In the Internet of Medical Things (IoMT), sensors automatically collect data and transmit it to hospital servers, where doctors provide professional medical advice. The emergence of IoMT has significantly reduced the burden on chronic-disease patients and improved their life security. However, the transmission of patients' medical data still faces serious confidentiality and integrity risks. This paper proposes a novel healthcare-system architecture that integrates a controlled-authentication semi-quantum key-negotiation (SQKN) protocol, leveraging the unconditional security of quantum cryptography to mitigate potential data attacks. The hospital server acts as a trusted controller that supervises every protocol run and authenticates all participants, which effectively thwarts man-in-the-middle and identity-spoofing attacks. The semi-quantum design further minimizes the quantum-device burden on patients' side. Experimental simulation under realistic noise (QBER approximate to 0.03 at 0.02/0.04 noise level, 3 000 shots) shows the protocol keeps the quantum-bit error rate below 3 %, while the overall key-generation efficiency reaches 92 %, demonstrating that the scheme resists known attacks and maintains high quantum efficiency for safeguarding IoMT data security.

In the field of smart healthcare, video consultation has become a key way to provide medical services for remote patients. In this process, it is essential to ensure the legal identity of both parties to the communication and to protect patient privacy data from unlawful interception and tampering. Therefore, a controlled quantum authentication confidential communication protocol is proposed by using the entanglement exchange ability and measurement correlation of Bell states. With the assistance of a trusted third party, the protocol first achieves the mutual authentication of the communication parties, so as to prevent malicious users from communicating by pretending to be medical specialists or patients. The trusted party then further assists the communicating parties in generating two implicit shared keys, which they use to encrypt the message and its digest, ensuring that the patient's sensitive data is not intercepted or tampered with. In addition, the quantum sequences are transmitted only once in the channel, reducing the loss and noise effects caused by multiple transmissions. Security analysis shows that the protocol can effectively resist participant attacks and outside attacks. In addition, performance analysis provides computation in terms of qubit efficiency and experimental simulation results of the protocol.

In Wise Information Technology of Medicine, to ensure both confidentiality and integrity of the data created during online joint consultations, and to solve the problem that ordinary users cannot afford expensive quantum devices and are vulnerable to man-in-the-middle attacks during communication, this article proposes a three-party controlled authentication semiquantum key agreement protocol, leveraging the measurement retransmission operation and the entanglement properties of cluster states. With the help of a trusted controller with full quantum capabilities, the identities of three semiquantum parties are authenticated, and a shared key is negotiated fairly for subsequent communication. Since the semiquantum participants only need to perform simple quantum state preparation, measurement, and reflection operations, the protocol reduces the requirements for participants’ capabilities and equipment. Moreover, the protocol prevents man-in-the-middle attacks by authenticating the identity of participants. The security evaluation demonstrates that the protocol is capable of effectively defending against both internal participant threats and external intrusions. Moreover, a comparison with existing semiquantum key agreement protocols reveals that this protocol offers certain advantages when its functionality and performance are comprehensively evaluated.

The rapid growth of the Internet of Vehicles (IoV) raises critical cybersecurity and privacy concerns. Traditional centralized authentication faces challenges like high latency and single-point failures. Blockchain enables decentralized, tamper-proof identity verification, while fog computing distributes authentication tasks across local nodes, reducing delays.This paper proposes a lightweight anonymous authentication protocol and trust management model for IoV, combining blockchain and fog computing. The protocol improves efficiency and security by optimizing fog node selection and authentication processes. Additionally, the trust model ensures traceability and transparency in vehicle interactions. Security and performance analyses confirm the scheme's robustness and efficiency.

