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Quantum key agreement (QKA) is an important cryptographic primitive that plays a pivotal role in private communications. However, in practical implementations of QKA, the flaws in participants' detectors may be exploited to compromise the security and fairness of the protocol. To address this issue, we propose a two-party measurement-device-independent QKA protocol, effectively eliminating all detector-side-channel loopholes. This protocol is based on quantum entanglement swapping and Bell-state measurements, making it feasible under current technological conditions. A thorough security analysis is conducted, demonstrating its ability to guarantee both security and fairness. [ABSTRACT FROM AUTHOR]

It is a fundamental cryptographic capability to establish multipartite anonymous entanglement among multiple parties in future quantum networks, which can be then exploited for further multiparty communication tasks such as conference key agreement, secret sharing or else. Here, we present a practical approach to create multiparty anonymous entanglement without multipartite entanglement. It exploits a measurement-device-independent architecture and naturally removes all detector side channels. We prove its security and compare its performance with the approach based on multipartite Greenberger–Horne–Zeilinger (GHZ) entanglement over certain types of noisy channels. It paves a way for practical multiparty anonymous quantum communication. [ABSTRACT FROM AUTHOR]

Quantum wireless communication networks are an important part of global quantum networks. Here we propose a measurement-device-independent quantum wireless network communication protocol, which can not only close detector-side-channel loopholes launched by malicious nodes but also remedy the drawback of a perfectly shared Greenberger-Horne-Zeilinger state between the nodes. Moreover, the correctness of the generated entanglement between the sender and the receiver is checked. The security analysis shows that the proposed protocol is secure against common attacks from malicious nodes. [ABSTRACT FROM AUTHOR]

Deterministic secure quantum communication (DSQC) is an important primitive of quantum cryptography and has attracted continuous attention. Here, we report the first DSQC protocol based on spatial encoding. The qubit information is encoded in the spatial-mode degree of freedom of photons. A decoy state technique is used to ensure the security of the DSQC protocol. We also analyze the security of the DSQC protocol and show that it is secure against common attacks such as the interception-and-retransmission attack and general entanglement–measurement attack. Without the use of the polarization state of photons, it avoids the degeneration of the states of photons so that it is suitable for long-distance quantum communication. [ABSTRACT FROM AUTHOR]

In quantum key agreement (QKA), a shared key is established among two or more parties where each participant equally contributes its part to the shared key, and none of the participants can determine the shared key alone. Zhou et al. (Electron Lett 40(18):1149, 2004) gave the first QKA protocol based on quantum teleportation and since then quite a few variants and extensions have been proposed. However, none of the existing protocols are device-independent, i.e., all of them assume implicitly that the single-photon states or entangled states supplied to the participants are of certain form. In this work, we exploit the idea of the device-independent dimension witness for independent preparation and measurement devices proposed by Tavakoli (Phys Rev Lett 125:15050, 2020) and connect it with the QKA protocol (Chong and Hwang in Opt Commun 283:1192–1195, 2010) to present the concept of semi-device-independent QKA protocol for the first time. [ABSTRACT FROM AUTHOR]

Recently, a measurement-device-independent protocol for deterministic quantum secret sharing was proposed (Gao et al. in Sci Chin Phys Mech Astron 63(12):120311, 2020). Unfortunately, it was pointed out to be insecure against the participant attack (Yang et al. in Sci Chin Phys Mech Astron 64(6):260321, 2021). However, this participant attack strategy has an assumption that a dishonest agent has to reveal his single-photon state after other agents. Here, we give a more powerful participant attack strategy regardless of the announcement order. [ABSTRACT FROM AUTHOR]

Deterministic secure quantum communication (DSQC) is an important branch of quantum cryptography and has attracted continuous attention. However, in practical DSQC, the receiver's detectors can be subjected to detector-side-channel attacks launched by the outside eavesdropper. Moreover, encoding the information in only one degree of freedom (DOF) of photons makes DSQC inefficient. Here, to remove all the detector side channels and increase single-photons' channel capacity, we report the first high-capacity measurement-device-independent DSQC (HC-MDI-DSQC) protocol by using photons' polarization-spatial-mode DOFs. This method is similar to the idea of MDI quantum key distribution. Theoretical analyses show that it is advantageous in terms of security and efficiency compared with the state-of-the-art DSQC protocols. [ABSTRACT FROM AUTHOR]

