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Physical Review A

Modified general individual attack against differential-phase-shift quantum key distribution

Kyo Inoue, Toshimori Honjo

Published Oct 29, 2024• 4 citations
Publisher

Abstract

Differential-phase-shift (DPS) quantum key distribution (QKD) is a type of QKD protocol. It is a unique QKD scheme wherein a lasting coherent pulse sequence containing numerous photons is transmitted as an information carrier instead of qubits in traditional QKD protocols. Regarding the security of DPS-QKD, a general individual attack (GIA), which first conducts a beam-splitting attack and then entangles probe states with each photon in a pulse sequence after beam splitting, has been presented and is usually assumed to evaluate the DPS-QKD system performance. Thus, this study reconsidered the GIA scheme, examined its feasibility, and consequently modified it to render it feasible. A formula for the secret key creation rate, assuming a modified GIA, was formulated. Calculations using the presented and conventional formulas indicated that while the key creation rates in systems assuming conventional and modified GIAs were approximately the same, the modified GIA resulted in a higher key creation rate in short- and medium-distance systems to a certain extent.

DOI
10.1103/physreva.110.042626

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Differential-phase-shift (DPS) quantum key distribution (QKD) is a type of QKD protocol. It is a unique QKD scheme wherein a lasting coherent pulse sequence containing numerous photons is transmitted as an information carrier instead of qubits in traditional QKD protocols. Regarding the security of DPS-QKD, a general individual attack (GIA), which first conducts a beam-splitting attack and then entangles probe states with each photon in a pulse sequence after beam splitting, has been presented and is usually assumed to evaluate the DPS-QKD system performance. Thus, this study reconsidered the GIA scheme, examined its feasibility, and consequently modified it to render it feasible. A formula for the secret key creation rate, assuming a modified GIA, was formulated. Calculations using the presented and conventional formulas indicated that while the key creation rates in systems assuming conventional and modified GIAs were approximately the same, the modified GIA resulted in a higher key creation rate in short- and medium-distance systems to a certain extent.
A novel type of quantum key distribution (QKD) protocol, called DPS (differential-phase-shift) QKD, was proposed several years ago. A sender transmits a highly-attenuated coherent pulse train with {0, π} phase, and a receiver receives it with a one-bit delay Mach-Zehnder interferometer followed by photon detectors. A secret key is created from photon detection events, whose security is based on the fact that an eavesdropper cannot perfectly measure the phase information of a highly-attenuated coherent pulse train. This protocol has some features of simple setup, potential for a high key creation rate, and robustness against photon-number-splitting attack. This paper overviews DPS-QKD. The operation mechanism is described, and then some experimental efforts are introduced, featuring use of a glass waveguide Mach-Zehnder interferometer and advanced single-photon detectors. The highest key rate and the longest distance have been achieved with the DPS-QKD protocol. Some modified schemes are also presented, including that utilizing quantum entanglement, that using decoy pulses, and that using macroscopic coherent light.
A unique quantum key distribution (QKD) protocol, called DPS (differential-phase-shift) QKD, has been proposed and developed at NTT and Osaka University, which utilizes a coherent pulse train instead of individual photons as in traditional QKD protocols such as BB84. Its security is based on the fact that every phase difference of a highlyattenuated coherent pulse train cannot be fully measured. This protocol has features of simple setup, potential for a high key creation rate, and robustness against photon-number-splitting attack. This paper presents recent research activities on DPS-QKD.
In quantum key distribution (QKD), eavesdropping is generally detected based on bit errors resulting from eavesdropper attacks. This study proposes a QKD scheme for detecting eavesdropping based on the photon-detection rate instead of the bit error rate. The differential-phase-shift (DPS) QKD protocol, which transmits lasting weak coherent pulses, is modified such that decoy pulses with a large mean photon number are randomly inserted into a signal pulse sequence. With this modification, eavesdropping can be detected by monitoring the photon-detection rates at the time slots around the decoy pulses. The key-creation performance of the modified DPS-QKD system is evaluated, and the results indicate that the QKD distance is increased with the modification.
Differential-phase-shift (DPS) quantum key distribution (QKD) is one of the major QKD protocols that can be implemented with a simple setup using a laser source and a passive detection unit. Recently, an information-theoretic security proof of this protocol was established by Mizutani et al. [npj Quantum Inf. 5, 87 (2019)], assuming an infinitely large number of emitted pulses. To implement the DPS protocol in a real-life world, it is indispensable to analyze the security with the finite number of emitted pulses. The extension of the security proof to the finite-size regime requires the accommodation of the statistical fluctuations to determine the amount of privacy amplification. In doing so, Azuma's inequality is often employed, but unfortunately we show that in the case of the DPS protocol, this results in a substantially low key rate. This low key rate is due to a loose estimation of the sum of probabilities regarding three-photon emission whose probability of occurrence is very small. The main contribution of our work is to show that this obstacle can be overcome by exploiting the recently found novel concentration inequality, Kato's inequality. As a result, the key rate of the DPS protocol is drastically improved. For instance, assuming typical experimental parameters, a 3-Mbit secret key can be generated over 77 km for 8.3 hours, which shows the feasibility of DPS QKD under a realistic setup.
Quantum key distribution is used for secure communication between two parties for generation of secret key. Differential Phase Shift Quantum Key Distribution is a new and unique QKD protocol that is different from traditional ones, providing simplicity and practicality. This paper presents Delay Selected DPS-QKD scheme in which it uses a weak coherent pulse train, and features simple configuration and efficient use of the time domain. All detected photon participate to form a secure key bits and resulting in a higher key creation efficiency.