Establishing shared secret keys on quantum line networks: protocol and security

TL;DR

This paper demonstrates the security of multi-user quantum key establishment over a line network topology, highlighting advantages like simplified intermediate nodes and direct pairwise key sharing without routing, using the abstract cryptography framework.

Contribution

It introduces a secure protocol for quantum line networks with simplified intermediate nodes, ensuring composable security for multi-user key establishment.

Findings

Security of quantum key establishment on line networks proven.

Intermediate nodes require only single-qubit operations, simplifying hardware.

Security is composable, suitable for encryption and other applications.

Abstract

We show the security of multi-user key establishment on a single line of quantum communication. More precisely, we consider a quantum communication architecture where the qubit generation and measurement happen at the two ends of the line, whilst intermediate parties are limited to single-qubit unitary transforms. This network topology has been previously introduced to implement quantum-assisted secret-sharing protocols for classical data, as well as the key establishment, and secure computing. This architecture has numerous advantages. The intermediate nodes are only using simplified hardware, which makes them easier to implement. Moreover, key establishment between arbitrary pairs of parties in the network does not require key routing through intermediate nodes. This is in contrast with quantum key distribution (QKD) networks for which non-adjacent nodes need intermediate ones to route keys, thereby revealing these keys to intermediate parties and consuming previously established ones to secure the routing process. Our main result is to show the security of key establishment on quantum line networks. We show the security using the framework of abstract cryptography. This immediately makes the security composable, showing that the keys can be used for encryption or other tasks.