Objective Quantum cryptography uses quantum states as the carriers of information transmission and transmits information between authorized users through quantum channels. Different from that of traditional cryptography, the security of quantum cryptography is guaranteed by the basic principles of quantum mechanics. Therefore, it is theoretically unconditionally secure. In recent years, quantum cryptography has received extensive attention from many researchers engaged in cryptography, and has gradually developed into a popular research direction in the field of cryptography. Specifically, the quantum key agreement is an important research topic in quantum cryptography. It enables all participants to jointly negotiate a session key through a secure quantum channel, and each participant's contribution to the negotiated key is the same. On the one hand, due to the high cost and scarce resources, it is difficult for the vast majority of participants to have well-performing quantum devices. Therefore, in order to facilitate the implementation of the protocol, it is necessary to simplify the quantum operations of the participants. In response to this problem, some scholars have proposed a semi-quantum key agreement protocol. The semi-quantum key agreement protocol requires that one of the participants in the protocol has complete quantum capabilities, and the remaining participants only have semi-quantum capabilities. Moreover, the semi-quantum participants can only perform the following two operations: i) reflection operation. No operation is performed on the received particles, and the received particles are returned directly. ii) Measurement operation. Z-based measurement is performed on the received particles, and new particles are prepared according to the measurement results. On the other hand, since participants may be attacked by man-in-the-middle in the process of key agreement, it is necessary to authenticate participants before the key agreement. In recent years, researchers have also proposed some quantum key agreement protocols with mutual authentication. In practical application scenarios, in order to facilitate the implementation of the protocol, it is necessary to design a semi-quantum key agreement protocol with lower requirements for participants ability and equipment. In order to prevent external attackers from counterfeiting authorized users to steal shared keys, the protocol needs to have a mutual authentication function. Therefore, it is necessary to design a semi-quantum key agreement protocol with mutual authentication. Methods Based on the Bell state, we propose a two-party semi-quantum key agreement protocol with a mutual authentication function, where Alice is a full quantum participant and Bob is a semi-quantum participant. The two sides achieve mutual authentication of identity by preparing and measuring identity information particles. By using the entanglement characteristics of the Bell state, the shared key negotiation was realized. Compared with other entangled states, the Bell state used in this protocol is easier to prepare, and the protocol only uses two quantum measurement operations, namely Z-based measurement and Bell measurement, which are easier to implement in existing technology. In addition, we proved that the proposed scheme can effectively resist participant attacks and external attacks, and that the protocol is equipped with a wavelength quantum filter and a photon number separator on both sides of Alice and Bob to avoid Trojan horse attacks. In the performance analysis of this protocol, the Cabello qubit efficiency was used to measure the performance of the quantum key agreement protocol. Results and Discussions First of all, in the previous research on quantum key agreement protocols, some scholars focus on how to simplify the quantum operation of participants, so as to better apply to the actual scene of resource scarcity, while others pay attention to how to prevent the man-in-the-middle attacks that may be encountered during the key agreement process and further improve the security of the protocol. The two-party mutual authentication semi-quantum key agreement protocol based on the Bell state proposed in this paper can not only reduce the requirements for participants capabilities and devices, but also realize mutual authentication between participants before key agreement to prevent the protocol from being attacked by man-in-the-middle. Finally, a security analysis shows that the protocol can effectively resist participant and external attacks. In addition, the performance analysis shows that the protocol can improve the quantum bit efficiency compared with some quantum key agreement protocols that meet a single function under the condition of satisfying two functional characteristics at the same time. Conclusions In this study, a two-party mutual authentication semi-quantum key agreement protocol based on the Bell state is proposed. The protocol not only ensures that the shared key can be fairly negotiated between the full quantum party, Alice, and the semi-quantum party, Bob, but more importantly, the two parties need to authenticate each other's identity before the key agreement, so as to resist external attackers posing as legitimate users to steal the shared key. Security analysis shows that this semi-quantum key agreement protocol can resist both participant and external attacks. Finally, through a performance analysis and comparison with existing quantum key agreement protocols, it is found that the protocol has certain advantages in terms of its function and performance.

