Orthogonal-state-based deterministic secure quantum communication without actual transmission of the message qubits

Recently, an orthogonal-state-based protocol of direct quantum communication without actual transmission of particles is proposed by Salih et al. (Phys Rev Lett 110:170502, 2013) using chained quantum Zeno effect. The counterfactual condition (claim) of Salih et al. is weakened here to the extent that transmission of particles is allowed, but transmission of the message qubits (the qubits on which the secret information is encoded) is not allowed. Remaining within this weaker (non-counterfactual) condition, an orthogonal-state-based protocol of deterministic secure quantum communication is proposed using entanglement swapping, where actual transmission of the message qubits is not required. Further, it is shown that there exists a large class of quantum states that can be used to implement the proposed protocol. The security of the proposed protocol originates from monogamy of entanglement. As the protocol can be implemented without using conjugate coding, its security is independent of non-commutativity.     

Comment on “Dynamic quantum secret sharing”

Hsu et al. (Quantum Inf Process 12:331–344,2013) proposed a dynamic quantum secret sharing (DQSS) protocol using the entanglement swapping of Bell states for an agent to easily join (or leave) the system. In 2013, Wang and Li (Quantum Inf Process 12(5):1991–1997, 2013) proposed a collusion attack on Hsu et al.’s DQSS protocol. Nevertheless, this study points out a new security issue on Hsu et al.’s DQSS protocol regarding to the honesty of a revoked agent. Without considering this issue, the DQSS protocol could be failed to provide secret sharing function.     

Semi-quantum protocol for deterministic secure quantum communication using Bell states

Based on Bell states, this paper proposes a semi-quantum protocol enabling the limited semi-quantum or “classical” user Bob to transmit the secret message to a fully quantum Alice directly. A classical user is restricted to measure, prepare, reorder and send quantum states only in the classical basis \( \{ \left| 0 \right\rangle ,\left| 1 \right\rangle \} \). The protocol must rely on the quantum Alice to produce Bell states, perform Bell basis measurement and store qubits, but the classical party Bob does not require quantum memory. Security and efficiency of the proposed schemes have been discussed. The analysis results show that the protocol is secure against some eavesdropping attacks and the qubit efficiency of the protocol is higher than the other related semi-quantum protocols.     

Secure multiparty quantum secret sharing with the collective eavesdropping-check character

Combining the block transmission in Long and Liu (Phys Rev A 65:032302, 2002) and the double operations in Lin et al. (Opt Commun 282:4455, 2009), we propose a secure multiparty quantum secret sharing protocol with the collective eavesdropping-check character. In this protocol, only the boss needs to prepare Bell states and perform Bell state measurements, and all agents only perform local operations, which makes this protocol more feasible with the current technique. Incidentally, we show that the other half of secret messages in Lin et al. protocol (Opt Commun 282:4455, 2009) may also be eavesdropped.     

Double C-NOT attack and counterattack on ‘Three-step semi-quantum secure direct communication protocol’

Recently, Zou and Qiu (Sci China Phys Mech Astron 57:1696–1702, 2014) proposed a three-step semi-quantum secure direct communication protocol allowing a classical participant who does not have a quantum register to securely send his/her secret message to a quantum participant. However, this study points out that an eavesdropper can use the double C-NOT attack to obtain the secret message. To solve this problem, a modification is proposed.     

Cryptanalysis and improvement of efficient quantum dialogue using entangled states and entanglement swapping without information leakage

The novel quantum dialogue (QD) protocol by using the three-dimensional Bell states and entanglement swapping (Wang et al. in Quantum Inf Process 15(6):2593–2603, 2016) is analyzed. It is shown that there is the information leakage problem in this QD protocol. To be specific, one quarter information of the secret messages exchanged is leaked out unconsciously. Afterward, it is improved to a truly secure one without information leakage. Besides, the security of the improved QD protocol is analyzed in detail. It is shown that the improved QD protocol has some obvious features compared with the original one.     

Measurement device-independent quantum dialogue

Very recently, the experimental demonstration of quantum secure direct communication (QSDC) with state-of-the-art atomic quantum memory has been reported (Zhang et al. in Phys Rev Lett 118:220501, 2017). Quantum dialogue (QD) falls under QSDC where the secrete messages are communicated simultaneously between two legitimate parties. The successful experimental demonstration of QSDC opens up the possibilities for practical implementation of QD protocols. Thus, it is necessary to analyze the practical security issues of QD protocols for future implementation. Since the very first proposal for QD by Nguyen (Phys Lett A 328:6–10, 2004), a large number of variants and extensions have been presented till date. However, all of those leak half of the secret bits to the adversary through classical communications of the measurement results. In this direction, motivated by the idea of Lo et al. (Phys Rev Lett 108:130503, 2012), we propose a measurement device-independent quantum dialogue scheme which is resistant to such information leakage as well as side-channel attacks. In the proposed protocol, Alice and Bob, two legitimate parties, are allowed to prepare the states only. The states are measured by an untrusted third party who may himself behave as an adversary. We show that our protocol is secure under this adversarial model. The current protocol does not require any quantum memory, and thus, it is inherently robust against memory attacks. Such robustness might not be guaranteed in the QSDC protocol with quantum memory (Zhang et al. 2017).     

