Routing With Minimum Activated Trusted Nodes in Quantum Key Distribution Networks for Secure Communications

Cyber-physical systems rely heavily on communication networks for remote monitoring and control. It is crucial to protect the communication networks from cyberattacks because an attack on the physical subsystem can be indirectly launched from a compromised cyber subsystem. Since remote control devices have limited computational power, we ensure communication confidentiality and integrity using one-time-pad (OTP) symmetric cryptography, which despite simple is unconditionally secure. To provide OTP with secret keys, we use quantum key distribution (QKD) across multiple hops, where each intermediate relay is a trusted node. These nodes can be weak points in cyberattacks. Hence, this article focuses on routing in multihop QKD networks that reduces the required number of trusted nodes. We formulate and solve an optimization problem to find the set of QKD routes that minimizes the number of activated trusted nodes while satisfying the secret key rate requirements of multiple communicating pairs. Extensive evaluation results confirm that the proposed scheme can indeed has fewer activated trusted nodes as compared to a benchmark scheme that finds only the shortest paths for communicating pairs.