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One important challenge of quantum key distribution is to preserve its unconditional security when a scheme is implemented. In semi-quantum key distribution (SQKD), one of the parties is only able to perform classical operations, thus alleviating the cost of its implementation. Authenticated SQKD (ASQKD) ensures also better security than SQKD against attacks aiming at the identity of the parties. In this regard, Li et al. have proposed a new ASQKD scheme that ensures better efficiency than the first proposed ASQKD scheme of Yu et al. However, both schemes present loopholes in their security. This study presents a new ASQKD without using entanglement, able to achieve higher security than the schemes of Yu et al. and Li et al. Our scheme is also simpler and demands less advanced quantum devices than ASQKD schemes using entanglement.

Historically, the information efficiency of the secret key in quantum key distribution (QKD) schemes based on binary signal formats was limited to 1 bit/particle. An efficient high-dimensional QKD protocol based on qudits transmission with the quantum Fourier transform is proposed. In the proposal, the inherent encoding framework provides a secure solution to key distribution, where the secret information can be hidden into the relative phases of the generated high-dimensional entangled state by performing the quantum Fourier transform and the quantum controlled-NOT gate. After the reverse operations are carried out, the key information can be decoded with the single-particle measurement chosen from two mutually unbiased bases. The secret key taking the form of the high-dimensional quantum state throughout the proposed QKD protocol enables to break the information efficiency limit. Besides, the security of the proposed QKD protocol is guaranteed by the decoy state method and it is proven to be secure even for the photon number splitting attack and the side-channel attack. The cryptographic performance in terms of security and capacity is better than that of traditional cryptographic protocols.

Semiquantum cryptography was proposed to deal with the issue that some players require only partial quantum power, such as preparing or measuring quantum states in the classical basis, which simplifies the implementations of quantum cryptography. However, the efficiency of the existing semiquantum cryptographic protocols was relatively low from a practical point of view. In this paper, we devise improved semiquantum key distribution (SQKD) protocols to improve the efficiency of SQKD protocols. Our improved SQKD protocols utilize the discarded X-SIFT bits in the previous SQKD protocols for improving the efficiency of previous SQKD protocols (Boyer et al. in Phys Rev Lett 99:140501, 2007; Zou et al. in Phys Rev A 79:052312, 2009). Besides, the efficiency of our new protocols can be made asymptotically close to 100% by letting players select their actions asymmetrically. We prove the information theoretical secure of the proposed SQKD protocols against the most general attacks. Our security proof is suitable for the single-state SQKD protocol (Zou et al. in Phys Rev A 79:052312, 2009).

To ensure communication security, it is necessary to verify the identities of the communicators. Two semi-quantum identification protocols with single photons involving two parties, i.e., quantum Alice and classical Bob, are presented. In the first semi-quantum identification protocol, classical Bob can authenticate quantum Alice’s identity without the help of an authenticated classical channel. As for the second one, quantum Alice can verify the identity of classical Bob without the classical measurement ability. Semi-quantum identification is significant to ensure the security of semi-quantum key distribution, semi-quantum secret sharing and so on. The proposed two identification protocols against common attacks can be employed in several existing semi-quantum key distribution protocols based on single photons to resist the man-in-the-middle attack.

Yu et al. have proposed the first authenticated semi-quantum key distribution (ASQKD) without using an authenticated classical channel. This study further proposes two advanced ASQKD protocols. Compared to Yu et al.'s schemes, the proposed protocols ensure better qubit efficiency and require fewer pre-shared keys. Security analyses show that the proposed ASQKD protocols also can be secure against several well-known outside eavesdropper's attacks.

Semiquantum communication permits a communication party with only limited quantum ability (i.e., “classical” ability) to communicate securely with a powerful quantum counterpart and will obtain a significant advantage in practice when the completely quantum world has not been built up. At present, various semiquantum schemes for key distribution, secret sharing and secure communication have been proposed. In a quantum dialogue (QD) scenario, two communicants mutually transmit their respective secret messages and may have equal power (such as two classical parties). Based on delegated quantum computation model, this work extends the original semiquantum model to the authenticated semiquantum dialogue (ASQD) protocols, where two “classical” participants can mutually transmit secret messages without any information leakage and quantum operations are securely delegated to a quantum server. To make the proposed ASQD protocols more practical, we assume that the quantum channel is a collective noise channel and the quantum server is untrusted. The security analysis shows that the proposed protocols are robust even when the delegated quantum server is a powerful adversary.

In a recent paper, the quantum-chaotic key distribution (QCKD) in optical networks was introduced. In the present work, we extend the QCKD theory in two ways: Firstly, we propose to use the dependent Bernoulli trials to model the key generation in QCKD. Using this model, we show that the key generated by QCKD is far from presenting the observed correlations in chaos-based cryptography, and it is very close to the maximum secrecy offered by ideal quantum cryptography. Secondly, we show a new optical scheme for QCKD in which the optical chaotic scheme using optoelectronic oscillators is substituted by nonlinear discrete equations running in computers and the information carrier used is the phase instead of the light polarization. These changes make much easier its implementation with today technology while keeping the same security level guaranteed by chaotic and quantum rules.

