Chun-Yan Li

Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all the detection attacks, thus when it is combined with the decoy state method, the final key is unconditional security, even the practical weak coherent source are used by Alice and Bob. However, until now, the analysis of decoy state MDI-QKD with weak coherent state is incomplete. In this paper, we derive, with only vacuum+weak decoy state, some tight formulas to estimate the lower bound of yield and the upper bound of error rate for the fraction of signals in which both Alice and Bob send single photon pulse to the untrusted third party Charlie. The numerical simulations show that our method with only vacuum+weak decoy state can asymptotically approach to the theoretical limit of the infinite number of decoy states. Furthermore, the statistical fluctuation due to the finite length of date is also considered based on the standard statistical analysis.

Since a single photon source is not available for practical quantum key distribution (QKD) systems nowadays, weak coherent state are widely used in practical systems which suffers from the photon-number-splitting (PNS) attack. Fortunately, the decoy state method is proposed to defeat it, in which there is an important assumption that the signal state and decoy state is not distinguishable for Eve. However, in practical systems, this assumption is invalid in some situations, then the security of decoy state method will be compromised. Actually, a wavelength-selected PNS (WSPNS) is proposed by our group to break the security of decoy state “plug-and-play” QKD systems by exploiting the imperfection of the intensity modulator (IM) that used to generate the signal state and decoy state. Our analysis shows that Eve can use our attack to determinately distinguish the signal state and decoy state, then the security of decoy state method is broken.