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Metrology and Measurement Systems

The problem of information leak due to parasitic loop currents and voltages in the KLJN secure key exchange scheme

Mutaz Y. Melhem, László B. Kish

Published Jan 15, 2019• 18 citations
Publisher

Abstract

The Kirchhoff-law-Johnson-noise (KLJN) secure key exchange scheme offers unconditional security, however it can approach the perfect security limit only in the case when the practical system's parameters approach the ideal behavior of its core circuitry.In the case of non-ideal features, non-zero information leak is present.The study of such leaks is important for a proper design of practical KLJN systems and their privacy amplifications in order to eliminate these problems.

DOI
10.24425/mms.2019.126335

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The Kirchhoff-law-Johnson-noise (KLJN) secure key exchange scheme offers unconditional security, however it can approach the perfect security limit only in the case when the practical system's parameters approach the ideal behavior of its core circuitry.In the case of non-ideal features, non-zero information leak is present.The study of such leaks is important for a proper design of practical KLJN systems and their privacy amplifications in order to eliminate these problems.
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 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.
The Kirchhoff-law-Johnson-noise (KLJN) scheme is a statistical/physical secure key exchange system based on the laws of classical statistical physics to provide unconditional security. We used the LTSPICE industrial cable and circuit simulator to emulate one of the major active (invasive) attacks, the current injection attack, against the ideal and a practical KLJN system, respectively. We show that two security enhancement techniques, namely, the instantaneous voltage/current comparison method, and a simple privacy amplification scheme, independently and effectively eliminate the information leak and successfully preserve the system’s unconditional security.
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 ([Formula: see text]) at the second order ([Formula: see text]), third order ([Formula: see text]) and a combination of the second and third orders ([Formula: see text]) on the security of the KLJN scheme. It is demonstrated that 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.
Abstract The Kirchhoff-law-Johnson-noise (KLJN) scheme is a statistical/physical secure key exchange system based on the laws of classical statistical physics to provide unconditional security. We used the LTSPICE industrial cable and circuit simulator to emulate one of the major active (invasive) attacks, the current injection attack, against the ideal and a practical KLJN system, respectively. We show that two security enhancement techniques, namely, the instantaneous voltage/current comparison method, and a simple privacy amplification scheme, independently and effectively eliminate the information leak and successfully preserve the system’s unconditional security.
In this study, a new attack against the Kirchhoff-Law-Johnson-Noise (KLJN) key distribution system is explored. The attack is based on utilizing a parasitic voltage-source in the loop. Relevant situations often exist in the low-frequency limit in practical systems, especially when the communication is over a distance, or between different units within an instrument, due to a ground loop and/or electromagnetic interference (EMI). Our present study investigates the DC ground loop situation when no AC or EMI effects are present. Surprisingly, the usual current/voltage comparison-based defense method that exposes active attacks or parasitic features (such as wire resistance allowing information leaks) does not function here. The attack is successfully demonstrated and proposed defense methods against the attack are shown.
The Kirchhoff-Law-Johnson-(like)-Noise (KLJN) key exchange system is a promising low-cost alternative to the quantum key distribution and is based solely on the laws of classical physics. Although several papers have been published in the field, there is still an ongoing debate about the security of the method. In our paper we will give an overview the most important findings about the security of the KLJN system and show the effects of the non-idealities of the system on the information leak. We will also analyze different methods of proposed cracking the KLJN protocol, including the latest directional coupler attack.