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.

We investigate the composable security of unidimensional continuous-variable quantum key distribution (UCVQKD) protocol in generally phase-sensitive channel; the UCVQKD protocol is based on the Gaussian modulation of a single quadrature of the coherent state of light, aiming to provide a simple implementation of key distribution compared to the symmetrically modulated Gaussian coherent-state protocols. This protocol neglects the necessity in one of the quadrature modulations in coherent states and hence reduces the system complexity. To clarify the influence of finite-size effect and the cost of performance degeneration, we establish the relationship of the balanced parameters of the unmodulated quadrature and estimate the precise secure region. Subsequently, we illustrate the composable security of the UCVQKD protocol against collective attacks and achieve the tightest bound of the UCVQKD protocol. Numerical simulations show the asymptotic secret key rate of the UCVQKD protocol, together with the symmetrically modulated Gaussian coherent-state protocols.

The primary goals of security such as authentication, confidentiality, integrity and non-repudiation in communication networks can be achieved with secure key distribution. Quantum mechanisms are highly secure means of distributing secret keys as they are unconditionally secure. Quantum key distribution protocols can effectively prevent various attacks in the quantum channel, while classical cryptography is efficient in authentication and verification of secret keys. By combining both quantum cryptography and classical cryptography, security of communications over networks can be leveraged. Hwang, Lee and Li exploited the merits of both cryptographic paradigms for provably secure communications to prevent replay, man-in-the-middle, and passive attacks. In this paper, we propose a new scheme with the combination of quantum cryptography and classical cryptography for 802.11i wireless LANs. Since quantum cryptography is premature in wireless networks, our work is a significant step forward toward securing communications in wireless networks. Our scheme is known as hybrid quantum key distribution protocol. Our analytical results revealed that the proposed scheme is provably secure for wireless networks.

A proactive quantum secret sharing scheme is proposed, in which the participants can update their key shares periodically. In an updating period, one participant randomly generates the EPR pairs, and the other participants update their key shares and perform the corresponding unitary operations on the particles of the EPR pairs. Then, the participant who generated the EPR pairs performs the Bell-state measurement and updates his key share according to the result of the Bell-state measurement. After an updating period, each participant can change his key share, but the secret is changeless, and the old key shares will be useless even if they have been stolen by the attacker. The proactive property of our scheme is very useful to resist the mobile attacker.

Key management plays a fundamental role in the field of cryptography. In this paper, we propose a novel multiparty quantum key management (QKM) protocol. Departing from single-function quantum cryptography protocols, our protocol has a salient feature in that it accomplishes a complete QKM process. In this process, we can simultaneously realize the functions of key generation, key distribution and key backup by executing the protocol once. Meanwhile, for the first time, we propose the idea of multi-function QKM. Firstly, the secret key is randomly generated by managers via the quantum measurements in $$d$$d-level Bell basis. Then, through entanglement swapping, the secret key is successfully distributed to users. Under circumstances of urgent requirement, all managers can cooperate to recover the users' secret key, but neither of them can recover it unilaterally. Furthermore, this protocol is further generalized into the multi-manager and multi-user QKM scenario. It has clear advantages in the burgeoning area of quantum security group communication. In this system, all group members share the same group key, and group key management is the foundation of secure group communication and hence an important subject of study.

In the existing semiquantum key distribution (SQKD) protocols, the both parties must measure qubits in some bases. In this paper, we show that the classical party's measurement capability is not necessary by constructing an SQKD protocol without invoking the classical Alice's measurement capability. In particular, we prove that the proposed SQKD protocol is completely robust against joint attacks. Compared with the existing SQKD protocols, the number of the quantum states sent by Alice and Bob is decreased.

Nearest private query is a special private query which involves two parties, a user and a data owner, where the user has a private input (e.g., an integer) and the data owner has a private data set, and the user wants to query which element in the owner’s private data set is the nearest to his input without revealing their respective private information. In this paper, we first present a quantum protocol for nearest private query, which is based on quantum oblivious key distribution (QOKD). Compared to the classical related protocols, our protocol has the advantages of the higher security and the better feasibility, so it has a better prospect of applications.

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.

This paper proposes a multi-party semi-quantum secret sharing (MSQSS) protocol which allows a quantum party (manager) to share a secret among several classical parties (agents) based on GHZ-like states. By utilizing the special properties of GHZ-like states, the proposed scheme can easily detect outside eavesdropping attacks and has the highest qubit efficiency among the existing MSQSS protocols. Then, we illustrate an efficient way to convert the proposed MSQSS protocol into a multi-party semi-quantum key distribution (MSQKD) protocol. The proposed approach is even useful to convert all the existing measure–resend type of semi-quantum secret sharing protocols into semi-quantum key distribution protocols.