车联网在生活中扮演着越来越重要的角色,它可以有效地防止交通拥堵从而减少交通事故.然而,在车联网中总是有非法车辆试图接入车联网并发布虚假消息.此外,现有方案多数存在计算效率低下的问题.针对上述存在的问题进行了研究,提出了一种车联网中基于雾计算和多TA的条件隐私保护认证方案.在保护车辆用户身份的条件下实现了车辆、雾节点、TA三者之间的身份认证,且在车辆追踪阶段可以还原车辆用户的真实身份,从而实现条件隐私保护.雾计算的使用降低了方案的计算和通信开销,同时多TA模型的使用也解决了单TA单点故障的问题.安全性证明和性能分析的结果表明该方案是安全且高效的.最后对当前方案进行了总结以及对未来研究作出了展望.

Objective Quantum cryptography is a new research field emerging from the combination of cryptography and quantum mechanics. Furthermore, the basic principles of quantum mechanics guarantee its security, such as Heisenberg's inaccuracy principle and the unclonability principle which are different from classical ciphers. Therefore, quantum cryptography is theoretically capable of achieving unconditional security. Recently, with the continuous development of quantum cryptography, its related research has received wide attention. Meanwhile, the quantum key agreement is an important branch of quantum cryptography and a quantum channel-based security protocol that calls for a secure shared key able to be negotiated between participants and does not allow any part of the participants to control the generation of this key. Unlike classical key agreement protocols relying on mathematical hard problems to guarantee security, the security of quantum key agreement protocols is guaranteed by the basic principles of quantum mechanics and can achieve unconditional security, thus better meeting practical needs. However, general quantum key agreement protocols can only satisfy the cases where all participants have full quantum capabilities. Thus, semi-quantum key agreements have been proposed by scholars, which means that one participant in the protocol has full quantum capability while the other participants have only semi-quantum capability. In this case, some of the large institutions or companies are treated as entities with full quantum capabilities, while some ordinary users are treated as entities with semi- quantum capabilities who only need to employ the Z-base {|0 >,|1 >} for quantum state preparation or measurement. However, there are still few studies on multi-party semi-quantum key agreement protocols, with cases of reliance on trusted third parties or low efficiency of quantum bits. Therefore, the multi-party semi-quantum key agreement protocol is significant to be studied. Methods We design a new four-party semi-quantum key protocol based on a four-particle cluster state. Furthermore, the secure shared key in this protocol is established by one full-quantum party of Dave, and three semi-quantum parties including Alice, Bob, and Charlie through measurement-resend operations and the entanglement properties of the four-particle cluster state, without the assistance of a trusted third party. The four-particle cluster state is a particular sort of four-particle entangled state whose entanglement properties are adopted in the key agreement and eavesdropping detection parts of the protocol. In this protocol, the measurement- resend operation is performed several times. Finally, since CTRL particles that are normally discarded in a previous protocol can be employed again, the quantum resource waste is reduced. In terms of security, the protocol is proven to be effective against internal attacks and all external attacks. Additionally, two optical devices, the wavelength quantum filter (WQF), and the photon number separator (PNS) are introduced in the protocol, which allows both Trojan horse attacks to be effectively defended against. In terms of qubit efficiency, the protocol performance is measured by Cabello qubit efficiency. Results and Discussions Firstly, general quantum key agreement protocols can achieve the purpose of shared keys securely established between participants. However, in the existing quantum key agreement protocols, participants are required to have excessive capabilities and equipment. Therefore, we put forward a new four-party semi- quantum key negotiation protocol based on a four- particle cluster state. The three semi-quantum participants of Alice, Bob, and Charlie, and one participant Dave with full quantum capability in this protocol can perform key negotiation without any third party. As a consequence, the requirements for participant capacity and equipment in this protocol are reduced. The four- particle cluster state is utilized in the protocol for key agreement and eavesdropping detection. Secondly, the measurement- resend operation is leveraged in the protocol, which means that the particle is randomly executed with a CTRL or SIFT operation. In this case, the CTRL operation means that the particle is subjected to a reflection operation, the SIFT operation means that the particle is subjected to a Z-base measurement with the preparation of a new particle, and finally the newly prepared particle is resent. Furthermore, the measurement-resend operation is performed twice in the protocol to make the CTRL particles normally discarded in the previous protocol can be reused, Therefore, the quantum resource waste is reduced. Thirdly, the protocol is verified to be effective against both external and internal attacks through security analysis. Meanwhile, the protocol shows superior performance through performance analysis. Conclusions Our paper proposes a four-party semi- quantum key agreement protocol based on a four-particle cluster state. In this protocol, no assistance from trusted third parties is required to ensure that a secure shared key is established by negotiation between a full quantum party and three semi-quantum parties and that the contributions of each party to the shared key are equal. Analysis indicates that internal attacks and all external attacks can be effectively defended by the new semi-quantum key agreement protocol. The final comparison results show that the proposed semi-quantum key agreement protocol can improve performance and save quantum resources simultaneously.

