Security of a practical quantum secure direct communication system under weak-randomness basis selection attack

Quantum secure direct communication (QSDC) enables the user to directly transmit secret messages through quantum channels without pre-shared keys. However, the imperfection of devices brings a security loophole to QSDC. The weak-random basis selection attack is a strong attack mode, where the eavesdropper can manipulate users' basis selection probability distribution, and thus reduce the error rate caused by her eavesdropping. In this paper, we propose the first, to the best of our knowledge, general quantitative security analysis model for the practical QSDC system under the weak-randomness basis selection attack. We characterize the imperfect basis selection by the parameter ε. The simulation results show that when ε increases from 0 to 0.1, the maximal secure communication distance reduces from 34 km to 24 km. When ε> 0.32, the maximal secure communication distance reduces to 0. Our work indicates the importance of inspecting the QSDC system's security loopholes from the weak-randomness basis selection attack and contributes to enhancing its practical security under real experimental conditions.