Guan et al. (Quantum Inf Process 13(11):2355---2374, 2014) proposed a three-party authenticated quantum key distribution protocol which allows two participants to authenticate each other and eventually share a session key between them with the help of a trusted center (TC), who has pre-shared a master key with each participant, respectively. After a successful authentication and key distribution process, TC and the participants update their master keys, respectively. However, this study points out that Guan et al.'s scheme suffers from the intercept-and-measure attack and information leakage problem, and has the synchronization problem.

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.

Recently, Boyer et al. (Phys Rev Lett 99:140501, 2007) introduced a conceptually novel semi-quantum key distribution scheme (BKM07). Tan et al. (Phys Rev Lett 102:098901, 2009) 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, 2009) 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 $${\sim }t$$~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.

In 1984, Bennett and Brassard designed the first quantum key distribution protocol, whose security is based on quantum indeterminacy. Since then, there has been growing research activities, aiming in designing new, more efficient and secure key distribution protocols. The work presents a novel hybrid quantum key distribution protocol. The key distribution is derived from both quantum and classical data. This is why it is called hybrid. The protocol applies extended unitary operations derived from four basic unitary operations and distributed fountain codes. Compared to other protocols published so far, the new one is more secure (provides authentication of parties and detection of eavesdropping) and efficient. Moreover, our protocol still works over noisy and lossy channels.

In this paper, we investigate single-state, semi-quantum key distribution protocols. These are protocols whereby one party is limited to measuring only in the computational basis, while the other, though capable of measuring in both computational and Hadamard bases, is limited to preparing and sending only a single, publicly known qubit state. Such protocols rely necessarily on a two-way quantum communication channel making their security analysis difficult. However, we will show that, for single-state protocols, we need only consider a restricted attack operation by Eve. We will also describe a new single-state protocol that permits "reflections" to carry information and use our results concerning restricted attacks to show its robustness.

We present and demonstrate a novel ultra-long fiber laser key distribution system (UFL-KDS). The scheme quenches the lasing process when in its secure states, thus forming "dark states" which provide simple detection on one hand and increased difficulty of eavesdropping on the other. We analyze the practical aspects of previously studied UFL-KDS schemes as well as those of the one presented here and demonstrate successful key distribution across a 200 km link with bit-rates that can exceed 0.5 kbps. Spectral and temporal passive attack strategies are analyzed and discussed in details.

Recently, Hwang et al. proposed two three-party authenticated quantum key distribution protocols for two communicating parties to establish a session key via a trusted center. They also showed their protocols were secure by using random oracle model. However, their protocols were designed to run in an ideal world. In this paper, we present a more practical protocol by considering some issues, which have not been addressed in their protocols. These issues include (1) session key consistence, (2) online guessing attack, and (3) noise in quantum channels. To deal with these issues, we use error correction code and key evolution. We also give a formal proof for the security of our protocols by using standard reduction, instead of the random oracle model.

This study presents the first authenticated semi-quantum key distribution (ASQKD) protocols without using authenticated classical channels. By pre-sharing a master secret key between two communicants, a sender with advanced quantum devices can transmit a working key to a receiver, who can merely perform classical operations. The idea of ASQKD enables establishment of a key hierarchy in security systems that also eases the key management problem. The proposed protocols are free from several well-known attacks

Information-theoretically secure (ITS) authentication is needed in Quantum Key Distribution (QKD). In this paper, we study security of an ITS authentication scheme proposed by Wegman & Carter, in the case of partially known authentication key. This scheme uses a new authentication key in each authentication attempt, to select a hash function from an Almost Strongly Universal$_2$ hash function family. The partial knowledge of the attacker is measured as the trace distance between the authentication key distribution and the uniform distribution; this is the usual measure in QKD. We provide direct proofs of security of the scheme, when using partially known key, first in the information-theoretic setting and then in terms of witness indistinguishability as used in the Universal Composability (UC) framework. We find that if the authentication procedure has a failure probability $\epsilon$ and the authentication key has an $\epsilon'$ trace distance to the uniform, then under ITS, the adversary's success probability conditioned on an authentic message-tag pair is only bounded by $\epsilon+|\mT|\epsilon'$, where $|\mT|$ is the size of the set of tags. Furthermore, the trace distance between the authentication key distribution and the uniform increases to $|\mT|\epsilon'$ after having seen an authentic message-tag pair. Despite this, we are able to prove directly that the authenticated channel is indistinguishable from an (ideal) authentic channel (the desired functionality), except with probability less than $\epsilon+\epsilon'$. This proves that the scheme is ($\epsilon+\epsilon'$)-UC-secure, without using the composability theorem., Comment: 15 pages

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.