A novel quantum multi-hop communication scheme is proposed based on multi-qubit Greenberger–Horne–Zeilinger (GHZ) states and Bell states. We first propose a method where a GHZ state of arbitrary scale is generated efficiently by combining small-scale GHZ states via Bell-state measurements in a distributed manner. Based on this, we present an efficient and economical multi-hop quantum communication protocol. Finally, our scheme is compared with existing quantum multi-hop communication schemes in terms of communication efficiency. [ABSTRACT FROM AUTHOR]

Quantum feedback control (QFBC) and quantum feedforward control (QFFC) are two major techniques for protecting quantum states against decoherence. Based on this, Guo et al. proposed a scheme by combining the QFFC and the minimum-error discrimination (MED) to realize a better effect of discriminating two non-orthogonal states after passing a noisy channel (Phys Rev A 91:022321, 2015) than the scheme without the QFFC. Recently, Cao et al. proposed a novel composite control scheme for protecting such states (Phys Rev A 95:032313, 2017), where QFBC and QFFC are combined. They showed that the performance of the composite control scheme is better than that of the previous control schemes in terms of the success probability and the fidelity. In this paper, we examine the discrimination scheme by combining the composite control and the MED and observe an interesting phenomenon, i.e., better quantum control does not imply better discrimination effect. Finally, we explain this phenomenon. [ABSTRACT FROM AUTHOR]

Guo et al. (Phys Rev A 91(2):022321, 2015) introduced the feed-forward control to realize a better effect of discrimination of two non-orthogonal states against noise. However, the better effect of discrimination is achieved in a probabilistic way. To solve the problem, we introduce the feedback control to discriminate two non-orthogonal states against noise. It is shown that it can improve the effect of discrimination for any pair of non-orthogonal states and any strength of amplitude damping noise largely in a deterministic way. In particular, our optimum probability of discrimination can be higher than that of discriminating two initial non-orthogonal pure states for not only equal a priori probabilities but also unequal a priori probabilities. We also examine the approach in the presence of different noise sources and find it works well for all typical types of noise sources ranging from a single type of noise to the combination of different types of noise. [ABSTRACT FROM AUTHOR]

We present an efficient protocol to rapidly generate a three-dimensional entangled state for two atoms trapped in a cavity with quantum Zeno dynamics and Lewis-Riesenfeld invariants. The required time for the protocol is much shorter than that with adiabatic passage. The influence of various decoherence processes such as atomic spontaneous emission and photon loss on the fidelity of the three-dimensional entangled state is investigated. Numerical simulation demonstrates that the protocol is robust against both the atomic spontaneous emission and cavity decay. Different from Lin et al. (J Opt Soc Am B 33(4):519-524, 2016), the three-dimensional entangled state can be fast generated with only one step. Furthermore, the protocol can be generalized to generate N-dimensional entanglement state. Therefore, we hope the protocol may be useful in quantum information field. [ABSTRACT FROM AUTHOR]

Chen et al. (Phys Rev A 73:012303, 2006) constructed this 'starlike cluster' state, which involves one qubit located at the center and n neighboring two-qubit arms. This genuine entangled state has been used for the construction of 2D and 3D cluster states, topological one-way computation, and dynamical quantum secret sharing. In this paper, we investigate the usefulness of this starlike cluster state and propose a theoretically extensible quantum digital signature scheme. The proposed scheme can be theoretically generalized to more than three participants. Moreover, it retains the merits of no requirements such as authenticated quantum channels and long-term quantum memory. We also give a security proof for the proposed scheme against repudiation and forgery. [ABSTRACT FROM AUTHOR]

