Hacking Quantum Key Distribution over Space Division Multiplexing System

On the one hand, Quantum key distribution (QKD) offers unparalleled security relying on the principles of quantum mechanics. On the other hand, space division multiplexing (SDM) is recognized as the route toward a capacity upgrade for current core optical communication networks and will progressively permeate into shorter-reach networks. Incorporating QKD into classical networks, with SDM being one of its components, will enhance data communication security. Understanding the security implications of implementing QKD over SDM is crucial for the practical deployment of quantum-secure communication technologies, especially in scenarios where high data capacity and multiplexing techniques are essential. In this paper, we study a QKD eavesdropping use case where connectivity is provided via SDM fibers. Specifically, we discuss the detector blinding attack (DBA) concerning inter-core crosstalk in an entanglement based QKD system. Additionally, we analyze the blinding power of DBA over quasi-homogeneous and heterogeneous seven-core fiber scenarios. Furthermore, the potential countermeasures to mitigate the impact of such attacks are discussed.