Thermal blinding of gated detectors in quantum cryptography

TL;DR

This paper reveals that thermal effects can blind and control detectors in quantum cryptography systems, enabling undetectable eavesdropping by heating avalanche photodiodes with bright illumination.

Contribution

It introduces thermal blinding as a new method to compromise quantum key distribution detectors, expanding understanding of vulnerabilities in practical QKD systems.

Findings

Thermal blinding can be achieved by heating avalanche photodiodes with bright illumination.

Detectors can be triggered after thermal blinding using short bright pulses.

Thermal inertia allows pre-blinding in systems with transmission pauses.

Abstract

It has previously been shown that the gated detectors of two commercially available quantum key distribution (QKD) systems are blindable and controllable by an eavesdropper using continuous-wave illumination and short bright trigger pulses, manipulating voltages in the circuit [L. Lydersen et al., Nat. Photonics DOI:10.1038/nphoton.2010.214]. This allows for an attack eavesdropping the full raw and secret key without increasing the quantum bit error rate (QBER). Here we show how thermal effects in detectors under bright illumination can lead to the same outcome. We demonstrate that the detectors in a commercial QKD system Clavis2 can be blinded by heating the avalanche photo diodes (APDs) using bright illumination, so-called thermal blinding. Further, the detectors can be triggered using short bright pulses once they are blind. For systems with pauses between packet transmission such as the plug-and-play systems, thermal inertia enables Eve to apply the bright blinding illumination before eavesdropping, making her more difficult to catch.