In order to further improve the privacy protection capability of the location privacy protection scheme of the Internet of Vehicles, a location privacy protection scheme supporting pseudonym updating is proposed based on the dynamic mix-zone. In this scheme, a trusted authority generates a pseudonym for the vehicle. When the age of the vehicle's pseudonym reaches the threshold, a dynamic mix-zone is established for pseudonym updating (generating or exchanging pseudonym). After the pseudonym updating, the vehicle performs message signature and authentication. The security analysis shows that the pseudonym updating scheme supports both location privacy protection and identity privacy protection. The simulation results show that compared with the existing mix-zone schemes, the scheme has higher average anonymous entropy and lower tracking rate, so it can achieve better location privacy protection function.

Objective In recent years, with the rapid development of e-commerce and computer, online shopping is more and more popular. In the meantime, the development of quantum algorithms makes the traditional e-payment protocols based on difficult mathematical problems more and more insecure, so the e-payment protocols based on quantum algorithms come into being. At present, most of the proposed quantum e-payment protocols use entangled states for quantum electronic signature protocols. However, the preparation and measurement of entangled states are very difficult, so in the case of ensuring the security of the protocols, using quantum states featuring more convenient preparation and measurement,instead of entangled states, has become a research direction of e-payment. Quantum walk is a technology that can produce the necessary entanglement resources spontaneously only by using the single-particle states without preparing entanglement resources in advance. This technology has been widely used in quantum computing and quantum simulation and is of certain practical value. At the same time, as people pay more attention to personal privacy, only users’ shopping lists being confidential to banks have been unable to meet people’s privacy needs. Therefore, in order to solve the above problems,we modify a classic e-payment agreement model and make the hidden users’ identity information not affect the normal delivery and merchants. Furthermore, we combine the quantum walk with quantum e-payment and propose a quantum epayment protocol to ensure that entanglement resources can be obtained without preparing entangled states in advance and guarantee that the buyers’ bank accounts and real identity information can be kept confidential to merchants.Methods Quantum walk is an extension of random walk in the quantum field. It takes the quantum as the carrier to simulate the chaotic nonlinear dynamic walk behavior. According to the characteristics of the quantum walk, the encrypted quantum communication channels are established accordingly. The quantum walk mainly contains the complex Hilbert space of two main quantum spaces, namely, coin space and position space. The protocol is based on the one-dimensional quantum walk teleportation, and through the two-step quantum walk, the shift operator can make the position space and coin space entangle with each other, so as to construct quantum channels for information transmission. The biggest advantage of quantum walk technology is that it can obtain the entanglement resources through the single photon operation. The measurement and preparation of the protocol are simpler compared with directly operating entangled states, and the randomness of the quantum walk makes the transmission more secure. In addition, by dividing the shopping information of buyers into the identity information accessible to the banks and making the shopping list open to the merchants, the banks and the merchants in the protocol will not know the information obtained by the other party so that the privacy of the buyers is greatly protected.Results and Discussions Firstly, in order to further protect the users’ privacy, we modify a classic electronic payment agreement model（Fig. 1）. In this model, we reduce the workload of buyers and give the processing and distribution of information to third-party platforms. While keeping the buyers’ shopping lists confidential to the banks, the buyers’ identity information is also unavailable to the merchants. So this protocol makes the merchants and the banks only have the information that they need and know nothing of the information obtained by the other party. Secondly, quantum walk technology is applied to various stages of the protocol including the trading purchase phase, trading payment phase, and verifying phase（Fig. 2）. By applying quantum walk technology, the complexity of quantum resource preparation and measurement in the protocol is reduced. Finally, the security analysis of this protocol is conducted（Fig. 3）, and the result shows that neither the internal nor external attackers of this protocol can obtain the secret information in the protocol, and this protocol can resist both internal and external attacks.Conclusions This protocol, compared with the existing quantum e-payment protocols, not only retains the third-party platforms and the inter-bank payment function but also combines the quantum walk and electronic payment. It makes the participants of the protocol in the initial stage free from preparing particles in entangled states and makes them only prepare the single-particle states which can get the required entanglement resources. This move reduces the complexity of quantum state preparation and measurement. At the same time, the shopping information of the buyers is divided, with the information of the purchased goods confidential to the banks and the buyers’ private information unavailable to the merchants. In addition, when the merchants really need this part of the information of the buyers, they can apply to thirdparty platforms for the information. Being reviewed by the platforms and approved by the buyers, the merchants can know the information they want, so as to complete the corresponding operation. Finally, security analysis shows that this protocol can resist internal and external attacks and is safe and feasible under current technology.

