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National Conference on Communications

Differential Phase Encoding Scheme for Measurement-Device-Independent Quantum Key Distribution

Shashank Kumar Ranu, Anil Prabhakar, Prabha Mandayam

Published Feb 1, 2019• 1 citation
Publisher

Abstract

This paper proposes a measurement-device-independent quantum key distribution (MDI-QKD) scheme based on differential phase encoding. The differential phase shift MDI-QKD (DPS-MDI-QKD) couples the advantages of DPS-QKD with that of MDI-QKD. The proposed scheme offers resistance against photon number splitting attack and phase fluctuations as well as immunity against detector side-channel vulnerabilities. The design proposed in this paper uses weak coherent pulses in a superposition of three orthogonal states, corresponding to one of three distinct paths in a delay-line interferometer. The classical bit information is encoded in the phase difference between pulses traversing successive paths. This 3-pulse superposition offers enhanced security compared to using a train of pulses by decreasing the learning rate of an eavesdropper and unmasking her presence with an increased error rate upon application of intercept and resend attack and beamsplitter attack. The proposed scheme employs phase locking of the sources of the two trusted parties so as to maintain the coherence between their optical signal, and uses a beamsplitter (BS) at the untrusted node (Charlie) to extract the key information from the phase encoded signals.

DOI
10.1109/ncc.2019.8732260

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This paper proposes a measurement-device-independent quantum key distribution (MDI-QKD) scheme based on differential phase encoding. The differential phase shift MDI-QKD (DPS-MDI-QKD) couples the advantages of DPS-QKD with that of MDI-QKD. The proposed scheme offers resistance against photon number splitting attack and phase fluctuations as well as immunity against detector side-channel vulnerabilities. The design proposed in this paper uses weak coherent pulses in a superposition of three orthogonal states, corresponding to one of three distinct paths in a delay-line interferometer. The classical bit information is encoded in the phase difference between pulses traversing successive paths. This 3-pulse superposition offers enhanced security compared to using a train of pulses by decreasing the learning rate of an eavesdropper and unmasking her presence with an increased error rate upon application of intercept and resend attack and beamsplitter attack. The proposed scheme employs phase locking of the sources of the two trusted parties so as to maintain the coherence between their optical signal, and uses a beamsplitter (BS) at the untrusted node (Charlie) to extract the key information from the phase encoded signals.
Measurement-device-independent quantum key distribution (MDI-QKD) can be immune to all detector side-channel attacks and guarantee the information-theoretical security even with uncharacterized single photon detectors. MDI-QKD has been demonstrated in both laboratories and field-tests by using attenuated lasers combined with the decoy-state technique. However, it is a critical assumption that the sources used by legitimate participants are trusted in MDI-QKD. Hence, it is possible that a potential security risk exists. Here we propose a new scheme of polarization-encoding-based MDI-QKD with a single untrusted source, by which the complexity of the synchronization system can be reduced and the success rate of the Bell-state measurement can be improved. Meanwhile, the decoy-state method is employed to avoid the security issues introduced by a non-ideal single photon source. We also derive a security analysis of the proposed system. In addition, it seems to be a promising candidate for the implementation for QKD network in the near future.
The ideal measurement-device-independent quantum key distribution (MDI-QKD), which is immune to all detector side-channel attacks, is built on the Bell state measurement of two single-photon states. However, in practical MDI-QKD where phase-randomized weak coherent pulses (PR-WCPs) are used, the mismatch between states preparation and measurement in X basis leads to the bit error rate of more than 25%, which poses a challenge to the security of QKD. In this paper, we provide a security analysis of practical MDI-QKD based on polarization coding. We analyze the Hong-Ou-Mandel interference of PR-WCPs and Poisson-distributed photon number states (PNs), and find that these two sources are equivalent in MDI-QKD. The security analysis based on entanglement distillation is carried out on PNs, and the measurement results in Z basis and X basis are averaged to overcome the noncorrelation of the error rates in these two bases. Compared with GLLP scheme, a tighter key rate is obtained in this work, and the key rate deviates from the linear key rate bound in a short distance due to the finite proportion of multiphoton terms.
Measurement-Device-Independent Quantum Key Distribution (MDI-QKD) enhances security by removing vulnerabilities associated with detector side channels. Real-world implementations of measurement device independent (MDI) QKD face practical challenges such as channel asymmetry and physical imperfections, which degrade the visibility of Hong-Ou-Mandel (HOM) interference, an essential factor in determining the secure key rate. In this work, we evaluate the performance of differential phase encoded (DPE) MDI-QKD under realistic, asymmetric conditions. We analyse the effects of polarisation and pulse-width mismatches caused by channel asymmetry and identify tolerable limits for secure key generation. We introduce a plug-and-play DPE-MDI-QKD architecture that mitigates polarisation fluctuations using Faraday mirrors and also compensates for pulse-width mismatches. Furthermore, we propose an improved sifting scheme that raises the sifting efficiency from49\frac{4}{9}94​to23\frac{2}{3}32​, improving the secure key generation rates by 50% and making it especially suitable for plug-and-play systems. These results offer practical insights into enhancing the robustness and efficiency of DPE-MDI-QKD, enabling more secure quantum communication over imperfect and asymmetric quantum channels.
Measurement-device-independent quantum key distribution (MDI-QKD) protocol was proposed to remove all the detector side channel attacks, while its security relies on the trusted encoding systems. Here we propose a one-sided MDI-QKD (1SMDI-QKD) protocol, which enjoys detection loophole-free advantage, and at the same time weakens the state preparation assumption in MDI-QKD. The 1SMDI-QKD can be regarded as a modified MDI-QKD, in which Bob's encoding system is trusted, while Alice's is uncharacterized. For the practical implementation, we also provide a scheme by utilizing coherent light source with an analytical two decoy state estimation method. Simulation with realistic experimental parameters shows that the protocol has a promising performance, and thus can be applied to practical QKD applications.
In this paper, a phase-encoded measurement device independent quantum key distribution (MDI-QKD) protocol without a shared reference frame is presented, which can generate secure keys between two parties while the quantum channel or interferometer introduces an unknown and slowly time-varying phase. The corresponding secret key rate and single photons bit error rate is analysed, respectively, with single photons source (SPS) and weak coherent source (WCS), taking finite-key analysis into account. The numerical simulations show that the modified phase-encoded MDI-QKD protocol has apparent superiority both in maximal secure transmission distance and key generation rate while possessing the improved robustness and practical security in the high-speed case. Moreover, the rejection of the frame-calibrating part will intrinsically reduce the consumption of resources as well as the potential security flaws of practical MDI-QKD systems.
Abstract Realistic quantum key distribution (QKD) systems suffer from side-channel attacks, which manipulate single-photon detectors. Although measurement-device-independent QKD schemes were proposed to free QKD parties (Alice and Bob) from such measurement devices, these schemes are not easy to be implemented in practice because they require precise synchronization between signals from distant parties. On the other hand, differential phase shift (DPS) QKD is a simple system for practical implementation with current optical equipment. In this study, we propose a simple modification in DPS QKD to prevent side-channel attacks (control blinding and controlling attacks) such that Bob randomly attenuates the incoming signal. This modification allows Bob to utilize photon statistics during attenuated time slots in DPS-QKD systems, using which the side-channel attacks are revealed.