Security of biased BB84 quantum key distribution with finite resource * Zhao Liang-Yuan(赵良圆) a)b) , Li Hong-Wei(李宏伟) a)b)c) † , Yin Zhen-Qiang(银振强) a)b) ‡ , Chen Wei(陈 巍) a)b) , You Juan(尤 娟) a) , and Han Zheng-Fu(韩正甫) a)b) a)

Quantum coin tossing (QCT) is an important primitive of quantum cryptography and has received continuous interest. However, in practical QCT, Bob's detectors can be subjected to detector-side channel attacks launched by dishonest Alice, which will possibly make the protocol completely insecure. Here, we report a simple strategy of a detector-blinding attack based on a recent experiment. To remove all the detector side-channels, we present a solution of measurement-device-independent QCT (MDI-QCT). This method is similar to the idea of MDI quantum key distribution (QKD). MDI-QCT is loss-tolerant with single-photon sources and has the same bias as the original losstolerant QCT under a coherent attack. Moreover, it provides the potential advantage of doubling the secure distance for some special case. Finally, MDI-QCT can also be modified to fit the weak coherent state sources. Thus, based on the rapid development of practical MDI-QKD, our proposal can be implemented easily.

Quantum private queries (QPQ) is an important cryptography protocol aiming to protect both the user’s and database’s privacy when the database is queried privately. Recently, a variety of practical QPQ protocols based on quantum key distribution (QKD) have been proposed. However, for QKD-based QPQ the user’s imperfect detectors can be subjected to some detector- side-channel attacks launched by the dishonest owner of the database. Here, we present a simple example that shows how the detector-blinding attack can damage the security of QKD-based QPQ completely. To remove all the known and unknown detector side channels, we propose a solution of measurement-device-independent QPQ (MDI-QPQ) with single- photon sources. The security of the proposed protocol has been analyzed under some typical attacks. Moreover, we prove that its security is completely loss independent. The results show that practical QPQ will remain the same degree of privacy as before even with seriously uncharacterized detectors.

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