Existing classical post-processing (CPP) schemes for quantum key distribution (QKD)-based quantum private queries (QPQs) including the $$kN\rightarrow N$$ , $$N\rightarrow N$$ , and $$rM\rightarrow N$$ ones have been found imperfect in terms of communication efficiency and security. In this paper, we propose a novel CPP scheme for QKD-based QPQs. The proposed CPP scheme reduces the communication complexity and improves the security of QKD-based QPQ protocols largely. Furthermore, the proposed CPP scheme can provide a multi-bit query efficiently. [ABSTRACT FROM AUTHOR]

Cluster states can be exploited for some tasks such as topological one-way computation, quantum error correction, teleportation and dense coding. In this paper, we investigate and propose an arbitrated quantum signature scheme with cluster states. The cluster states are used for quantum key distribution and quantum signature. The proposed scheme can achieve an efficiency of 100 %. Finally, we also discuss its security against various attacks. [ABSTRACT FROM AUTHOR]

All existing quantum oblivious transfer protocols can be achieved when all the members have to be quantum. So what will happen if not all the members are quantum? In this paper, we propose two novel protocols for all-or-nothing oblivious transfer and one-out-of-two oblivious transfer respectively by using single qubit states. Our contribution lies in the fact that the message receiver Bob can use fewer quantum resources so that our protocols relax the requirements of protocol implementation in practice. We analyze the security of the protocols and prove that they are secure against Bob who even has the quantum attack capability. [ABSTRACT FROM AUTHOR]

Recently, Jakobi et al. (Phys Rev A 83, 022301, ) suggested the first practical private database query protocol (J-protocol) based on the Scarani et al. (Phys Rev Lett 92, 057901, ) quantum key distribution protocol. Unfortunately, the J-protocol is just a cheat-sensitive private database query protocol. In this paper, we present an idealized relativistic quantum private database query protocol based on Minkowski causality and the properties of quantum information. Also, we prove that the protocol is secure in terms of the user security and the database security. [ABSTRACT FROM AUTHOR]

A novel private database query protocol with only one quantum state is proposed. The database owner Bob sends only one quantum state to the user Alice. The proposed protocol combines the idea of semiquantum key distribution and private query. It can be implemented in the situation where not all the parties can afford expensive quantum resources and operations. So our proposal is more practical in use. We also prove that the proposed protocol is secure in terms of the user security and the database security. [ABSTRACT FROM AUTHOR]

Recently, Boyer et al. (Phys Rev Lett 99:140501, ) introduced a conceptually novel semi-quantum key distribution scheme (BKM07). Tan et al. (Phys Rev Lett 102:098901, ) showed that classical Bob is unable to detect Eve's eavesdropping by giving a special implementation of BKM07 protocol. In the reply, Boyer et al. (Phys Rev Lett 102:098902, ) gave a solution against the eavesdropping, i.e., Bob may place a filter that allows only photons with approximately specific frequency to pass just at the expected time $${\sim }t$$ . However, their improvement contradicts the descriptions about 'classical.' If the assumption of 'classical' is not considered, we give a delay-photon Trojan-horse attack on BKM07 protocol and its improvement and further present a possible improvement. [ABSTRACT FROM AUTHOR]

We investigate the dynamic watermarking scheme for quantum images using quantum wavelet transform (QWT) proposed by Song et al. (Quantum Inf Process 12(12):3689-3706, ). It is aimed to embed the watermark image into the wavelet coefficients of the quantum carrier image. However, in our opinion, the key procedures of the protocol are wrong. At last, a possible improvement strategy is presented. [ABSTRACT FROM AUTHOR]

Jakobi et al. for the first time proposed a novel and practical quantum private query (QPQ) protocol based on SARG04 (Scarani et al. in Phys Rev Lett 92:057901, ) quantum key distribution protocol (Jakobi et al. in Phys Rev A 83:022301, ). Gao et al. generalized Jakobi et al's protocol and proposed a flexible QPQ protocol (Gao et al. in Opt Exp 20(16):17411-17420, ). When $$\theta <\pi /4$$ , Gao et al's protocol exhibits better database security than Jakobi et al's protocol, but has a higher probability with which Bob can correctly guess the address of Alice's query. In this paper, we propose a flexible B92-based QPQ protocol. Although SARG04 protocol is a modification of B92 protocol and can be seen as a generalization of B92 protocol, our protocol shows different advantages from Gao et al's protocol. It can simultaneously obtain better database security and a lower probability with which Bob can correctly guess the address of Alice's query when $$\theta <\pi /4$$ . By introducing entanglement, the proposed QPQ protocol is robust against channel-loss attack, which also implies lower classical communication complexity. Similar to Gao et al's protocol, it is flexible, practical, and robust against quantum memory attack. [ABSTRACT FROM AUTHOR]