Cryptanalysis on authenticated semi-quantum key distribution protocol using Bell states

Recently, Yu et al. (Quantum Inf Process 13(6):1457–1465, 2014) proposed the first semi-quantum scheme without the need of a classical channel to generate a secret key, while employing a “master key” and the entanglement properties of Bell states. This study points out a vulnerability that allows a malicious person to recover a partial master key and to launch a successful Man-In-The-Middle attack. Accordingly, we present the most likely leakage information scenarios where an outside attacker affects the security of the proposed protocol.     

Bidirectional controlled quantum teleportation and secure direct communication using five-qubit entangled state

A scheme is presented to implement bidirectional controlled quantum teleportation (QT) by using a five-qubit entangled state as a quantum channel, where Alice may transmit an arbitrary single qubit state called qubit A to Bob and at the same time, Bob may also transmit an arbitrary single qubit state called qubit B to Alice via the control of the supervisor Charlie. Based on our channel, we explicitly show how the bidirectional controlled QT protocol works. By using this bidirectional controlled teleportation, espcially, a bidirectional controlled quantum secure direct communication (QSDC) protocol, i.e., the so-called controlled quantum dialogue, is further investigated. Under the situation of insuring the security of the quantum channel, Alice (Bob) encodes a secret message directly on a sequence of qubit states and transmits them to Bob (Alice) supervised by Charlie. Especially, the qubits carrying the secret message do not need to be transmitted in quantum channel. At last, we show this QSDC scheme may be determinate and secure.     

Enhancement on ��quantum blind signature based on two-state vector formalism��

Recently, Su et?al. (Opt Comm 283:4408?C4410, 2010) proposed a quantum blind signature based on the two-state vector formalism. Their protocol is rather practical because the signer and the blind signature requester only have to perform measurement operations to complete the quantum blind signature. This study points out that a dishonest signer in their scheme can reveal the blind signature requester??s secret key and message without being detected by using Trojan horse attacks or the fake photon attack. A modified scheme is then proposed to avoid these attacks.     

Improvements on “multiparty quantum key agreement with single particles”

Recently, Liu et al. (Quantum Inf Process 12: 1797–1805, 2013) proposed a secure multiparty quantum key agreement (MQKA) protocol with single particles. Their protocol allows N parties to negotiate a secret session key in such away that (1) outside eavesdroppers cannot gain the session key without introducing any errors; (2) the session key cannot be determined by any non-trivial subset of the participants. However, the particle efficiency of their protocol is only $\frac{1}{(k+1)N(N-1)}$ . In this paper, we show that the efficiency of the MQKA protocol can be improved to $\frac{1}{N(k+1)}$ by introducing two additional unitary operations. Since, in some scenarios, the secret keys are confidential, neither party is willing to divulge any of the contents to the other. Therefore, in our protocol, no participant can learn anything more than its prescribed output, i.e., the secret keys of the participants can be kept secret during the protocol instead of being exposed to others, thus, the privacy of the protocol is also improved. Furthermore, we explicitly show the scheme is secure.     

Protocols of quantum key agreement solely using Bell states and Bell measurement

Two protocols of quantum key agreement (QKA) that solely use Bell state and Bell measurement are proposed. The first protocol of QKA proposed here is designed for two-party QKA, whereas the second protocol is designed for multi-party QKA. The proposed protocols are also generalized to implement QKA using a set of multi-partite entangled states (e.g., 4-qubit cluster state and \(\Omega \) state). Security of these protocols arises from the monogamy of entanglement. This is in contrast to the existing protocols of QKA where security arises from the use of non-orthogonal state (non-commutativity principle). Further, it is shown that all the quantum systems that are useful for implementation of quantum dialogue and most of the protocols of secure direct quantum communication can be modified to implement protocols of QKA.     

Efficient bidirectional quantum secure communication with two-photon entanglement

An efficient bidirectional quantum secure communication protocol is proposed with two-photon entanglement. Compared with the previous protocol proposed by Shi et al., our protocol can achieve higher efficiency. Meanwhile, for the same length secret messages, only half of entangled photon pairs need to be prepared in our protocol. And the number of classical bits in public classical communication is also a half of that in the previous protocol. Moreover, the information leakage does not exist in our scheme.     

Cryptanalysis of a multiparty quantum key agreement protocol based on commutative encryption

Recently, Sun et al. (Quantum Inf Process 15(5):2101–2111, 2016) proposed an efficient multiparty quantum key agreement protocol based on commutative encryption. The aim of this protocol is to negotiate a secret shared key among multiple parties with high qubit efficiency as well as security against inside and outside attackers. The shared key is the exclusive-OR of all participants’ secret keys. This is achieved by applying the rotation operation on encrypted photons. For retrieving the final secret key, only measurement on single states is needed. Sun et al. claimed that assuming no mutual trust between participants, the scheme is secure against participant’s attack. In this paper, we show that this is not true. In particular, we demonstrate how a malicious participant in Sun et al.’s protocol can introduce “a” final fake key to target parties of his choice. We further propose an improvement to guard against this attack.     

