Upper bounds on the performance of differential-phase-shift quantum key distribution

TL;DR

This paper establishes tighter upper bounds on the security of differential-phase-shift quantum key distribution by analyzing sequential attacks based on optimal unambiguous phase discrimination, highlighting fundamental limitations.

Contribution

It introduces a new analysis of sequential attacks using optimal unambiguous discrimination, providing improved security bounds for DPS QKD protocols.

Findings

Sequential attacks can impose stricter security limits on DPS QKD.

Optimal unambiguous discrimination enhances attack effectiveness.

Tighter upper bounds inform the security thresholds of the protocol.

Abstract

In this paper, we investigate limitations imposed by sequential attacks on the performance of a differential-phase-shift (DPS) quantum key distribution (QKD) protocol with weak coherent pulses. Specifically, we analyze a sequential attack based on optimal unambiguous discrimination of the relative phases between consecutive signal states emitted by the source. We show that this attack can provide tighter upper bounds for the security of a DPS QKD scheme than those derived from sequential attacks where the eavesdropper aims to identify the state of each signal emitted by the source unambiguously.