A novel gray-level image encryption/decryption scheme is proposed, which is based on quantum Fourier transform and double random-phase encoding technique. The biggest contribution of our work lies in that it is the first time that the double random-phase encoding technique is generalized to quantum scenarios. As the encryption keys, two phase coding operations are applied in the quantum image spatial domain and the Fourier transform domain respectively. Only applying the correct keys, the original image can be retrieved successfully. Because all operations in quantum computation must be invertible, decryption is the inverse of the encryption process. A detailed theoretical analysis is given to clarify its robustness, computational complexity and advantages over its classical counterparts. It paves the way for introducing more optical information processing techniques into quantum scenarios. [ABSTRACT FROM AUTHOR]

We investigate the quantum watermark strategy for quantum images based on quantum Fourier transform proposed by Zhang et al.(Quantum Inf Process 12(2):793-803, ). It is aimed to embed the watermark image into the Fourier coefficients of the quantum carrier image without affecting the carrier image's visual effect. However, in our opinion the protocol is not clearly described and several steps are ambiguous. Moreover, we argue that the watermarking algorithm claimed by the authors is incorrect. At last, a possible improvement strategy is presented. [ABSTRACT FROM AUTHOR]

In a conventional quantum ( k, n) threshold scheme, a trusted party shares a quantum secret with n agents such that any k or more agents can cooperate to recover the original secret, while fewer than k agents obtain no information about the secret. Is the reconstructed quantum secret same with the original one? Or is the dishonest agent willing to provide a true share during the secret reconstruction? In this paper we reexamine the security of quantum ( k, n) threshold schemes and show how to construct a verifiable quantum ( k, n) threshold scheme by combining a qubit authentication process. The novelty of ours is that it can provide a mechanism for checking whether the reconstructed quantum secret is same with the original one. This mechanism can also attain the goal of checking whether the dishonest agent provides a false quantum share during the secret reconstruction such that the secret quantum state cannot be recovered correctly. [ABSTRACT FROM AUTHOR]

. Chamoli and C.M. Bhandari presented a secure direct communication based on ping-pong protocol[Quantum Inf. Process. 8, 347 (2009)]. M.Naseri analyzed its security and pointed out that in this protocol any dishonest party can obtain all the other one's secret message with zero risk of being detected by using fake entangled particles (FEP attack) [M. Naseri, Quantum Inf. Process. online]. In this letter, we reexamine the protocol's security and discover that except the FEP attack, using a special property of GHZ states, any one dishonest party can also take a special attack, i.e., double-CNOT(Controlled NOT) attack. Finally, a denial-of-service attack is also discussed. [ABSTRACT FROM AUTHOR]

We present a new two-party quantum key agreement (QKA) protocol based on Bell states. The participant transmits Bell states directly by inserting decoy photons in them randomly. The protocol is secure against the outsider attack and participant attack. Finally, it is generalized to multi-party QKA based on Bell states. [ABSTRACT FROM AUTHOR]

In this paper, based on logical GHZ states and logical χ-states, we present four three-party quantum secret sharing protocols immune to the collective-dephasing noise and the collective-rotation noise, respectively. They make full use of the measurement correlation property of multi-particle entangled states and local unitary operations. Compared with existing three-party quantum secret sharing protocols against collective noise, our protocols are the most efficient. Furthermore, these protocols are congenitally free from the Trojan horse attacks. [ABSTRACT FROM AUTHOR]

