Composable Security Analysis for Passive Continuous-Variable Quantum Key Distribution Using Multimode Thermal Source.

Passive continuous variable quantum key distribution using multimode thermal source waives the necessity of usage of amplitude and phase modulators, thus it can effectively simplify the implementation of quantum key distribution. Compared with Gaussian modulation quantum key distribution scheme, this protocol is more cost-effective. However, the composable security of this scheme under collective attack has not been proved. In view of this, we take the composable security of the protocol under collective attack into consideration, and analyze the impact of the average photon number and mode-overlap coefficient on the performance of passive continuous variable quantum key distribution using multimode thermal source. In order to make comparison, we also calculate the asymptotic secret key rate of the passive continuous variable quantum key distribution protocol using multimode thermal source. Simulation results show that the composable secret key rate of this protocol is always lower than its asymptotic secret key rate. When the number of exchanged optical pulse signals is large enough, the composable secret key rate of the protocol approaches the asymptotic secret key rate. In addition, the composable secret key rate of this scheme can be further improved with the increase of average output photon number and mode-overlap coefficient. [ABSTRACT FROM AUTHOR]