Owing to the unique properties of quantum mechanics, the quantum key agreement has unconditional security in theory. In this paper, a quantum key agreement protocol is designed. The four-particle cluster states are used as quantum sources. Two communication parties conduct joint Bell measurements respectively, and code through the controlled NOT gate and Hadamard gate to achieve shared secret. Here, weak measurement and quantum measurement reversal methods are used to deal with decoherence during transmission. The proposed key agreement protocol not only has the ability to respond to various participant and external attacks but also has higher communication efficiency.

The controlled quantum key agreement(CQKA)protocol requires a controller to oversee the process of all participants negotiating a key,which can satisfy the needs of certain specific scenarios.Existing CQKA protocols are mostly two-party or three-party,and they do not entirely meet the actual needs.To address this problem,this paper proposes new CQKA protocols based on Bell states and Bell measurements.The new CQKA protocols can be successfully implemented for any N-party,not just two-party.Furthermore,the security and efficiency analyses demonstrate that the new CQKA protocols are not only secure but also more efficient in terms of quantum bit.

Objective With the continuous development of quantum calculations, the classic cryptosystem that relies on mathematical difficulties and computational complexity to ensure security is constantly under threat. Therefore, in recent years, a large number of scholars have attracted attention from the quantum cryptography produced by the combination of cryptography and quantum mechanics. At present, quantum cryptography has many branches, such as quantum key distribution, quantum key agreement, quantum secure sharing, quantum secure direct communication, and deterministic secure quantum communication. Among them, quantum key agreement is an important branch of quantum cryptography. In real life, quantum key agreement is widely used in scenarios such as end-to-end communication and internet of things. Although, in the current quantum key agreement protocol, a secure shared key can be established between legal participants. However, participants in the quantum key agreement protocol are required to have high capabilities and equipment. But, the quantum equipment is still too expensive even in relatively rich future material conditions. In order to cope with this situation, the semi-quantum key agreement protocol is proposed by scholars. It allows one or more participants in the protocol to only have simple quantum capabilities, that is, to use the Z basis (0), 1)) for preparation and measurement. Therefore, the protocol reduces the requirements for participant capabilities and equipment. In addition, research on semi-quantum key agreement is relatively small. Therefore, the semi-quantum key agreement needs to be studied by scholars. Methods In this paper, a new two-party semi-quantum key agreement protocol is designed based on the G-like state. The securely shared key in the protocol is established by the two classical parties, Alice and Bob, through the measurement-resending operation and the entanglement characteristics of the G-like state with the assistance of a trusted third party with full quantum capabilities, Charlie, and the contributions of both parties are equal. The shared key cannot be determined by any participants alone. The G-like state is a special three-particle entangled state, and its entanglement properties are used in the key agreement and eavesdropping detection part of the protocol. For example, the measurement result of the counterpart can be inferred by the participant through the entanglement properties of his own initial quantum state and the G-like state. And the measurement-resending operation means that the particles are randomly executed the CTRL and SIFT operations. Among them, the CTRL operation means that the particles are only executed to reflection operations, and the SIFT operation means that the particles are executed to the Z basic measurement and a new particle is prepared. Finally, the newly prepared particles are resent. In this protocol, the measurement-resending operation is performed twice by us. Therefore, the CTRL particles usually discarded in the previous protocol can be reused and the waste of quantum resources is reduced. In terms of security, the security of the