On the “Cracking” Scheme in the Paper “A Directional Coupler Attack Against the Kish Key Distribution System” by Gunn, Allison and Abbott

Abstract

Recently, Gunn, Allison and Abbott (GAA) [http://arxiv.org/pdf/1402.2709v2.pdf] proposed a new scheme to utilize electromagnetic waves for eavesdropping on the Kirchhoff-law-Johnson-noise (KLJN) secure key distribution. We proved in a former paper [Fluct. Noise Lett. 13 (2014) 1450016] that GAA's mathematical model is unphysical. Here we analyze GAA's cracking scheme and show that, in the case of a loss-free cable, it provides less eavesdropping information than in the earlier (Bergou)-Scheuer-Yariv mean-square-based attack [Kish LB, Scheuer J, Phys. Lett. A 374:2140-2142 (2010)], while it offers no information in the case of a lossy cable. We also investigate GAA's claim to be experimentally capable of distinguishing-using statistics over a few correlation times only-the distributions of two Gaussian noises with a relative variance difference of less than 10 -8. Normally such distinctions would require hundreds of millions of correlations times to be observable. We identify several potential experimental artifacts as results of poor KLJN design, which can lead to GAA's assertions: deterministic currents due to spurious harmonic components caused by ground loops, DC offset, aliasing, non-Gaussian features including non-linearities and other non-idealities in generators, and the timederivative nature of GAA's scheme which tends to enhance all of these artifacts.

A directional wave measurement attack against the Kish key distribution system

“…It was suggested by Chen et al25 that mains interference or DC offsets, might be responsible for our results, as they would produce an apparent DC offset during each measurement. Note that DC offsets are removed by high-pass filtering after digitisation, as shown in Figure 7, and 50 Hz interference is suppressed as well.…”

“…The magnitude of the 50 Hz interference measured on the V x channel—see Figure 6—is 15 mV RMS after amplification, and remains constant whether or not a complete circuit exists through the two resistors to ground, thus suggesting this effect to be insignificant on that channel. Interference picked up by the V channel—the quantity considered by Chen et al25—increases with the establishment of a current loop, but at 40 μV RMS this is more than 85 dB below the generator signal, and so insignificant in the short time over which we average.…”

A Static-loop-current Attack Against the Kirchhoff-Law-Johnson-Noise (KLJN) Secure Key Exchange System

“…This potential information leak was pointed out in [53] as the potential source of information leak in the case of significant cable resistance. However, it has not been realized in [53] that information leak can exist even at zero cable resistance.…”

Comments on “A New Transient Attack on the Kish Key Distribution System”

“…The present paper concerns the classical statistical-physicsbased Kirchhoff-law-Johnson-noise (KLJN) key distribution system, delineated in Figure 1, which is no exception to the tradition of the research area, and the creation of the KLJN schemes [3,4] immediately triggered attacks [5][6][7]. The various attacks [5][6][7][8][9][10][11][12][13][14][15][16] have led to useful discussions [17][18][19][20][21][22][23], including corrections of flaws in the attacks [19][20][21][22][23] and developments of new defense protocols [5,10,11,13,24,25] as well as protocols that have increased immunity against attacks in general [24][25][26][27]. Furthermore, KLJN schemes that are totally immune to a certain attack have been presented [13,[28][29][30] as has a new system that is immune to all existing attacks [31].…”

“…Furthermore, KLJN schemes that are totally immune to a certain attack have been presented [13,[28][29][30] as has a new system that is immune to all existing attacks [31]. Responses to the attacks have included plain denials of their validity [18,[21][22][23], and in some cases experimental results that purportedly supported an attack have been found flawed [23]. The debates sometimes represent a standoff between opposing parties with different scientific backgrounds, which is a typical feature of science debates on breakthrough results in physics, as observed already by Max Planck [32].…”