High-fidelity quantum state transfer is critical for quantum communication and scalable quantum computation. Current quantum state transfer algorithms on the complete bipartite graph, which are based on discrete-time quantum walk search algorithms, suffer from low fidelity in some cases. To solve this problem, in this paper we propose a two-stage quantum state transfer algorithm on the complete bipartite graph. The algorithm is achieved by the generalized Grover walk with one marked vertex. The generalized Grover walk's coin operators and the query oracles are both parametric unitary matrices, which are designed flexibly based on the positions of the sender and receiver and the size of the complete bipartite graph. We prove that the fidelity of the algorithm is greater than 1 - 2 ϵ 1 - ϵ 2 - 2 2 ϵ 1 ϵ 2 or 1 - 2 + 2 2 ϵ 1 - ϵ 2 - 2 + 2 2 ϵ 1 ϵ 2 for any adjustable parameters ϵ 1 and ϵ 2 when the sender and receiver are in the same partition or different partitions of the complete bipartite graph. The algorithm provides a novel approach to achieve high-fidelity quantum state transfer on the complete bipartite graph in any case, which will offer potential applications for quantum information processing. [ABSTRACT FROM AUTHOR]

Quantum walks with memory (QWM) are types of modified quantum walks that record the walker's latest path. The general model of coined QWM is presented in Li et al. (Phys Rev A 93:042323, 2016). In this paper, we present the general Szegedy QWM model and we describe its relationship with the coined QWM model. A coined QWM can be transformed into a Szegedy QWM, while a Szegedy QWM can be transformed into a coined QWM with any partition. These results may help in the analysis of the coined QWM. By transforming a coined QWM into a Szegedy QWM, the essential structure of the coined QWM is revealed. We give an example and we prove that two known QWMs are equal when they have a proper position-dependent coin operator. [ABSTRACT FROM AUTHOR]

Average neighborhood margin maximization (ANMM) is a local supervised metric learning approach, which aims to find projection directions where the local class discriminability is maximized. Furthermore, it has no assumption of class distribution and works well on small sample size. In this work, we address this problem in the quantum setting and present a quantum ANMM algorithm for linear feature extraction. More specifically, a quantum algorithm is designed to construct scatterness and compactness matrices in the quantum state form. Then a quantum algorithm is presented to obtain the features of the testing sample set in the quantum state form. The time complexity analysis of the quantum ANMM algorithm shows that our algorithm may achieve an exponential speedup on the dimension of the sample points D , and a quadratic speedup on the numbers of training samples N and testing samples M compared to the classical counterpart under certain conditions. [ABSTRACT FROM AUTHOR]

The proposed controlled quantum teleportation schemes must prepare the entangled state in advance, hence a novel controlled quantum teleportation scheme based on quantum walks of three coins is proposed, in which the entangled state is generated between the position space and the coin space by conditional shift operator as the quantum channel for controlled quantum teleportation. An unknown single-qubit state in this scheme can be teleported by quantum walks on different quantum structures, such as the line, the cycle, and the complete graph with two vertices. By introducing N -walker quantum walks, an unknown N -qubit state can also be teleported on the complete graph with two vertices. Moreover, based on the controlled quantum teleportation of N -walkers, controlled quantum secure direct communication can be realized without transmitting qubits carrying secret messages over the quantum channel. The scheme can be implemented with 0.8899 fidelity on IBM quantum computer "ibmq_quito." Finally, compared with the proposed schemes, our scheme has the following advantages: (1) The entanglement between the position space and the coin space can be easily generated in quantum walks, and it is not necessary to prepare the entangled state in advance. (2) Only single-particle projection measurements and single-qubit gate operations are required, which have obvious advantages on the measurement basis and operations, and the costs are lower. [ABSTRACT FROM AUTHOR]

A new two-party quantum key agreement (QKA) protocol is proposed based on four-qubit cluster states. Encoded four-qubit cluster states can be transmitted directly by means of order rearrangement operation. In contrast to existing QKA protocols based on four-qubit cluster states, it is unnecessary to perform two-way quantum communication. We analyze the security of this protocol and prove that it is secure in ideal conditions. We also propose the method to ensure the security of this protocol in noisy channel. Finally, we analyze the expansibility of the proposed QKA protocol and propose a three-party QKA protocol based on four-qubit cluster states. [ABSTRACT FROM AUTHOR]