protocol is guaranteed by the entanglement characteristics of the G-like state. In addition, two optical devices, wavelength quantum filter (WQF) and photon number separator (PNS), have been introduced, so that the protocol can also resist two Trojan horse attacks. In terms of qubit efficiency, the performance of the protocol is measured by Cabello qubit efficiency. Results and Discussions Although most of the quantum key agreement protocols have been proposed to enable the secure keys to be established between participants. But all participants in these protocols are required to have full quantum capabilities. However, quantum devices are relatively expensive and difficult to carry. Therefore, the semi-quantum key agreement protocol is proposed to solve this problem. A trusted third party with full quantum capabilities is introduced, and thus the two-party semi-quantum key agreement protocol can be realized. The trusted third party can be used to prepare the G-like state required for this protocol. At the same time, it can also perform eavesdropping detection jointly with all participants. This ensures that the external attacks can be well resisted by the protocol, and in addition, the participant attacks can also be well resisted by the protocol. Since the quantum state in this protocol has been transmitted for many times, the attacker can eavesdrop on the information related to the shared key through a Trojan horse attack. Therefore, two optical devices, the wavelength quantum filter and the photon number separator, are introduced by us. Among them, the invisible photons can be filtered out by the wavelength quantum filter, and the delayed photons can be detected by the photon number separator. This ensures that the protocol can also resist two types of Trojan attacks. In terms of performance, Cabello qubit efficiency is used to measure the performance of the protocol. At present, this method is mainly used to evaluate the performance of the quantum key agreement protocol. The qubit efficiency of the semi-quantum key agreement protocol is generally low. But this kind of agreement has low requirements for participants. Therefore, the semi-quantum key agreement protocol is more suitable for our current situation. Conclusions In this paper, a two-party semi-quantum key agreement protocol based on G-like state is proposed. A securely shared key can be established by two semi-quantum parties with the assistance of a trusted third party. In terms of security, participant attacks and external attacks can be well resisted. In addition, the protocol also has an advantage in performance.

Based on single-particle states and four-particle GHZ states, a mutual authentication quantum key agreement protocol is proposed. The quantum key agreement protocol can not only establish shared keys fairly, but also authenticate participants' identities before negotiating keys. In order to mutually authenticate each other's identity, the verifier can identify the identity of the prover according to whether the prover can choose the correct measurement bases with the hash values of their shared secret identity information and the random number. In key agreement stage, two parties can fairly establish a shared key by using the measurement correlation property of four-particle GHZ states. The shared key involves the partial keys of two participants, their identity information and the values of two random numbers. Although the hash functions are used in both the mutual authentication stage and the key agreement stage, the new quantum key agreement protocol is still proved to be unconditionally secure. Moreover, it has flexible qubit efficiency and can achieve high qubit efficiency.

A mutual authentication quantum key agreement protocol can authenticate participants’ identities before establishing shared keys fairly. Therefore, it is more in line with the actual demand than the general quantum key agreement protocols. With Bell states and their entanglement exchange relations, a new mutual authentication quantum key agreement protocol is proposed. The participants can mutually authenticate each other’s identity by using their secret identity information and the measurement correlation property of Bell states. Moreover, they can negotiate session keys fairly with the entanglement exchange relations of Bell states. The new mutual authentication quantum key agreement protocol is proved to be unconditionally secure and has good performance.

