Hacking the Quantum Key Distribution System by Exploiting the Avalanche-Transition Region of Single-Photon Detectors

Abstract

As necessary steps toward practical and secure quantum key distribution (QKD), identifying and patching possible attacks are important and valuable. This study discusses an avalanche-transition-region (ATR) attack on a gated-mode avalanche photodiode (APD) detector, widely used in QKD systems. Unlike other attacks, this one leaves almost no trace; the eavesdropper introduces less than 0.5% quantum bit-error rate, and the photocurrent and afterpulse probability before and after hacking are nearly identical. These findings highlight the importance of detection signals in real-life QKD systems, and are crucial to enhancing the security of practical QKD.