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Journal of Physics Communications

Differential-phase-shift quantum digital signature without disclosing measurement information

Kyo Inoue, Toshimori Honjo

Published Jun 8, 2022• 4 citations
Publisher

Abstract

Abstract A novel quantum digital signature (QDS) scheme using differential-phase-shift signal is presented. A sender broadcasts a weak coherent pulse train with 0 or π phase to receivers, who measure its relative phases using delay interferometers with photon detectors and then employ the measurement results as authentication keys. The key distribution stage is completed with this signal transmission. Neither exchange of basis information between the sender and receivers nor exchange of a portion of a sifted key between the receivers with each other are conducted, unlike conventional QDS protocols. Therefore, our system is simpler than conventional ones. The security of the proposed scheme is discussed, and calculations evaluating system parameters to guarantee the QDS operation, such as the key length and authentication threshold, are presented.

DOI
10.1088/2399-6528/ac7705

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Abstract A novel quantum digital signature (QDS) scheme using differential-phase-shift signal is presented. A sender broadcasts a weak coherent pulse train with 0 or π phase to receivers, who measure its relative phases using delay interferometers with photon detectors and then employ the measurement results as authentication keys. The key distribution stage is completed with this signal transmission. Neither exchange of basis information between the sender and receivers nor exchange of a portion of a sifted key between the receivers with each other are conducted, unlike conventional QDS protocols. Therefore, our system is simpler than conventional ones. The security of the proposed scheme is discussed, and calculations evaluating system parameters to guarantee the QDS operation, such as the key length and authentication threshold, are presented.
A novel quantum digital signature (QDS) scheme, called "differential quadrature phase-shift QDS," is presented. A message sender broadcasts a weak coherent pulse train with four phases of {0, π/2, π, 3π/2} and recipients create their own authentication keys from the broadcasted signal. Unlike conventional QDS protocols, there is no post-processing of information exchange between the sender and recipients and that between the recipients. Therefore, secured channels and/or authenticated channels for information exchange are not needed, and the key creation procedure is simpler than that of conventional QDS. Security issues are also discussed, using binominal distributions instead of Hoeffding's inequality utilized in conventional QDS studies, and calculation examples for system conditions achieving the QDS function are presented.
Abstract A quantum conference key agreement (QCKA) protocol based on differential-phase-shift quantum key distribution is presented, which provides a common secret key for secure communication between more than two parties. In the proposed protocol, one party simultaneously broadcasts a weak coherent pulse train with {0, π} phases to multiple parties that measure the phase differences between adjacent pulses using a delay interferometer followed by photon detectors, and the transmitter and receivers share secret key bits from the coincident counts in the receivers. The system setup and operation are simpler than those of conventional QCKA schemes that use a multipartite quantum entanglement state. The key creation performance is evaluated by considering the eavesdropping probability. The results indicate that the proposed scheme offers better performance than the conventional entanglement-based QCKA system.
The quantum digital signature (QDS) is a quantum communication technology that distributes authentication keys to candidates of message recipients who will confirm if a message received afterward is the legitimate one, referring to the authentication keys. Although accommodating many recipients may be one of the significant QDS system performances, conventional QDS protocols seem indifferent to this issue. In this study, we investigate the number of accommodable recipients in recently proposed differential-phase-shift (DPS) QDS and differential-quadrature-phase-shift (DQPS) QDS systems. They are unique QDS protocols in which quantum signals are broadcasted to all recipients simultaneously, and there is no post data-processing between the sender and recipients, which is favorable to accommodate a large number of recipients. We analyze the system conditions required to satisfy the QDS criteria, and evaluate the maximum number of recipients. The results indicate that around 100 recipients can be accommodated in a 100-km transmission system.
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.
One of the simplest methods for implementing quantum key distribution over fiber-optic communication is the Bennett-Brassard 1984 protocol with phase encoding (PE-BB84 protocol), in which the sender uses phase modulation over double pulses from a laser and the receiver uses a passive delayed interferometer. Using essentially the same setup and by regarding a train of many pulses as a single block, one can carry out the so-called differential-quadrature-phase-shift (DQPS) protocol, which is a variant of differential-phase-shift (DPS) protocols. Here we prove the security of the DQPS protocol based on an adaptation of proof techniques for the BB84 protocol, which inherits the advantages arising from the simplicity of the protocol, such as accommodating the use of threshold detectors and simple off-line calibration methods for the light source. We show that the secure key rate of the DQPS protocol in the proof is eight-thirds as high as the rate of the PE-BB84 protocol.
Digital signatures ensure the integrity of a classical message and the authenticity of its sender. Despite their far-reaching use in modern communication, currently used signature schemes rely on computational assumptions and will be rendered insecure by a quantum computer. We present a quantum digital signatures (QDS) scheme whose security is instead based on the impossibility of perfectly and deterministically distinguishing between quantum states. Our continuous-variable (CV) scheme relies on phase measurement of a distributed alphabet of coherent states and allows for secure message authentication against a quantum adversary performing collective beamsplitter and entangling-cloner attacks. Crucially, in the CV setting we allow for an eavesdropper on the quantum channels and yet retain shorter signature lengths than previous protocols with no eavesdropper. This opens up the possibility to implement CV QDS alongside existing CV quantum key distribution platforms with minimal modification.