Electromagnetic Side-Channel Vulnerability in QKD Equipment

Abstract

Although the unconditional security of quantum key distribution (QKD) protocol has been mathematically proven, actual QKD network nodes may be vulnerable to side-channel attacks such as ElectroMagnetic (EM) wave leakage. In this study, we measured EM emissions from a prototype QKD device implementing a time-bin decoy BB84 protocol with Y- and Z- basis. We measured the EM spectra and waveforms at distances of 0 m and 3 m from the transmitter and receiver inside an anechoic chamber. The results showed that the transmitter was the primary source of EM wave leakage, and distinct differences were observed between the generated quantum states (Y0, Y1, Z0, Z1) at the third harmonic of the 1241.6 MHz system clock. Furthermore, stronger EM signals were observed for the Z basis than for the Y basis. These state-dependent EM signals suggest a vulnerability to side-channel attacks that extract qubit information from the EM wave leakage. On the other hand, closing the EM-shielding rack resulted in an average attenuation of 21.2dB (ranging from 12.7 to 36.6dB), demonstrating that EM wave leakage other than clock-frequency components can be effectively suppressed to below −100 dBm. The findings of this study indicate that side-channel risks exist in QKD devices, but they can be reduced through appropriate EM shielding and device design. This study provides important guidelines for establishing security standards for trusted nodes in practical QKD networks.