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arXiv:1806.05596

A Static-Loop-Current Attack against the KLJN Secure Key Exchange System

Mutaz Y. Melhem, László B. Kish

Published Jun 11, 2018• 2 citations

Abstract

A new attack against the Kirchhoff-Law-Johnson-Noise (KLJN) key distribution system is introduced. The attack is based on 1) Utilizing the dc-voltage-source - which we put at Alice’s end in our mathematical modeling of the attack-that could exist due to errors, imbalances, Electromagnetic interference and etc.2) On studying the number of samples per bit in the security key that the measured Alice/Bob voltages exceeds or falls below a threshold voltage, respectively. The threshold voltage is the average between dc voltages across low and high resistors- generated by a dc-voltage source. We count the number of samples the voltage at Bob’s end (containing both the noise and dc components) exceeds the threshold voltage and how many times it falls below the threshold to judge whether the resistor can be guessed as low or high for every cycle. Also for a pre-specified key-length we count the number of high resistance estimations per bit –at Bob’s end-according to the previous criterion and the non-successful estimations per bit to judge the final guessed resistor value at Alice’s end and Bob’s end, where if we have more bits with most of its measured samples are above the threshold voltage then we will predict Bob’s resistance as high resistance, otherwise we predict Bob’s resistance to be low resistance. The Simulation was conducted and the attack proved that it is successful unless the temperature increased dramatically to ranges more than a threshold temperature ~ Kelvin that increases when the number of samples per bit increases.

DOI: 10.20944/preprints201806.0157.v1

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A new attack against the Kirchhoff-Law-Johnson-Noise (KLJN) key distribution system is introduced. The attack is based on 1) Utilizing the dc-voltage-source - which we put at Alice’s end in our mathematical modeling of the attack-that could exist due to errors, imbalances, Electromagnetic interference and etc.2) On studying the number of samples per bit in the security key that the measured Alice/Bob voltages exceeds or falls below a threshold voltage, respectively. The threshold voltage is the average between dc voltages across low and high resistors- generated by a dc-voltage source. We count the number of samples the voltage at Bob’s end (containing both the noise and dc components) exceeds the threshold voltage and how many times it falls below the threshold to judge whether the resistor can be guessed as low or high for every cycle. Also for a pre-specified key-length we count the number of high resistance estimations per bit –at Bob’s end-according to the previous criterion and the non-successful estimations per bit to judge the final guessed resistor value at Alice’s end and Bob’s end, where if we have more bits with most of its measured samples are above the threshold voltage then we will predict Bob’s resistance as high resistance, otherwise we predict Bob’s resistance to be low resistance. The Simulation was conducted and the attack proved that it is successful unless the temperature increased dramatically to ranges more than a threshold temperature ~ Kelvin that increases when the number of samples per bit increases.

A new attack against the Kirchhoff-Law-Johnson-Noise (KLJN) secure key distribution system is studied with unknown parasitic DC-voltage sources at both Alice's and Bob's 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.

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-noise (KLJN) secure key distribution system provides a way of exchanging theoretically secure keys by measuring random voltage and current through the wire connecting two different resistors at Alice's and Bob's ends. Recently new advanced protocols for the KLJN method have been proposed with enhanced performance. In this paper, we analyze the KLJN system and compare with the "intelligent" KLJN (iKLJN) scheme. That task requires determination of the applied resistors and identification of various superpositions of known and unknown noise components. Some statistical tools will be explored to determine how the duration of the bit exchange window (averaging time) influences the performance of the secure bit exchange.

Recently, several passive and active attack methods have been proposed against the Kirchhoff–Law–Johnson–Noise (KLJN) secure key exchange scheme by utilizing direct (DC) loop currents. The DC current attacks are relatively easy, but their practical importance is low. On the other hand, parasitic alternating (AC) currents are virtually omnipresent in wire-based systems. Such situations exist due to AC ground loops and electromagnetic interference (EMI). However, utilizing AC currents for attacks is a harder problem. Here, we introduce and demonstrate AC current attacks in various frequency ranges. The attacks exploit a parasitic/periodic AC voltage-source at either Alice’s or Bob’s end. In the low-frequency case, the procedure is the generalized form of the former DC ground-loop-based attack. In the high-frequency case, the power density 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.

The Kirchhoff-Law-Johnson-Noise (KLJN) secure key distribution system provides a way of exchanging theoretically secure keys by measuring random voltage and current through the wire connecting two different resistors at Alice's and Bob's ends. Recently new advanced protocols for the KLJN method have been proposed with enhanced performance. In this paper we analyze the KLJN system and compare with the intelligent KLJN (iKLJN) scheme. That task requires determination of the applied resistors and identification of various superpositions of known and unknown noise components. Some statistical tools will be explored to determine how the duration of the bit exchange window (averaging time) influences the performance of the secure bit exchange.

The Kirchhoff-Law-Johnson-Noise (KLJN) secure key distribution system provides a way of exchanging information theoretic secure keys by measuring the random voltage and current through the wire connecting two different resistors at Alice's and Bob's ends. Recently new advanced protocols for the KLJN method have been proposed with enhanced performance. In this paper we analyze the KLJN system and compare with “intelligent” KLJN (iKLJN) scheme. This task requires the determination of the applied resistors and the identification of the various superpositions of known and unknown noise components. Some statistical tools to determine how the duration of the bit exchange window (averaging time) influences the performance of secure bit exchange will be explored.