Secure Decentralized Key Relaying via Random Walks in Dynamic Semi-Trusted QKD Networks

Abstract

Due to distance and key-rate limitations, current quantum key distribution (QKD) technology requires the use of trusted nodes, which, together with QKD links, form a graph referred to as a QKD network. We address the problem of securely routing (relaying) keys between trusted nodes, where some of them can be malicious.

Existing solutions typically rely on centralized controllers, which simplify adaptive routing and congestion control but introduce single points of failure. Moreover, some proactive key-relay protocols distribute keys to multiple nodes in the network; thus, compromising a single node results in the compromise of the shared keys.

In this paper, we propose a decentralized, topology-oblivious key-relay algorithm based on random walks. Our algorithm provides information-theoretic security (ITS) for QKD network topologies having at least one non-malicious path between any pair of nodes (in particular, $k$-vertex-disjoint paths can tolerate malicious cartels of size $k-1$). Besides, it provides strong computational security guarantees for other topologies (even for graphs with malicious articulation points).

We evaluate the proposed algorithm on the GÉANT GN4-3N topology, which provides a realistic approximation of a multi-state cross-border topology for future QKD networks.