Quantum Communication Networks and Trust Management: A Survey

This paper summarizes the state of art in quantum communication networks and trust management in recent years. As in the classical networks, trust management is the premise and foundation of quantum secure communication and cannot simply be attributed to security issues, therefore the basic and importance of trust management in quantum communication networks should be taken more seriously. Compared with other theories and techniques in quantum communication, the trust of quantum communication and trust management model in quantum communication network environment is still in its initial stage. In this paper, the core technologies of establishing secure and reliable quantum communication networks are categorized and summarized, and the trends of each direction in trust management of quantum communication network are discussed in depth.

; Masanes, Renner, Christandl et al. (2014); Bacco, Christensen, Castaneda et al. (2016); Roberts, Lucamarini, Dynes et al. (2017); Pereira and Pirandola (2018)], in which the safety is independent with equipment parameters, security is not guaranteed by the fundamental principles of quantum mechanics, but rather than the nonsignal theorem based on the theory of relativity. The biggest advantage of device independent QKD is that even if the quantum mechanics is not established, it can still provide unconditional secure key distribution.

Quantum teleportation (QT)
Quantum teleportation, as one of the important fields in research of quantum communication, plays an important role in the field of quantum computation and quantum communication. In 1993, six scientists from Bennett and other 4 countries put forward the first quantum teleportation scheme [Bennett, Brassard and Crépeau (1993)], which ushered a new era of quantum teleportation. In 1994, Davidovich et al. proposed a quantum state transfer scheme based on Bell basis measurement [Davidovich, Zagury, Brune et al. (1994)]. In 1997, Guo's team proposed quantum teleportation scheme based on quantum cavity electrodynamics [Zheng and Guo (1997)]. For the first time, a research group in Austria successfully demonstrated the quantum teleportation experimentally (The results have made a stir in the international academic circles) [Nielsen, Knill and Laflamme (1998)]. In 2000, the Photoelectric Institute of Shanxi University proposed a quantum teleportation scheme by using bright squeezed light. Li et al. presented a probabilistic teleportation scheme for single particle quantum states theoretically [Li, Li and Guo (2000)]. In 2001, Shih's team in University of Maryland successfully achieved quantum teleportation experiments using nonlinear methods [Kim, Kulik and Shih (2001)]. In 2002, Guo's team realized the teleportation of three particle entangled W states by using non-maximally entangled state as quantum channel [Zheng, Gu and Guo (2002)]. In 2003, Roa et al. proposed a teleportation scheme for d dimensional quantum system [Roa and Dolgado (2003)]. In 2005, Pan's team created a world record of two-way quantum entanglement distribution with 13 km in Hefei [Peng, Yang, Bao et al. (2005)]. In 2012, Pan's team achieved the hundred kilometers quantum teleportation and entanglement distribution in free space for the first time in the world, which laid technical foundation for launching the first quantum communication satellite [Yin, Ren, Lu et al. (2012)]. In the same year, the scientists at University of Vienna and Austria Academy of sciences realized the most distant teleportation of a quantum state (143 Km) [Ma, Herbst, Scheidl et al. (2012)]. In recent years, quantum teleportation has attracted a large number of scholars, and some effective quantum teleportation schemes have been proposed [Ye and Lin (2013); Knoll, Schmiegelow and Larotonda (2013); Pfaff, Hensen, Bernien et al. (2014); Pirandola, Eisert, Weedbrook et al. (2015); Yang, Ma, Zheng et al. (2017) ;Huo, Qin, Cheng et al. (2018)], which have promoted the development of quantum communication.

Quantum secret sharing (QSS)
Secret sharing is an important branch of cryptography. Quantum secret sharing (QSS) is the quantum generalization of classical secret sharing. QSS is realized based on quantum mechanics rather than mathematical problems or computational complexity, so it is more secure. Since 1999, Hillery et al. first proposed a QSS protocol based on multi-particle entanglement [Lucamarini and Mancini (2005)]. A high dimensional QSDC protocol based on dense coding was proposed by Wang et al. [Wang, Deng, Li et al. (2005)]. In 2006, Lee et al. proposed a QSDC protocol with authentication function [Lee, Lim and Yang (2005)], which can prevent active attacks effectively. In 2008, Liu et al. proposed a more efficient QSDC protocol based on authentication [Liu, Chen, Li et al. (2008)]. In 2010, Liu et al. also put forward a QSDC protocol based on authentication [Liu, Pei, Quan et al. (2010)]. In 2011, Wu et al. put forward another QSDC scheme based on entangled states [Wu, Zhai, Cao et al. (2011)]. In 2013, Chang et al. proposed a QSDC and authentication protocol using single photons [Chang, Xu, Zhang et al. (2013)]. In 2014, Yuan et al. proposed a deterministic secure quantum communication (DSQC) scheme by using GHZ states [Yuan, Zhang, Hong et al. (2014)]. In 2015, Li et al. proposed controlled quantum secure direct communication (CQSDC) protocol based on five atom cluster states using cavity quantum electrodynamics [Li, Li and Nie (2015)]. In 2017, Bai et al. propsoed quantum secret sharing by using orthogonal multiqubit entangled states [Bai, Li, Liu et al. (2017)]. In 2018, Qin et al. propsoed multiparty to multiparty quantum secret sharing ]. In fact, QSDC is one of the main research branches of quantum communication system. It has received extensive attention in recent years because it transmits secure information directly without generating quantum key first. However, the research of QSDC is mainly focused on the design of QSDC protocol, and most protocols designed are in ideal environment. Obviously, the research of QSDC has a certain distance from the practical.