Quantum key agreement (QKA) allows participants to establish a shared key over a quantum channel, and no one of the participants can determine the shared key alone. Actually, particles are usually affected by noise during transmission in the quantum channel, and an aggressor can launch a baleful attack under the cover of noise. In this paper, based on logical Bell states, we propose two robust two-party QKA protocols immune to collective-dephasing noise and collective-rotation noise, respectively. The measurement correlation of quantum entanglement is utilized to establish a shared key. The proposed protocols are globally better in terms of quantum resource cost and qubit efficiency than existing two-party QKA protocols against collective noise. The security analysis demonstrates that they can resist common insider and outsider attacks. [ABSTRACT FROM AUTHOR]

Hash functions play an essential role in many cryptographic applications such as digital signature, integrity authentication, and key derivation. Most of them are iteratively built based on the Merkle-Damgård (MD) structure. Unfortunately the traditional MD structure is suffering from various attacks, and thus the design of new hash functions is emerging. In this paper, inspired by quantum computation, we present a new hash function by introducing alternate single-qubit coin operators into discrete-time quantum walk. The present hash function is classical with classical input and output. The compressive function can be implemented by performing alternate single-qubit coin operators on the coin state controlled by a classical input binary message and then applying the global conditional shift operator on the position state and the coin state. The classical output hash value is generated by making amplification, truncation, and modular operation on the final probability distribution. Numerical simulation and performance comparison show that the present hash function has an excellent property of collision resistance and easier implementation than existing quantum-walk-based hash functions. It promotes more applications of quantum computation in the design of hash functions. [ABSTRACT FROM AUTHOR]

Aiming at the high cost of quantum equipment and the difficulty of preparing discrete variable quantum states, a measurement-device-independent continuous variable semi-quantum key distribution (MDI-CV-SQKD) protocol is proposed. We, respectively, give the prepared-measure model and the entanglement-based (EB) model of the MDI-CV-SQKD protocol. Based on the EB model, we analyze the secret key rate and other performance of the protocol and perform numerical simulations. Then we analyze the amount of information transmitted by the channel under different attacks. As long as the channel parameters meet certain conditions, secure communication can be carried out. Through parameter adjustment, the solution can achieve the maximum secret key rate. The protocol has the advantages of easy preparation of continuous variables quantum states, low cost of semi-quantum user equipment, and high utilization of full quantum users. It also has characteristics such as the unconditional security of the full quantum protocol, the resistance to the detector side-channel attack of the measurement-device-independent protocol, and the extension of the transmission distance. Therefore, this protocol has important practical value. [ABSTRACT FROM AUTHOR]

Many achievements have been made since quantum nonlocality without entanglement was found. A natural question is how many orthogonal product states (OPSs) are needed at least to form a nonlocal set in a given quantum system. In this paper, we achieve some interesting results about nonlocal sets with the less amount of OPSs. Firstly, we construct new nonlocal sets of OPSs with only 6 and 9 members in the C 3 ⊗ C 3 ⊗ C 3 and C 4 ⊗ C 4 ⊗ C 4 quantum systems, respectively. Secondly, we give a general construction of nonlocal set of OPSs with only 3 (d - 1) members in C d ⊗ C d ⊗ C d quantum system for d ≥ 3 . Finally, we compare our work with existing results and make a series of generalizations. The comparison result shows that the nonlocal sets of OPSs constructed by us have the least number of elements in their corresponding quantum systems. [ABSTRACT FROM AUTHOR]

Quantum search is one kind of the most important quantum algorithms, which is the only threat to postquantum cryptography till now. In this paper, we consider the problem of partial searching, where we are interested in part of the information of the item being searched. Then, we present the quantum partial search algorithm with smaller oracles, which reduces the difficulty of designing oracles without errors. The time complexity of this algorithm is smaller than that of the Grover search algorithm in practical instances. Furthermore, we present a punctuated version of the quantum partial search algorithm with smaller oracles to make the algorithm more practical by decreasing the number of iterations further. The punctuated algorithm could be running on several quantum computers in parallel. Taking these factors into consideration, the quantum partial search algorithm with smaller oracles for multiple target items is practical for running on a quantum computer and solving many real problems, such as the Hamiltonian circuit problem and solving systems of nonlinear equations. [ABSTRACT FROM AUTHOR]

