Relaxing Trust Assumptions on Quantum Key Distribution Networks

Quantum security over long distances with untrusted relays is largely unfounded and is still an open question for active research. Nevertheless, quantum networks based on trusted relays are being built across the globe. However, standard QKD network architecture implores a complete trust requirement on QKD relays, which is too demanding and limits the use cases for QKD networks. In this work, we explore the possibility to securely relay a secret in a QKD network by relaxing the trust assumptions (if not completely) on the relay. We characterize QKD relays with different trust levels, namely, Full Access Trust (FAT), Partial Access Trust (PAT), and No Access Trust (NAT). As the name suggests, each level defines the degree with which a relay is required to be trusted with the secret provided by the key management system for end-to-end communication. We then review and propose multiple constructions of the QKD key management system based on the different trust levels. Main contribution of the paper is realized by evaluating key management systems with no access trust level. In principle, we review key management with centralized topology and propose a new decentralized key management system. These different topologies provide various advantages based on the QKD network requirements, allowing an operational flexibility in the architecture. We believe this work presents a new perspective to the open problem of providing a confiding and a practical solution for future long range secure communications