Improved Semi-Quantum Key Distribution with Two Almost-Classical Users

TL;DR

This paper enhances a mediated semi-quantum key distribution protocol, increasing its efficiency and noise tolerance, and analyzes its performance under various channel conditions, making quantum secure communication more practical for classical users.

Contribution

The paper extends a mediated SQKD protocol to improve efficiency and noise resilience, with detailed key-rate analysis and performance evaluation in noisy channels.

Findings

Improved key-rate in asymptotic attack scenarios

Enhanced noise tolerance and efficiency

Effective performance in lossy and noisy channels

Abstract

Semi-quantum key distribution (SQKD) protocols attempt to establish a shared secret key between users, secure against computationally unbounded adversaries. Unlike standard quantum key distribution protocols, SQKD protocols contain at least one user who is limited in their quantum abilities and is almost "classical" in nature. In this paper, we revisit a mediated semi-quantum key distribution protocol, introduced by Massa et al., in 2019, where users need only the ability to detect a qubit, or reflect a qubit; they do not need to perform any other basis measurement; nor do they need to prepare quantum signals. Users require the services of a quantum server which may be controlled by the adversary. In this paper, we show how this protocol may be extended to improve its efficiency and also its noise tolerance. We discuss an extension which allows more communication rounds to be directly usable; we analyze the key-rate of this extension in the asymptotic scenario for a particular class of attacks and compare with prior work. Finally, we evaluate the protocol's performance in a variety of lossy and noisy channels.