Upper bounds for Trojan-horse attack key leakage in QKD systems

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Upper bounds for Trojan-horse attack key leakage in QKD systems
Sushchev I.S.1,2*, Bulavkin D.S.1, Bugai K.E.1,3, Sidelnikova A.S.1,2, Zyzykin A.P.1, Dvoretskiy D.A.1,3
1SFB Laboratory, Ltd, Moscow, 127273, Russia
2Quantum Technology Centre and Faculty of Physics, M. V. Lomonosov Moscow State University, Moscow, 119991, Russia
3Bauman Moscow State Technical University, 2nd Baumanskaya str. 5-1, Moscow, Russia 107005
*corresponding author e-mail: [email protected]
INTRODUCTION
Quantum key distribution (QKD) provides two legitimate users (Alice and Bob) with an absolute secure key. This level of security is ensured by the laws of quantum
mechanics. The key remains secure as long as the implementation of the QKD system satisfy specific requirements. Any discrepancy in physical characteristics of the
components can lead to the information leakage to an eavesdropper (Eve). A side channel of information leakage found in QKD systems is the backflash emission from
InGaAs single-photon avalanche photodiodes (SPAD). That is so-called the backflash attack.
In recent decades, active studies of the properties of backflash emission have been carried out. The dependencies of the backflash intensity on the quantum efficiency of the
SPAD, the temperature, the SPAD gate widths and the mean photon number per pulse of the stimulating emission were obtained previously \cite{bib2,bib3}. The backflash
spectrum was also measured in \cite{bib4}. In this paper, the dependency of the probability of the backflash on the stimulating laser's wavelength is investigated. A noticeable
deviation of the backflash probability from the average value in a certain spectral range of the stimulating emission can either lead to a loophole in the QKD system for Eve or
the opportunity to reduce information leakage through this side channel selecting the communication wavelength.
Weak coherent pulses (WCPs)
Model assumptions: Eve utilizes
coherent states (faint laser pulses)
Phase coding
Polarization coding
Coherent state