (information theoretic) security is preserved. In this paper, the industrial cable and circuit simulator LTSPICE is used to validate the information leak due to one of the non-idealities in KLJN, the parasitic (cable) capacitance. Simulation results show that privacy amplification and/or capacitor killer (capacitance compensation) arrangements can effectively eliminate the leak.

Motivation & Objective

• To analyze the security implications of parasitic cable capacitance in the KLJN key exchange system.
• To evaluate the extent of information leakage caused by non-idealities in real-world implementations.
• To test the effectiveness of privacy amplification and capacitor killer techniques in mitigating capacitance-induced leaks.
• To validate the theoretical security of KLJN under practical circuit imperfections using LTSPICE simulations.

Proposed method

• The authors use the LTSPICE circuit simulator to model real-world cable characteristics, including parasitic capacitance.
• Simulations are conducted on a standard KLJN key exchange setup with realistic component non-idealities.
• The information leak is quantified by analyzing voltage and current traces over time to detect signal correlation.
• Privacy amplification is applied to the leaked data to assess its effectiveness in removing exploitable information.
• A capacitor killer circuit is implemented to compensate for parasitic capacitance and reduce signal distortion.
• Security metrics are evaluated based on the residual information after mitigation techniques.

Experimental results

Research questions

• RQ1 To what extent does parasitic cable capacitance introduce an information leak in the KLJN key exchange?
• RQ2 Can privacy amplification effectively remove the information leak caused by cable capacitance?
• RQ3 How effective is the capacitor killer technique in compensating for capacitance-induced signal leakage?
• RQ4 Does the combination of privacy amplification and capacitance compensation restore unconditional security in practical KLJN systems?

Key findings

• Parasitic cable capacitance introduces a measurable information leak in the KLJN key exchange system, as confirmed by LTSPICE simulations.
• The information leak is detectable through voltage and current trace analysis, indicating a potential side-channel vulnerability.
• Privacy amplification effectively reduces the leaked information to negligible levels, preserving unconditional security.
• The capacitor killer technique successfully compensates for parasitic capacitance, minimizing signal distortion and leakage.
• The combined use of privacy amplification and capacitor killer eliminates the security threat posed by cable capacitance.
• The results confirm that practical KLJN systems can maintain information-theoretic security when these mitigation techniques are applied.