基于贝尔态的半量子安全直接通信协议

针对量子通信网络构建成本昂贵且效率低下的问题,基于贝尔态粒子和半量子理论,提出了一种易于实现的量子安全直接通信模型。首先,量子态的制备、Bell基测量等复杂操作交由拥有全部量子能力的服务端完成,用户端只需完成投影测量或者直接反射两种简单操作;其次,通信双方传输秘密信息前建立的量子信道以及提前共享的安全密钥,可以严格保障秘密信息不被泄露;最后,通过设计的编码规则,使得协议只使用较少量子资源就完成高效的秘密信息直接传输。通过计算可得,提出的量子安全直接通信模型粒子传输效率达到7.69%,安全模型分析表明了提出的通信模型在各种常见的攻击策略下都是安全可靠的。     

Cryptanalysis of a sessional blind signature based on quantum cryptography

A digital signature is a mathematical scheme for demonstrating the authenticity of a digital message or document. A blind signature is a form of digital signature in which the content of a message is disguised (blinded) before it is signed to protect the privacy of the message from the signatory. For signing quantum messages, some quantum blind signature protocols have been proposed. Recently, Khodambashi et al. (Quantum Inf Process 13:121, 2014) proposed a sessional blind signature based on quantum cryptography. It was claimed that these protocol could guarantee unconditional security. However, after our analysis, we find that the signature protocol will cause the key information leakage in the view of information theory. Taking advantage of loophole, the message sender can succeed in forging the signature without the knowledge of the whole exact key between the verifier and him. To conquer this shortcoming, we construct an improved protocol based on it and the new protocol can resist the key information leakage attacks.     

The local distinguishability of any three generalized Bell states

We study the problem of distinguishing maximally entangled quantum states by using local operations and classical communication (LOCC). A question of fundamental interest is whether any three maximally entangled states in \({\mathbb {C}}^d\otimes {\mathbb {C}}^d (d\ge 4)\) are distinguishable by LOCC. In this paper, we restrict ourselves to consider the generalized Bell states. And we prove that any three generalized Bell states in \({\mathbb {C}}^d\otimes {\mathbb {C}}^d (d\ge 4)\) are locally distinguishable.     

Security of a single-state semi-quantum key distribution protocol

Semi-quantum key distribution protocols are allowed to set up a secure secret key between two users. Compared with their full quantum counterparts, one of the two users is restricted to perform some “classical” or “semi-quantum” operations, which potentially makes them easily realizable by using less quantum resource. However, the semi-quantum key distribution protocols mainly rely on a two-way quantum channel. The eavesdropper has two opportunities to intercept the quantum states transmitted in the quantum communication stage. It may allow the eavesdropper to get more information and make the security analysis more complicated. In the past ten years, many semi-quantum key distribution protocols have been proposed and proved to be robust. However, there are few works concerning their unconditional security. It is doubted that how secure the semi-quantum ones are and how much noise they can tolerate to establish a secure secret key. In this paper, we prove the unconditional security of a single-state semi-quantum key distribution protocol proposed by Zou et al. (Phys Rev A 79:052312, 2009). We present a complete proof from information theory aspect by deriving a lower bound of the protocol’s key rate in the asymptotic scenario. Using this bound, we figure out an error threshold value such that for all error rates that are less than this threshold value, the secure secret key can be established between the legitimate users definitely. Otherwise, the users should abort the protocol. We make an illustration of the protocol under the circumstance that the reverse quantum channel is a depolarizing one with parameter q. Additionally, we compare the error threshold value with some full quantum protocols and several existing semi-quantum ones whose unconditional security proofs have been provided recently.     

Cryptanalysis of enhancement on “quantum blind signature based on two-state vector formalism”

Recently, Yang et al. (Quantum Inf Process 12(1):109, 2013) proposed an enhanced quantum blind signature based on two-taste vector formalism. The protocol can prevent signatory Bob from deriving Alice’s message with invisible photon eavesdropping attack or fake photon attack. In this paper, we show that the enhanced protocol also has a loophole that Alice can utilize an entanglement swapping attack to obtain Bob’s secret key and forge Bob’s valid signature at will later. Then, we reanalyze two existing protocols and try to find some further methods to fix them.     

Quantum dialogue protocols immune to collective noise

This work proposes two quantum dialogue protocols, each of which is robust against one of the following two kinds of collective noise: collective-dephasing noise and collective-rotation noise. Both quantum dialogue protocols are constructed from four-qubit DF states that consist of two Bell states. The receiver simply performs two Bell state measurements to obtain the secret message. Moreover, the proposed protocols are free from information leakage because some shared private quantum states are established in the new protocols to allow the legitimate users to exchange their secret messages securely.