In view of the security and practicability requirements of an electronic payment system as well as the problems of complicated steps and trivial signature processes and others in the traditional electronic payment protocol based on controlled teleportation, we propose an electronic payment protocol based on quantum dense coding. The proposed protocol uses quantum operations such as quantum key distribution, single particle measurement, Bell measurement, and unitary operator to perform message blinding, authorization, signature and verification processes in order, and thus completes the whole electronic payment process. In the new protocol, the three-particle entangled state is used as the quantum channel, which can use less resources to complete transactions among different banks. Moreover, by using dense coding instead of controlled teleportation, it is possible to transmit two-bit classical messages with only one qubit. The security analysis shows that the protocol can guarantee the blindness of the purchase information, and satisfy the undeniability, unforgeability and unconditional security.

The measurement device independent quantum key distribution (MDI-QKD) system can resist any attacks on the side channel of the single-photon detector. In order to further optimize the multi-party MDI-QKD protocol, this paper investigates the multi-party MDI-QKD protocol hosed on W states, and introduces the detector quality factor (ratio of dark coun Y-0 to detection efficiency eta(d)) as an analog parameter to simulate and analyze the factors influencing hit error rate and key generation rate. The simulation results show that the increase of any one among the three variables of channel-transmission loss, fiber-channel distance and detector quality factor enhances the hit error rate and reduces the key generation rate.

In order to eliminate the influence of the channel noise, two new measurement-device-independent quantum key distribution (MDI-QKD) protocols are proposed with logical quantum states. They can resist collective-dephasing noise and collective-rotation noise, respectively. This paper produces logical quantum states by adding the auxiliary light sources, the CNOT operations and the Hadamard transforms in the system model. The main light sources and auxiliary light sources are flexible and easily implemented, since they can be weak coherent state (WCS) sources, heralded single-photon sources (HSPSs) or heralded pair coherent state (HPCS) sources. To generate one key bit, the new MDI-QKD protocols only need one logical qubit with two particles so that they have high qubit efficiency. Moreover, the new protocols also use partial Bell-state measurement (BSM) which is very easily implemented with existing technologies.

This paper studies a measurement-device-independent quantum key distribution protocol based on a multiple crystal heralded source and pulse position modulation to improve its performance. The performances of the protocols with or without pulse position modulation are compared under the multiple crystal heralded source. The simulation results show that the application of pulse position modulation can further improve the key generation rate and increase secure transmission distance of the protocol. Moreover, as the time slot increases, the key generation rate and the secure transmission distance gradually rise. Furthermore, we analyze the relationship between the secure transmission distance and the key generation rate under different detection efficiencies of the detector. The results show that the higher detection efficiency of the detector leads to the greater key generation rate and the longer secure transmission distance.

In order to analyze the measurement-device-independent quantum key distribution protocol more comprehensively, the statistical fluctuation analysis of measurement -device-independent quantum key distribution protocols based on heralded pair coherent state is carried out. First, with the increase of the number of transmitted signal pulses in the statistical fluctuation of light source, the relationships of bit error rate and key generation rate with transmission distance arc analyzed. The results show that increasing the number of pulses can improve the key generation rate and the maximum transmission distance, and can reduce the bit error rate. Moreover, the measurement-device-independent quantum key distribution protocol based on heralded pair coherent state has better performance than the one based on heralded single photon sources. When the light source is statistical fluctuating, the relationship between the key generation rate and the transmission distance of measurement-device-independent quantum key distribution protocol based on heralded pair coherent state in asymmetric channels is further analyzed, and the simulation results show that this protocol in asymmetric channels has better performance than that in symmetric channels.

With heralded pair coherent states (HPCS), orbital angular momentum (OAM) states and pulse position modulation (PPM) technology, a decoy-state measurement-device-independent quantum key distribution (MDI-QKD) protocol is proposed. OAM states and PPM technology are used to realize the coding of the signal states in the HPCS light source. The use of HPCS light source, OAM coding and PPM coding cannot only reduce the error rate but also improve the key generation rate and communication distance. The new MDI-QKD protocol also employs three-intensity decoy states to avoid the attacks against the light source. By calculating the error rate and key generation rate, the performance of the MDI-QKD protocol is analyzed. Numerical simulation shows that the protocol has very low error rate and very high key generation rate. Moreover, the maximum communication distance can reach 455 km.