Experimental demonstration of phase-remapping attack in a practical quantum key distribution system

TL;DR

This paper experimentally demonstrates a phase-remapping attack on a practical quantum key distribution system, exploiting a security loophole due to imperfect state preparation, resulting in a successful intercept-and-resend attack with a quantum bit error rate below the secure threshold.

Contribution

The study provides the first experimental demonstration of a phase-remapping attack on a commercial QKD system, highlighting a critical security loophole in practical implementations.

Findings

Successfully performed a phase-remapping attack with 19.7% QBER

Attack exploited state preparation errors in a commercial QKD system

QBER remained below the 20% security threshold for BB84

Abstract

Unconditional security proofs of various quantum key distribution (QKD) protocols are built on idealized assumptions. One key assumption is: the sender (Alice) can prepare the required quantum states without errors. However, such an assumption may be violated in a practical QKD system. In this paper, we experimentally demonstrate a technically feasible "intercept-and-resend" attack that exploits such a security loophole in a commercial "plug & play" QKD system. The resulting quantum bit error rate is 19.7%, which is below the proven secure bound of 20.0% for the BB84 protocol. The attack we utilize is the phase-remapping attack (C.-H. F. Fung, et al., Phys. Rev. A, 75, 32314, 2007) proposed by our group.