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Physical Review Applied

Finite-key security analysis against the Trojan-horse attack on practical reference-frame-independent measurement-device-independent quantum key distribution

Yang Zhou, Hua-Jian Ding, Jing-Yang Liu, Chunhui Zhang, Xing-Yu Zhou, Qin Wang

Published Feb 4, 2025• 3 citations
Publisher

Abstract

Reference-frame-independent measurement-device-independent quantum key distribution (RFI MDI QKD) can resist side-channel attacks against detectors and slow variations of reference frames, thus presenting an advantageous approach for long-distance secure quantum communication. Nevertheless, if an eavesdropper implements a Trojan-horse attack (THA) by injecting bright light into sources, the back-reflected light may carry encoding information into the channel, thereby causing serious information leakage. In this paper, we theoretically evaluate the finite-key security of decoy-state RFI MDI QKD against a THA by employing the reference-state technique and a particular concentration inequality. Additionally, dual-parameter optimization and multibasis-estimation strategies are introduced to reduce statistical fluctuations effectively. Our work demonstrates that RFI MDI QKD can maintain a better performance even in the presence of large reference-frame drifts and a THA, representing a key advancement in strengthening the security of quantum communication in real-world implementations.

DOI
10.1103/physrevapplied.23.024007

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Reference-frame-independent measurement-device-independent quantum key distribution (RFI MDI QKD) can resist side-channel attacks against detectors and slow variations of reference frames, thus presenting an advantageous approach for long-distance secure quantum communication. Nevertheless, if an eavesdropper implements a Trojan-horse attack (THA) by injecting bright light into sources, the back-reflected light may carry encoding information into the channel, thereby causing serious information leakage. In this paper, we theoretically evaluate the finite-key security of decoy-state RFI MDI QKD against a THA by employing the reference-state technique and a particular concentration inequality. Additionally, dual-parameter optimization and multibasis-estimation strategies are introduced to reduce statistical fluctuations effectively. Our work demonstrates that RFI MDI QKD can maintain a better performance even in the presence of large reference-frame drifts and a THA, representing a key advancement in strengthening the security of quantum communication in real-world implementations.
Measurement-device-independent quantum key distribution (MDI QKD) is a promising method for remote key sharing that can eliminate all detector side-channel attacks. However, current security proofs often overlook the potential information leakages from the legitimate users' devices. In a quantum version of Trojan-horse attack (THA), a malicious eavesdropper can inject bright light into the sources of a MDI QKD system and then analyze the back-reflected light to obtain their setting choices, thereby compromising the final security. Here, we derive the finite-key security bounds of decoy-state MDI QKD in the presence of THA, which significantly outperform previous analyses in terms of the secret-key rate and transmission distance. Specifically, we analyze a symmetric three-intensity decoy-state MDI QKD protocol and an efficient four-intensity decoy-state MDI QKD protocol. Our results represent a fundamental step in guaranteeing the implementation security of quantum communication systems.
Reference-frame-independent measurement-device-independent quantum key distribution (RFI-MDI-QKD) is a novel protocol that eliminates all possible attacks on the detector side and the necessity of reference-frame alignment in source sides. However, its performance may degrade notably due to statistical fluctuations since more parameters, e.g., yields and error rates for mismatched-basis events, must be accumulated to monitor the security. In this work, we find that the original decoy states method estimates these yields overpessimistically since it ignores the potential relations between different bases. Through jointly processing parameters of different bases, the performance of RFI-MDI-QKD is greatly improved in terms of the secret key rate and achievable distance when statistical fluctuations are considered (the statistical fluctuation analysis is the first step to the final analysis of the finite key size effect). Our results pave an avenue towards practical RFI-MDI-QKD.
Reference-frame-independent measurement-device-independent quantum key distribution (RFI-MDI-QKD) is proposed to remove all possible detector side channel attacks without the alignment of reference frames. Due to unavoidable multiphoton events in practical sources, the decoy-state method is always adopted in real-life QKD systems. Unlike original MDI-QKD (O-MDI-QKD), the characterization on practical decoy-state RFI-MDI-QKD is still absent to date. In this paper, we investigate the performance of practical decoy-state RFI-MDI-QKD at different misalignments of reference frames with full parameter optimization when considering statistical fluctuations, and provide a clear comparison between decoy-state RFI-MDI-QKD and O-MDI-QKD. Simulation results demonstrate that decoy-state RFI-MDI-QKD can exhibit performance comparable to that of O-MDI-QKD in practical scenarios, which is very robust in QKD systems.
Abstract Most security proofs of quantum key distribution (QKD) disregard the effect of information leakage from the users’ devices, and, thus, do not protect against Trojan-horse attacks (THAs). In a THA, the eavesdropper injects strong light into the QKD apparatuses, and then analyzes the back-reflected light to learn information about their internal setting choices. Only a few recent works consider this security threat, but predict a rather poor performance of QKD unless the devices are strongly isolated from the channel. Here, we derive finite-key security bounds for decoy-state-based QKD schemes in the presence of THAs, which significantly outperform previous analyses. Our results constitute an important step forward to closing the existing gap between theory and practice in QKD.
Abstract Reference-frame-independent measurement-device-independent QKD (RFI-MDI-QKD), immune to both the slow unknown drift of reference frames and detector side channel attacks, can generate information-theoretic secure keys. Despite its natural resistance to the slow drift of reference frames, the performance of practical RFI-MDI-QKD systems descends with the increasing drift of reference frames. In this paper, we demonstrate the worst relative rotation of reference frames for practical RFI-MDI-QKD systems, and investigate their performance against the worst-case scenario, both of which are unclear to date. Simulation results show that, practical RFI-MDI-QKD systems can achieve quite good performance even against the worst-case scenario, which clearly demonstrates that it is possible to implement practical MDI-QKD systems with freely drifting reference frames.
Reference-frame-independent (RFI) measurement-device-independent (MDI) quantum key distribution (QKD) is immune to all detector side-channel attacks and is insensitive to slow drifts of reference frames; thus, it is a promising candidate for the realization of long-distance quantum secure communications. However, its practical performance is predominantly limited by the finite-data-size effect compared with standard MDI QKD. By combining the collective constraint and joint-study strategy with our parameter estimation processes for the RFI-MDI-QKD protocol, we reduce the influence of the finite-data-size effect and substantially improve the protocol's performance under realistic experimental conditions. Furthermore, a proof-of-principle experimental demonstration is conducted, and a transmission distance of up to 200 km is achieved. Therefore, this study represents a further step toward long-distance quantum secure communications.