The proposed quantum identity authentication schemes only involved authentication between two communicators, but communications with deniability capability are often desired in electronic applications such as online negotiation and electronic voting. In this paper, we proposed a quantum deniable authentication protocol. According to the property of unitary transformation and quantum one-way function, this protocol can provide that only the specified receiver can identify the true source of a given message and the specified receiver cannot prove the source of the message to a third party by a transcript simulation algorithm. Moreover, the quantum key distribution and quantum encryption algorithm guarantee the unconditional security of this scheme. Security analysis results show that this protocol satisfies the basic security requirements of deniable authentication protocol such as completeness and deniability and can withstand the forgery attack, impersonation attack, inter-resend attack. [ABSTRACT FROM AUTHOR]

Recently, Yang et al. (Quantum Inf Process 12:109-117, ) proposed an enhancement on a quantum blind signature based on the two-state vector formalism, afterward a special attack strategy on Yang et al.'s enhanced scheme is put forward, in which the dishonest signer can illegally reveal 25 % of the message of the blind signature requester, but an effective solution has not been presented in their paper. In this paper, we further analyze Yang el al.'s enhanced scheme and find that there is another potential loophole which the blind signature requester can forge the message signer's signature. Then, an improvement scheme is proposed. Finally, analysis results show that our improved scheme can withstand the blind signature requester's forgery attack and the above special attack strategy, and our quantum efficiency will still be the same as the primary scheme. [ABSTRACT FROM AUTHOR]

In this paper, protocols of quantum private comparison of equality (QPCE) are investigated. We study the security of previous QPCE protocols with a semi-honest third party (TP) from the viewpoint of secure multiparty computation and show that QPCE protocol (Chen et al. Quantum Inf Process ) has an obvious security flaw. A vicious inside attacker impersonating TP or the compromised TP colluding with a dishonest inside player can steal other player's secret successfully. An improved efficient and feasible QPCE protocol is proposed. In our improved scheme, only the two players can deduce the results of comparisons based on their shared key, and others will learn no information of the comparison results, even the length of secrets. The cost of communication is also be optimized. Our scheme can resist various kinds of attacks from both the outside eavesdroppers and the inside players, even the TP. [ABSTRACT FROM AUTHOR]

The (k, n)-threshold quantum secret sharing scheme is an important and difficult field in quantum information processing and quantum cryptography. In this paper, the (k, n)-threshold quantum secret sharing scheme based on local operations and classical communication (LOCC-QSS) is investigated. Firstly, in order to effectively study the LOCC-QSS scheme, digital and graphical representations of judgement space are introduced creatively. These representations are simple and convenient. Secondly, an algorithm is designed to search optional states for any given k and n. For optional states, the unambiguous probability equals 0 when x participants cooperate (x < k). Thirdly, a method is proposed to decrease the guessing probability. Some schemes which are more secure than existing ones can be obtained further. Last but not least, the conditions of optimal LOCC-QSS schemes are given for the first time. Our research will be helpful for the development of LOCC-QSS scheme. [ABSTRACT FROM AUTHOR]

Quantum key agreement (QKA) permits participants to constitute a shared key on a quantum channel, and no participants are able to independently determine the shared key. In fact, particles are frequently affected by channel noise in the transmission process of quantum channel. Under the cover of noise, attackers can launch malicious attacks. In this thesis, on account of the usage of entanglement swapping of GHZ state and logical Bell states, we design two two-party QKA protocols which are immune to collective-dephasing noise and collective-rotation noise, respectively. In comparison with the existing QKA protocols of two parties, the proposed protocols have better quantum resource cost and the qubit efficiency in the global scope. Security analysis reveals that they can resist not only attacks by participants but also external attacks. [ABSTRACT FROM AUTHOR]

