Challenges of Routing in Quantum Key Distribution Networks with Trusted Nodes for Key Relaying

Quantum key distribution (QKD) protocols generate a common secret key at two nodes at different locations. Such a key is used to encryp t and decrypt messages for unconditionally secure communications through a classical channel. Originally, QKD protocols were designed to work between two nodes directly connected through a point-to-point quantum channel. Currently, commercial QKD systems have limited range and key rate. To increase key rate and extend range, the key generated by QKD at one end node is relayed hop-by-hop to the other end node through multiple trusted nodes. In a QKD network with multiple pairs of communicating nodes, routing deals with deciding for each pair which trusted nodes are used to form a path connecting the end nodes. This article presents an overview of QKD, and highlights the differences between QKD routing and classical routing. The challenges of QKD routing are presented. Existing works dealing with the challenges are surveyed. This article ends with a discussion on remaining research issues.