Quantum key distribution with an efficient countermeasure against correlated intensity fluctuations in optical pulses

Ken-Ichiro Yoshino,Toshihiko Sasaki,Mikio Fujiwara,Masahide Sasaki,Akio Tajima,Kensuke Nakata,Masahiro Takeoka,Tatsuya Sumiya,Masato Koashi,Akihisa Tomita

doi:10.1038/s41534-017-0057-8

Abstract

Quantum key distribution (QKD) allows two distant parties to share secret keys with the proven security even in the presence of an eavesdropper with unbounded computational power. Recently, GHz-clock decoy QKD systems have been realized by employing ultrafast optical communication devices. However, security loopholes of high-speed systems have not been fully explored yet. Here we point out a security loophole at the transmitter of the GHz-clock QKD, which is a common problem in high-speed QKD systems using practical band-width limited devices. We experimentally observe the inter-pulse intensity correlation and modulation pattern-dependent intensity deviation in a practical high-speed QKD system. Such correlation violates the assumption of most security theories. We also provide its countermeasure which does not require significant changes of hardware and can generate keys secure over 100 km fiber transmission. Our countermeasure is simple, effective and applicable to wide range of high-speed QKD systems, and thus paves the way to realize ultrafast and security-certified commercial QKD systems.

Highlights

Quantum key distribution (QKD)[1,2,3] allows two legitimate parties, Alice and Bob, to establish symmetric keys with the proven security even in the presence of an eavesdropper, Eve, who has unbounded computational power
It implies that the first half of the modulation signals has little effect on the modulation signals to the intensity modulator (IM) is controlled by fiber length second half
Almost all the influence of pattern connected in front of the IM with the accuracy of 50 ps effect are limited to the adjacent pulses

Summary

Introduction

Quantum key distribution (QKD)[1,2,3] allows two legitimate parties, Alice and Bob, to establish symmetric keys with the proven security even in the presence of an eavesdropper, Eve, who has unbounded computational power Thanks to this unique feature, referred to as “information theoretic security”, QKD, combined with Vernam’s one-time pad cipher, enables the everlasting protection of confidentiality of data transmission, and must be an essential element to construct a long-term security system which cannot be realized only by cryptographic schemes based on computational security. By employing the ultrafast optical communication devices, high-speed QKD systems stably operated at GHzclock frequency is realized in the installed fiber networks.[13,14,15]

Methods

Results

Conclusion