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.
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.
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 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.
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.
The quantum digital signature (QDS) has attracted much attention as it ensures the nonrepudiation, unforgeability, and transferability of signature messages based on information-theoretic security. Amiri et al. ( Phys. Rev. A 93 032325 ) proposed the first practical QDS protocol based on orthogonal coding, which has realized information-theoretic security and become the mainstream paradigm in QDS research. The procedure of QDS involves two essential stages, the one is the distribution stage, in which Alice-Bob and Alice-Charlie individually utilize the three-intensity decoy-state quantum key distribution protocol but without error correction or privacy amplification, namely, key-generation protocol, to generate correlated bit strings, the other is the messaging stage, in which Alice transmits signature messages to the two recipients. However, previous theoretical and experimental studies both overlooked the modulation errors that may be introduced in the state preparation process due to the imperfections in modulator devices. Under the traditional framework of GLLP analysis method, these errors will significantly reduce the actual signature rates. Therefore, we propose a state-preparation-error tolerant QDS and use parameter analysis to characterize the state preparation error to make the simulation analysis more realistic. In addition, we analyze the signature rates of the present scheme by using the three-intensity decoy-state method. Compared with previous QDS protocols, our protocol almost shows no performance degradation under practical state preparation errors and exhibits a maximum transmission distance around 180 km. Furthermore, state preparation errors do not have a significant influence on the bit error rate induced by normal communication between the legitimate users or the one produced by an eavesdropper. These results prove that the method proposed in this paper has excellent robustness against state preparation errors and it can achieve much higher signature rates and signature distances than other standard methods. Besides, signature rates are basically unchanged under different total pulse numbers, which shows that our protocol also has good robustness against the finite-size effect. Additionally, in the key generation process, our method is only required to prepare three quantum states, which will reduce the difficulty of experiment realizations. Furthermore, the proposed method can also be combined with the measurement-device-independent QDS protocol and the twin-field QDS protocol to further increase the security level of QDS protocol. Therefore, our work will provide an important reference value for realizing the practical application of QDS in the future.
Quantum digital signatures (QDSs) allow the sending of messages from one sender to multiple recipients, with the guarantee that messages cannot be forged or tampered with. Additionally, messages cannot be repudiated--if one recipient accepts a message, she is guaranteed that others will accept the same message as well. While messaging with these types of security guarantees are routinely performed in the modern digital world, current technologies only offer security under computational assumptions. QDSs, on the other hand, offer security guaranteed by quantum mechanics. All thus far proposed variants of QDSs require long-term, high quality quantum memory, making them unfeasible in the foreseeable future. Here, we present a QDS scheme where no quantum memory is required, which also needs just linear optics. This makes QDSs feasible with current technology.
Agile cryptography allows for a resource-efficient swap of a cryptographic core in case the security of an underlying classical cryptographic algorithm becomes compromised.Conversely, versatile cryptography allows the user to switch the cryptographic task without requiring any knowledge of its inner workings.In this paper, we suggest how these related principles can be applied to the field of quantum cryptography by explicitly demonstrating two quantum cryptographic protocols, quantum digital signatures (QDS) and quantum secret sharing (QSS), on the same hardware sender and receiver platform.Crucially, the protocols differ only in their classical postprocessing.The system is also suitable for quantum key distribution (QKD) and is highly compatible with deployed telecommunication infrastructures, since it uses standard quadrature phase-shift keying encoding and heterodyne detection.For the first time, QDS protocols are modified to allow for postselection at the receiver, enhancing protocol performance.The cryptographic primitives QDS and QSS are inherently multipartite, and we prove that they are secure not only when a player internal to the task is dishonest, but also when (external) eavesdropping on the quantum channel is allowed.In our first proof-of-principle demonstration of an agile and versatile quantum communication system, the quantum states are distributed at GHz rates.A 1-bit message may be securely signed using our QDS protocols in less than 0.05 ms over a 2-km fiber link and in less than 0.2 s over a 20-km fiber link.To our knowledge, this also marks the first demonstration of a continuous-variable direct QSS protocol.