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

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.Comment: 11 pages, 6 Figures, and Journal pape

Véletlenszerű fluktuációk analízisén és hasznosításán alapuló mérési és titkosítási eljárások vizsgálata

Random signals - "noises" - aren’t necessarily hindrances to be eliminated, they can carry information about the examined system. They can also play a constructive role - optimal functioning of some systems are made only possible by appropriate noise application. In the dissertation results are presented in areas which are examples of utilising noises in a constructive role or as an information source. The subject of the first half of the thesis is the analysis of the Kirchhoff-Law-Johnson-Noise (KLJN) secure key exchange protocol. First, the necessary and sufficient conditions of noise properties for unconditional security are deducted using the tools of mathematical statistics only, giving a mathematical proof for the system's perfect security. Next, the generalization of the protocol is presented, allowing the two communicating parties to use different hardware, i.e. resistors with different values. This result not only makes the practical application of the protocol much easier, but resulted in the reinterpretation of the classical physical description of the original KLJN protocol’s security . Finally the supplement of the generalized protocol is presented, in which the components previously bringing non-ideality and information leakage into the system became a part of the unconditionally secure ideal system, which is evidently a big step forward for the protocol's practical applications. Thereafter a new field of application for using fluctuations as an information source is shown. The presented results about analyzing kayak paddlers' motion signals pointed out that the quality of the paddling is correlated to the fluctuation of the period and stroke impulse, which characterise the period of the motion. Thus the temporal indicators characterizing the period fluctuations and the spectral indicators based on the raw motion signals' signal-to-noise ratio could contain extra information. The latter method of spectral variability analysis could be useful for other periodic signals as well

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