Semi-quantum cryptography

Zhang Wei, Daowen Qiu, Paulo Mateus

Semi-quantum key distribution (SQKD) can share secret keys by using less quantum resource than its fully quantum counterparts, and this likely makes SQKD become more practical and realizable. In this paper, we present a new SQKD protocol by introducing the idea of B92 protocol in fully quantum cryptography into SQKD. In this protocol, the sender Alice just sends one quantum state to the classical Bob and Bob just prepares a fixed state in the preparation process. It is much simpler than the existing SQKD and potentially much easier to be implemented. It can be seen as a semi-quantum version of B92 protocol, compared to the protocol BKM07 as the semi-quantum version of BB84 in fully quantum cryptography. We verify that it is more efficient than the existing single-state SQKD protocols by introducing an efficiency parameter. Specifically, we prove it is secure against a restricted collective attack by computing a lower bound of the key rate in the asymptotic scenario. Then we can find a threshold value of errors such that for all error rates less than this value, the secure key can be definitely established between the legitimate users definitely. We make an illustration of how to compute the threshold value in case the reverse channel is a depolarizing one with parameter [Formula: see text]. Though the threshold value is a little smaller than those of some existing SQKD protocols, it can be comparable to the B92 protocol in fully quantum cryptography.

Gan Gao, Yue Wang, Xueying Cui +1 more

Recently, Jiang et al. proposed a quantum cryptography protocol [Mod. Phys. Lett. B 32 (2018) 1850125] which can implement the equal exchange of secret information between the two parties with the help of semi-trusted third party. Here, it will be shown that the protocol is insecure and has the drawback of information leakage.

Takeshi Koshiba

Subhendu Bera

Julia Guskind, Walter O. Krawec

Semi-quantum cryptography involves at least one user who is semi-quantum or “classical” in nature. Such a user can only interact with the quantum channel in a very restricted way. Many semi-quantum key distribution protocols have been developed, some with rigorous proofs of security. Here we show for the first time that quantum random number generation is possible in the semi-quantum setting. We also develop a rigorous proof of security, deriving a bound on the random bit generation rate of the protocol as a function of noise in the channel. Our protocol and proof may be broadly applicable to other quantum and semi-quantum cryptographic scenarios where users are limited in their capabilities.