S-CAD: Selective Classical Advantage Distillation for Quantum Conference Key Agreement

TL;DR

This paper introduces S-CAD, a new selective advantage distillation protocol for quantum conference key agreement, with proven security and practical evaluation in network topologies.

Contribution

It generalizes prior QCKA+CAD work by enabling selective application of CAD and provides an asymptotic security proof against coherent attacks.

Findings

S-CAD outperforms previous protocols in certain scenarios.

Selective CAD can improve key rates in star network topologies.

Disabling CAD entirely can be optimal in some configurations.

Abstract

Quantum conference key agreement (QCKA) protocols utilize GHZ states to establish shared group keys between multiple parties. While previous work has shown that standard Classical Advantage Distillation (CAD) protocols can sometimes benefit QCKA performance, it was unknown if past results were asymptotically tight. In this work, we design a new CAD protocol, "Selective Classical Advantage Distillation (S-CAD)", for QCKA, which generalizes prior QCKA+CAD work and allows the parties to selectively enable or disable CAD. We derive an asymptotic proof of security against general coherent attacks, which outperforms prior work. Finally, we evaluate in a variety of simulated star network topologies, showing when S-CAD can help, and when it is best to disable CAD entirely.