Detecting Practical Attacks for Continuous-Variable Quantum Key Distribution Using Quantum k-Nearest Neighbor

Continuous-variablequantum key distribution (CVQKD) enables information-theoretically secure communications between two legitimate users. However, practical CVQKD systems remain vulnerable to various attacks, while existing machine-learning-based detection schemes suffer from increasing computational complexity when processing large-scale monitoring data. In this paper, we propose a quantum k-nearest neighbor (QkNN)-based multiclass attack detection framework for CVQKD systems. Specifically, physical features extracted from Bob’s monitoring data are encoded into quantum states and subsequently classified using the QkNN algorithm to identify different attack behaviors. Furthermore, by incorporating the attack ratio, retained-data ratio, and attack detection performance into secret key rate analysis, an attack-aware secret key rate model is established to characterize the influence of practical attacks on key generation. Simulation results demonstrate that the proposed scheme achieves high attack classification accuracy while significantly reducing computational complexity. Moreover, the proposed framework establishes a direct connection between attack detection and secret key generation, enabling a more realistic security evaluation for practical CVQKD systems.