Abstract
Most polarization-based BB84 quantum key distribution (QKD) systems utilize multiple lasers to generate one of four polarization quantum states randomly. However, random bit generation with multiple lasers can potentially open critical side channels that significantly endangers the security of QKD systems. In this paper, we show unnoticed side channels of temporal disparity and intensity fluctuation, which possibly exist in the operation of multiple semiconductor laser diodes. Experimental results show that the side channels can enormously degrade security performance of QKD systems. An important system issue for the improvement of quantum bit error rate (QBER) related with laser driving condition is further addressed with experimental results.
Highlights
Trials of secure information transfer between two distant parties have driven the development of the field of quantum key distribution (QKD) whose security is guaranteed by the nature of quantum physics
We discussed critical side channel effects possibly occurred in random bit generation with multiple semiconductor laser diodes, which are temporal disparity and intensity fluctuation among photon pulses
We showed that the phenomena are severe under low DC bias condition, which allows an eavesdropper to obtain correlations between consecutive pulses from the same laser diode
Summary
Trials of secure information transfer between two distant parties have driven the development of the field of quantum key distribution (QKD) whose security is guaranteed by the nature of quantum physics. Many unnoticed degree of freedoms, so called side channels, usually open loopholes for eavesdroppers, which degrades the performance of secret key exchanges [1,2,3,4,5]. In most polarization-based QKD systems, Alice randomly turns on one of four semiconductor laser diodes for each time slot to generate one of four polarization quantum states. In [3], physical quantities such as spatial, temporal, and spectral characteristics which are possibly different among multiple laser diodes were discussed, which need to be identical to avoid information leakage. Intensity fluctuation of a single semiconductor laser diode was reported in periodic pulse generation with a single laser for phase-encoding QKD system [5]
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