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arXiv:2207.05675 · Fluctuation and Noise Letters

Time Synchronization Protocol for the KLJN Secure Key Exchange Scheme

László B. Kish

Published Jun 9, 2022• 6 citations
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Abstract

The information theoretically secure Kirchhoff-law-Johnson-noise (KLJN) key exchange scheme, similarly to quantum key distribution (QKD), is also potentially vulnerable against clock attacks, where Eve takes over the control of clock synchronization in the channel. This short note aims to introduce a time synchronization protocol scheme for Alice and Bob, which is resistant against arbitrary time delay attacks, both symmetric and asymmetric ones. We propose and explore various ways of clock synchronization for the KLJN system and propose an ultimate protocol that preserves time and hardware integrity under arbitrary attacks.

DOI
10.1142/s0219477522500468

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The information theoretically secure Kirchhoff-law-Johnson-noise (KLJN) key exchange scheme, similarly to quantum key distribution (QKD), is also potentially vulnerable against clock attacks, where Eve takes over the control of clock synchronization in the channel. This short note aims to introduce a time synchronization protocol scheme for Alice and Bob, which is resistant against arbitrary time delay attacks, both symmetric and asymmetric ones. We propose and explore various ways of clock synchronization for the KLJN system and propose an ultimate protocol that preserves time and hardware integrity under arbitrary attacks.
We demonstrate the security vulnerability of an ideal Kirchhoff–Law–Johnson–Noise key exchanger against transient attacks. Transients start when Alice and Bob connect a wire to their chosen resistor at the beginning of each clock cycle. A transient attack takes place during a short duration of time, before the transients reflected from the end of Alice and Bob mix together. The information leak arises from the fact that Eve (the eavesdropper) monitors the cable and analyzes the transients during this time period. We will demonstrate such a transient attack, and then, we introduce a defense protocol to protect against the attack. Computer simulations demonstrate that after applying the defense method the information leak becomes negligible.
We demonstrate the security vulnerability of the ideal Kirchhoff-Law-Johnson-Noise (KLJN) key exchanger against transient attacks. Transients start when Alice and Bob connect the wire to their chosen resistor at the beginning of each clock cycle. A transient attack takes place during a short duration of time, before the transients reflected from the end of Alice and Bob mix together. The information leak arises from the fact that Eve (the eavesdropper) monitors the cable, and analyzes the transients during this time period. We will demonstrate such a transient attack, and, then we introduce a defense protocol to protect against the attack. Computer simulations demonstrate that after applying the defense method the information leak becomes negligible.
This paper introduces and demonstrates two new attacks against the Kirchhoff-Law-Johnson-Noise (KLJN) secure key exchange scheme. The attacks are based on random number generators with compromised security. First we explore the situation in which Eve knows the seed of both Alice's and Bob's random number generators. We show that in this situation Eve can crack the secure key bit within a fraction of the bit exchange period even if her current and voltage measurements have only a single bit of resolution. In the second attack, we explore the situation in which Eve knows the seed of only Alice's random number generator. We show that in this situation Eve can still crack the secure key bit but she needs to use the whole bit exchange period for the attack. The security of the KLJN key exchange scheme, similarly to other protocols, necessitates that the random number generator outputs are truly random for Eve.
This paper introduces and demonstrates four new statistical attacks against the Kirchhoff-Law-Johnson-Noise (KLJN) secure key exchange scheme. The attacks utilize compromised random number generators (RNGs) at Alice’s/Bob’s site(s). The case of partial correlations between Alice’s/Bob’s and Eve’s probing noises is explored, that is, Eve’s knowledge of Alice’s and Bob’s noises is limited but not zero. We explore the bilateral situation where Eve has partial knowledge of Alice’s and Bob’s RNGs. It is shown that in this situation Eve can crack the secure key bit by taking the highest cross-correlation between her probing noises and the measured voltage noise in the wire. She can also crack the secure key bit by taking the highest cross-correlation between her noise voltages and her evaluation of Alice’s/Bob’s noise voltages. We then explore the unilateral situation in which Eve has partial knowledge of only Alice’s RNG thus only those noises (of Alice and Eve) are correlated. In this situation, Eve can still crack the secure key bit, but for sufficiently low error probability, she needs to use the whole bit exchange period for the attack. The security of the KLJN key exchange scheme, similarly to other protocols, necessitates that the RNG outputs are truly random for Eve.
This paper demonstrates the vulnerability of the Kirchhoff-Law-Johnson-Noise (KLJN) secure key exchanger to compromised random number generator(s) even if these random numbers are used solely to generate the noises emulating the Johnson noise of Alice’s and Bob’s resistors. The attacks shown are deterministic in the sense that Eve’s knowledge of Alice’s and/or Bob’s random numbers is basically deterministic. Moreover, no statistical evaluation is needed, except for rarely occurring events of negligible, random waiting time and verification time. We explore two situations. In the first case, Eve knows both Alice’s and Bob’s random noises. We show that, in this situation, Eve can quickly crack the secure key bit by using Ohm’s Law. In the other situation, Eve knows only Bob’s random noise. Then Eve first can learn Bob’s resistance value by using Ohm’s Law. Therefore, she will have the same knowledge as Bob, thus at the end of the bit exchange period, she will know Alice’s bit.
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.