We present a quantum hash function in a quantum walk framework on Johnson graphs. In this quantum hash function, the message bit decides which coin operator, i.e., Grover operator or DFT operator, is applied on the coin at each step. Then a fixed conditional shift operator is applied to decide the movement of the walker. Compared with existing quantum-walk-based hash functions, the present hash function has a lower collision rate and quantum resource cost. It provides a clue for the construction of other cryptography protocols by introducing the quantum walk model into hash functions. [ABSTRACT FROM AUTHOR]

We investigate the distillability of bipartite quantum states in terms of positive and completely positive maps. We construct the so-called generalized Choi states and show that it is distillable when it has negative partial transpose. We convert the distillability problem of 2-copy n × n Werner states into the determination of the positivity of an Hermitian matrix. We obtain several sufficient conditions by which the positivity holds. Further, we investigate the case n = 3 by the classification of 2 × 3 × 3 pure states. [ABSTRACT FROM AUTHOR]

In this paper, we presented a controlled bidirectional remote state preparation scheme which used the six-qubit entangled state as quantum channel. In our scheme, Alice and Bob can prepare simultaneously an arbitrary single-qubit state in each other's place with the control of the supervisor Charlie. The success probability for our scheme reaches unit. Furthermore, we analyze the expression of quantum channel for controlled bidirectional remote state preparation. Finally, we discuss the security of our scheme, the detailed security analysis shows that the supervisor Charlie's control can greatly improve the security of our scheme. [ABSTRACT FROM AUTHOR]

Recently, some quantum blind signature protocols have been proposed. However, the previous schemes cannot satisfy the unlinkability requirement. To overcome the drawback of unlinkability in the previous schemes, we propose a new quantum blind signature based on Bell states with the help of an authentic party. In this paper, we provide a method to inject a randomizing factor into a message when it is signed by the signer and then get rid of the blind factor from the blinded signature when it is verified by the verifier. Even when the message owner publishes the message-signature pair, the signer cannot identify the association between the message-signature pair and the blind signature he generated. Therefore, our scheme really realizes unlinkability property. At last, analysis results show that this scheme satisfies the basis security requirements of a weak signature such as no-counterfeiting, no-disavowing, blindness and traceability, and our total efficiency is not less than the previous schemes. [ABSTRACT FROM AUTHOR]

A novel quantum deniable authentication protocol based on single photons is proposed. In this scheme, the message sender and the specified receiver will first agree a new shared secret key by key update phases with the help of a third center, where only they can encrypt and decrypt the message by using the new shared secret key. Hence, this scheme can guarantee that only the specified receiver can identify the true source of a given message and the specified receiver cannot prove the source of the message to a third party by a transcript simulation algorithm. Compared with our previous scheme (Shi et al. in Quantum Inf Process 13:1501-1510, ), this scheme has the remarkable advantages of the higher qubit efficiency and consuming fewer quantum resources. Finally, security analysis results show that this scheme satisfies known key security and the basic security requirements of deniable authentication protocol such as completeness and deniability, and can withstand forgery attack, impersonation attack and inter-resend attack. [ABSTRACT FROM AUTHOR]

Quantum walks have received much attention due to their many potential applications for quantum information processing in recent years. In this paper, we propose a novel class of universal and flexible quantum information splitting scheme of an arbitrary qubit and d-dimensional qudit via using the model of quantum walks with multiple coins for the first time. Firstly, for splitting an arbitrary qubit into N parts, quantum walks on the line with N + 1 coins, which are homogeneous and position dependent, are used, respectively. In addition, it can be generalized to the model of quantum walks on the cycle for fulfilling this scheme. Secondly, for distributing an unknown d-dimensional qudit into N parts, quantum walks with N + 1 coins are used on the complete graph and the d-regular graph, respectively. Our scheme has two significant merits: (i) It is universal and flexible, which implies that based on the different quantum walks structures, not only an unknown qubit but also d-dimensional qudit can be shared; (ii) the prior entangled state is not necessarily prepared and the entanglement measurement is not needed, which make this scheme more convenient for the agents in applications on a network. This work opens wider application purpose of quantum walks and provides inspiration to explore the potential applications of quantum walks. [ABSTRACT FROM AUTHOR]