Routing Strategies for Quantum Key Distribution Networks Based on Trusted Relay Nodes

Quantum key distribution (QKD) networks enable connected parties to exchange cryptographic keys that are information-theoretically secure. In absence of quantum repeaters, key relaying between trusted nodes is the foremost method to overcome fundamental rate-distance limitations of point-to-point QKD links. This method requires consumption of keys generated by each independent QKD link in the relay path, but these resources can be depleted, resulting in failure. Hence, selecting suitable relay paths is essential for enabling successful key exchanges between each pair of communicating parties. This paper presents how the success rate of key relaying can be increased by frequently recomputing relay paths considering the availability of keys, i.e., resource-aware routing. A centralized routing approach is adopted for the key relay process, which is emulated to measure and compare the success rates achieved by different routing algorithms. It was found that using centralized resource-aware routing can increase the success rate up to 13.4 percentage point compared to selecting the shortest path without taking the availability of link keys into account. However, the differences amongst the success rates achieved by different resource-aware routing algorithms are statistically insignificant, if the centralized routing approach described in this paper is used. Therefore, this paper recommends to focus on resource aware routing algorithms that are computationally inexpensive and suitable for large-scale implementation.