Attacks and countermeasures against electromagnetic field information leakage from quantum cryptography networks

Nowadays, quantum key distribution (QKD) has gradually moved from the laboratory to practical applications. However, the inherent imperfections of practical QKD devices would cause side channels. Among them, there is one critical side channel vulnerability that is often overlooked, i.e., information leakage of the electromagnetic field (LEMF). In this work, we carry out systematic investigations on the LEMF by utilizing a practical phase-coding BB84 QKD system as an example. We demonstrate that LEMF from the widely used modulators could be exploited by a malicious eavesdropper to obtain corresponding encoding information assisted with artificial intelligence algorithms, posing a serious threat for practical QKD systems. To solve this problem, we conduct security analysis on LEMF and build a mathematical model on the final secure key rate. Moreover, we give out corresponding countermeasures to reduce information leakage and thus enhance practical security of QKD systems. Therefore, our current work can provide important theoretical and experimental foundations for the future development of secure large-scale quantum communication networks.