Quantum identity authentication (QIA)
To realize secure quantum communication, identity authentication is also very important. Since the classical authentication method is not unconditional secure, it cannot effectively prevent the attacker to pretend to be a legitimate correspondent. If the attacker controls the quantum channel and classical channel, he can succeed in middle-man attack. Therefore, identity authentication between the two sides in one communication is imperative. In recent years, researchers have proposed a variety of quantum identity authentication (QIA) schemes. In 1999, Duek et al. put forward a secure QIA system, which combining the classic authentication process with the quantum key distribution [Dusek, Haderka, Hendrych et al. (1999)]. In 2000, Ljunggren et al. achieved the purpose of certification by inserting the quantum sequence generated by shared information previously in particles of BB84 protocol [Ljunggren, Bourennane and Karlsson (2000)].
In 2001, Gurty et al. proposed a QIA scheme, in which Bob verified the identity of Alice with the help of Trent by operating three particle entangled states [Gurty and Santors (2012)]. In 2002, Mihara presented three QIA schemes based on entanglement and unitary operations [Mihara (2002)]. In 2003, Zeng et al. proposed that the encoded measurement basis based on shared information previously can be used to verify the identities between two sides, and the entangled states can be used to ensure the security of information transmitted [Zeng and Zhang (2001) ;Zhou, Zeng, Zeng et al. (2005)]. In 2006, Zhang et al. proposed a one-way QIA scheme based on ping-pong protocol and quantum controlled not gate [Zhang, Zeng, Zhou et al. (2006)]. In 2008 and 2009, Yang et al. put forward two multi-party simultaneous QIA protocols based on single photons ] and GHZ states [Yang and Wen (2009) [Gao, Qin, Guo et al. (2011)]. In 2013, Yang et al. proposed a QIA protocol with quantum (t, n) threshold based on GHZ states [Yang, Wang, Jia et al. (2013)]. In 2014, Yuan et al. put forward a QIA scheme based on non-entanglement "Ping-Pong" technology [Yuan, Liu, Pan et al. (2014)]. In 2015, Zhandry et al. proposed a secure authentication scheme based on encryption in the quantum random oracle model [Zhandry (2012)]. In 2016, Ma et al. proposed continuous-variable quantum identity authentication based on quantum teleportation [Ma, Huang, Bao et al. (2016)]. In 2019, Zawadzki proposed quantum identity authentication without entanglement [Zawadzki (2019)]. From the analyses made above, we know that quantum identity authentication plays an important role in quantum communication network. How to achieve efficient user identity authentication in large scale networks is a hot topic. At present, most quantum identity authentication is still a point to point authentication, which is low efficiency and lead to waste of classical and quantum resources. We are also pleased to see that some scholars also paid close attention to these problems and put forward multi-party quantum identity authentication protocols.

