Risk Analysis of Countermeasures Against the Trojan-Horse Attacks on Quantum Key Distribution Systems in 1260–1650 nm Spectral Range

The results of investigation of the spectral characteristics of some passive fiber-optic components, such as optical isolators, circulators, spectral filters and multiplexers, used in quantum key distribution (QKD) systems and contributing to the protection of QKD system from active optical probing attacks are presented. An assessment of the required degree of isolation is also given, which ensures reliable protection of the QKD system against Trojan-horse attacks under the most stringent conditions for legitimate users. Based on the formulated requirements and measurement results, the effectiveness of protection using the investigated passive insulating components is analyzed. Using the example of calculating the insulation for the QKD system scheme presented in the work, the achievement of the required level of isolation (150 dB) in the entire considered spectral range is shown.