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Security against Trojan-horse attacks on a self-compensating all-fiber polarization modulator

Alberto De Toni1, Aynur Cemre Aka1, Costantino Agnesi1, Davide Giacomo Marangon1, Giuseppe Vallone1,2, and Paolo Villoresi1,2

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Phys. Rev. A 113, 052420 – Published 11 May, 2026

DOI: https://doi.org/10.1103/bgdd-1vl9

Abstract

Quantum key distribution (QKD) leverages the principles of quantum mechanics to exchange a secret key between two parties. Unlike classical cryptographic systems, the security of QKD is not reliant on computational assumptions but is instead rooted in the fundamental laws of physics. In a QKD protocol, any attempt by an eavesdropper to intercept the key is detectable: this provides an unprecedented level of security, making QKD an attractive solution for secure communication in an era increasingly threatened by the advent of quantum computers and their potential to break classical cryptographic systems. However, QKD also faces several practical challenges such as transmission loss and noise in quantum channels, finite key size effects, and implementation flaws in QKD devices. Addressing these issues is crucial for the large-scale deployment of QKD and the realization of a global quantum Internet. A whole body of research is dedicated to the hacking of the quantum state source, for example using Trojan-horse attacks (THAs), where the eavesdropper injects light into the system and analyzes the back-reflected signal. In this paper, we study the vulnerabilities against THAs of the iPOGNAC encoder, first introduced in [M. Avesani et al., Opt. Lett. 45, 4706 (2020)], to propose adapted countermeasures that can mitigate such attacks.

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Phys. Rev. A 113, 052420– Published 11 May, 2026
  • Received 24 October 2025
  • Accepted 22 April 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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