Current Injection Attack against the KLJN Secure Key Exchange

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

Johnson(-like)-Noise-Kirchhoff-Loop Based Secure Classical Communicator Characteristics, for Ranges of Two to Two Thousand Kilometers, via Model-Line

A pair of Kirchhoff-Loop-Johnson(-like)-Noise communicators, which is able to work over variable ranges, was designed and built. Tests have been carried out on a model-line performance characteristics were obtained for ranges beyond the ranges of any known direct quantum communication channel and they indicate unrivalled signal fidelity and security performance of the exchanged raw key bits. This simple device has single-wire secure key generation and sharing rates of 0.1, 1, 10, and 100 bit/second for corresponding copper wire diameters/ranges of 21 mm / 2000 km, 7 mm / 200 km, 2.3 mm / 20 km, and 0.7 mm / 2 km, respectively and it performs with 0.02% raw-bit error rate (99.98 % fidelity). The raw-bit security of this practical system significantly outperforms raw-bit quantum security. Current injection breaking tests show zero bit eavesdropping ability without triggering the alarm signal, therefore no multiple measurements are needed to build an error statistics to detect the eavesdropping as in quantum communication. Wire resistance based breaking tests of Bergou-Scheuer-Yariv type give an upper limit of eavesdropped raw bit ratio of 0.19 % and this limit is inversely proportional to the sixth power of cable diameter. Hao's breaking method yields zero (below measurement resolution) eavesdropping information.Comment: Featured in New Scientist, Jason Palmer, May 23, 2007. http://www.ece.tamu.edu/%7Enoise/news_files/KLJN_New_Scientist.pdf Corresponding Plenary Talk at the 4th International Symposium on Fluctuation and Noise, Florence, Italy (May 23, 2007

The Impact of Parasitic DC And AC Sources on the Security of the KLJN Secure Key Exchange Scheme

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. This dissertation contains four interrelated studies of the security of the KLJN system. In the first study, a new attack against the 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). The 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 based information leaks) does not workhere. The attack is successfully demonstrated and we proposed defense methods against the attack are shown. The second study investigates the security of the KLJN key distribution system with unknown parasitic DC-voltage sources at both Alice’s and Bob’s ends. This work is the generalization of our earlier investigation with a single-end parasitic source. Similarly to the first study, the defense method based on comparing current/voltage data at Alice's and Bob's ends is useless here since the wire currents and voltages are equal at both ends. 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. Some defense methods against the attack are shown. The third study addresses a new question regarding the security of the KLJN scheme compromised by DC sources at Alice and Bob: What is the impact of these parasitic sources on active attacks, such as the man-in-the-middle (MITM) attack, or the current injection attack? The surprising answer is that the parasitic DC sources actually increase the security of the system because, in the case of the MITM attack, they make it easier to uncover the eavesdropping. In some of the cases Eve can fix this deficiency but then the problem gets reduced to the original MITM attack to which the KLJN scheme is immune, as it is already proven earlier. In the last section a new attack against the KLJN secure key exchange scheme is introduced. The attack exploits a parasitic/periodic AC voltage-source at either Alice’s or Bob’s end. Such situations exist due to AC ground loops and electromagnetic interference (EMI). In the low-frequency limit, the procedure is the generalized form of the former DC ground loop-based attack. In the high-frequency case, the spectrum of the wire voltage is utilized. The attack is demonstrated in both the low and the high-frequency situations. Defense protocols against the attack are also discussed

KLJN Statistical Physical Secure Key Exchange System: Attacks and Defense

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. This dissertation contains three main studies of the KLJN system. The first study presents the refutation of a physical model, proposed by Gunn, Allison and Abbott (GAA), to utilize electromagnetic waves for eavesdropping on the KLJN secure key distribution. The correct mathematical model of the GAA scheme is deduced, which is based on impedances at the quasi-static limit. Mathematical analysis and simulation results confirm our approach and prove that GAA’s experimental interpretation is incorrect too. The second study analyzes one of the passive (listening) attacks against the KLJN system, the cable capacitance attack. 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. 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 third study explores one of the major active (invasive) attacks, the current injection attack. The LTSPICE is used to emulate the attack against the ideal and a practical KLJN system, respectively. It is shown 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

Transient Attacks against the VMG-KLJN Secure Key Exchanger

The security vulnerability of the Vadai, Mingesz, and Gingl (VMG) Kirchhoff-Law-Johnson-Noise (KLJN) key exchanger, as presented in the publication "Nature, Science Report 5 (2015) 13653," has been exposed to transient attacks. Recently an effective defense protocol was introduced (Appl. Phys. Lett. 122 (2023) 143503) to counteract mean-square voltage-based (or mean-square current-based) transient attacks targeted at the ideal KLJN framework. In the present study, this same mitigation methodology has been employed to fortify the security of the VMG-KLJN key exchanger. It is worth noting that the protective measures need to be separately implemented for the HL and LH scenarios. This conceptual framework is corroborated through computer simulations, demonstrating that the application of this defensive technique substantially mitigates information leakage to a point of insignificance