On the Robustness of (Photonic) Quantum Key Distribution with Classical Alice

TL;DR

This paper demonstrates that Quantum Key Distribution protocols involving classical Alice remain robust even when practical issues like photon losses and multi-photon states are considered, extending previous idealized robustness results.

Contribution

It proves the robustness of QKD with classical Alice under realistic conditions involving photon losses and multi-photon states, which was not established before.

Findings

QKD with classical Alice is robust against photon losses.

Robustness holds even with multi-photon states.

Extends idealized robustness results to practical scenarios.

Abstract

Quantum Key Distribution (QKD) with classical Bob has recently been suggested and proven robust. Following this work, QKD with classical Alice was also suggested and proven robust. The above protocols are ideal in the sense that they make use of qubits. However, in the past, well-known QKD protocols that were proven robust and even proven unconditionally secure, when qubits are used, were found to be totally insecure when photons are used. This is due to sensitivity to photon losses (e.g., Bennett's two-state protocol) or sensitivity to losses combined with multi-photon states (e.g., the photon-number-splitting attack on the weak-pulse Bennett-Brassard protocol, BB84). Here we prove that QKD with classical Alice is still robust when photon losses and even multi-photon states are taken into account.