Dynamic-threshold-based pre-relaying for enhanced key allocation in quantum-secured networks

Quantum key distribution (QKD) is experiencing a rapid increase of interest due to its security advantages in the face of quantum computers. However, typical QKD deployments are point-to-point and limited in terms of distance, which significantly restricts their utilization for end-user applications. To overcome these restrictions, trusted relays are adopted as intermediate nodes to allow the transition to QKD networks (QKDNs), where one of the hallmarks is the key management system. In this work, we investigate different key allocation strategies as a method to enhance the performance of key management systems in QKDN from the perspective of key allocation success rate and key delivery delay. We first describe an upgrade model from classical to QKDN at three distinct network layers—quantum, key management, and service. Then, we propose a novel, to our knowledge, key allocation strategy leveraging the benefits of key storage and relaying as a solution to improve the QKDN performance. To achieve this, our method makes use of end-to-end virtual quantum key pools (VQKPs) implemented between non-adjacent nodes requesting key material. We introduce static and dynamic upper and lower threshold limits at the VQKP level, with the dynamic thresholds adapted according to application demand, to control the key distribution in the network and fill the pools ahead of end-user requests. We demonstrate through simulations that the introduction of thresholds achieves performance enhancement and explain the trade-off between the key allocation success rate and key delivery delay evaluation metrics in comparison with different on-demand key allocation strategies.