Device Calibration Impacts Security of Quantum Key Distribution

Nitin Jain,Vadim Makarov,Dominique Elser,Christoffer Wittmann,Carlos Wiechers,Lars Lydersen,Christoph Marquardt,Gerd Leuchs

doi:10.1103/physrevlett.107.110501

Abstract

Characterizing the physical channel and calibrating the cryptosystem hardware are prerequisites for establishing a quantum channel for quantum key distribution (QKD). Moreover, an inappropriately implemented calibration routine can open a fatal security loophole. We propose and experimentally demonstrate a method to induce a large temporal detector efficiency mismatch in a commercial QKD system by deceiving a channel length calibration routine. We then devise an optimal and realistic strategy using faked states to break the security of the cryptosystem. A fix for this loophole is also suggested.

Highlights

Quantum key distribution (QKD) offers unconditionally secure communication as eavesdropping disturbs the transmitted quantum states, which in principle leads to the discovery of the eavesdropper Eve [1]
We propose and experimentally demonstrate a method to induce a large temporal detector efficiency mismatch in a commercial quantum key distribution (QKD) system by deceiving a channel length calibration routine
The establishment of the quantum channel remains an implicit assumption in security proofs: channel characterization and calibration of the cryptosystem hardware, especially the steps involving two-party communication, haven’t yet been taken into account

Summary

Device calibration impacts security of quantum key distribution

Characterizing the physical channel and calibrating the cryptosystem hardware are prerequisites for establishing a quantum channel for quantum key distribution (QKD). Quantum key distribution (QKD) offers unconditionally secure communication as eavesdropping disturbs the transmitted quantum states, which in principle leads to the discovery of the eavesdropper Eve [1]. Eve targets imperfections of avalanche photodiode (APD) based single-photon detectors [13] that allow her to control them remotely. Another important aspect of QKD security not yet investigated, is the calibration of the devices. The establishment of the quantum channel remains an implicit assumption in security proofs: channel characterization (e.g. channel length) and calibration of the cryptosystem hardware, especially the steps involving two-party communication, haven’t yet been taken into account. The calibration of the QKD devices must be carefully implemented, otherwise it is prone to hacks that may strengthen existing, or create new eavesdropping opportunities for Eve

BS φAlice

PM voltage

Eve stays below

Findings

DLs output controller electronic tap on classical detector