Quantum Signature (QS)
Most of the traditional digital signature algorithms are based on the assumption of not been proved computation complexity, for example, the difficulty of large integer factorization and discrete logarithm problem solving. However, the quantum algorithm can decompose large integer and solve discrete logarithm in polynomial time [Shor (1994)]. As a result, most of the current digital signature schemes will fail if the quantum computer is successfully applied. Therefore, the design of quantum signature (QS) algorithm which can resist the attack of quantum computer is a hot topic. In recent years, signature based on quantum mechanics has achieved a lot of results. In 2001, Zeng et al. proposed the first arbitration QS scheme based on symmetric cryptosystem [Zeng, Ma, Wang et al. (2011)]. Gottesman et al. also proposed a real QS scheme based on quantum one-way function in the same year [Gottesman and Chuang (2001)]. In 2002, Zeng et al. put forward an arbitration QS scheme with appendix by using the relevance between quantum one-time pad and GHZ state [Zeng and Keitel (2002)], and further improved the scheme in 2007 [Zeng (2008)]. In 2004, Lee et al. proposed two arbitration QS scheme with message recovery [Lee, Hong, Hyunsang et al. (2004)]. However, because entanglement is not used in this scheme, GHZ state can be replaced with the classical correlation state. In 2005, Lü et al. proposed an arbitration QS scheme based on quantum one-way function [Lü and Feng (2005)], which realized the signature of unknown quantum state. In 2006, Wang et al. proposed a new arbitration QS scheme with message recovery based on quantum one-time pad and quantum key distribution [Wang, Zhang and Tang (2006)], in which particles are measured with von Neumann method and entangled states are not needed. In 2007, Wang et al. put forward an arbitration QS protocol with appendix by using the hash function, which realizes the message signature of any bit [Wang, Zhang and Tang (2008)]. In 2008, Yang et al. proposed a multi-proxy quantum group signature scheme with threshold shared verification [Yang (2008)]. In 2010, Wen et al. presented a quantum group signature scheme based on quantum teleportation [Wen, Tian, Ji et al. (2010)]. In 2011, Xu et al. proposed a quantum blind signature scheme for a distributed electronic voting system based on the properties of group signature and blind signature [Xu, Huang, Yang et al. (2011)]. In 2012, Yin et al. put forward a blind signature scheme based on χ-type states [Yin, Ma, Liu et al. (2012)]. In 2013, Wen et al. proposed an electronic payment scheme among banks based on quantum proxy blind signature [Wen, Chen and Fang (2013)]. In 2014, Yu et al. proposed a reusable quantum signature scheme [Yu, Guo and Lin (2014)]. In 2015, Wang et al. introduced a quantum proxy group signature scheme based on five particle cluster states [Wang, Ma, Wang et al. (2015)]. In 2016, Luo et al. proposed a quantum homomorphic signature based on bell-state measurement [Luo, Yang, She et al. (2016)]. In 2018, Qin et al. put forward a batch quantum multi-proxy signature ]. In summary, there are many achievements in quantum signature, including arbitration quantum signature, quantum group signature, quantum blind signature, and other special quantum signature scheme. Although many schemes are based on the same principle, quantum signature is bound to usher in new applications with the development of quantum communication and quantum communication network.

Quantum Bit Commitment (QBC)
Although there exist bit commitment protocols with unconditionally hiding and calculated binding, or protocols with calculated hiding and unconditionally binding [Naor, Ostrovsky, Venkatesan et al. (1998)], classical bit commitment protocols with known unconditional security are not possible. In the research of traditional bit commitment, the researchers achieved computationally secure commitment protocol based on some oneway functions or mathematical problems. Since unconditional secure QKD protocol appears, some scholars turned to research on quantum bit commitment (QBC). They hoped that QBC can provide unconditional security. In 1990s, Scholars put forward some QBC protocols [Brassard and Crépeau (1991) ;Brassard, Crdpeau, Jozsa et al. (1993); Ardehafi (1995); Mayers (1996); Lo and Chau (1997)], one of the most famous is the QBC protocol (BCJL protocol [Brassard, Crdpeau, Jozsa et al. (1993)]) proposed by Brassard et al. [Ardehafi (1995)], which was claimed unconditionally secure at that time. However, Mayers proved that the BCJL protocol is not secure [Mayers (1996)]. In 1997, Lo et al. proved that the previous QBC protocol does not have unconditional security [Lo and Chau (1997)]. And almost at the same time, Mayers also proved that the general QBC protocol (including classical measurement and two-way communication) cannot be unconditional secure [Mayers (1997)]. The non-existence theorem of unconditional secure QBC (i.e., Mayers-Lo-Chau no-go theorem) is often referred to as the "regression" of quantum cryptography research. If based on a certain assumption, or limited to specific circumstances, or put a low security requirement, secure QBC will become possible, so the study of QBC has not been suspended because of the Mayers-Lo-Chau no-go theorem. In 1998, Salvail presented a secure QBC protocol based on the assumption that the sender Alice cannot perform joint measurement on n qubits [Salvail (1998)]. In 1999 and 2005, Kent introduced two bits commitment protocols to resist the attacks of quantum computer based on special relativity (RBC1 protocol [Kent (1999)] and RBC2 protocol [Kent (2005)]). In 2004, Hardy et al. presented an unconditionally secure QBC protocol with deception sensitivity [Hardy and Kent (2004)]. In this protocol, if the committed or promised party is trying to cheat, the other party can detect such deceptive behavior by non-zero probability. Damgard et al. proposed [Song and Yang (2018)]. As the basis of designing many other quantum secure protocols, such as quantum coin flipping protocol and secure multi-party quantum computation, QBC protocol plays an important role in quantum secure communication, which will be a hot spot in this field.

Quantum coin tossing (QCT)
The coin tossing protocol is one of the basic cryptographic primitives, and it establishes a random bit between two users which are isolated in space and distrust mutually. In 1981, Blum proposed the first coin tossing protocol by using the classic password [Blum (1981)]. In 1984, Bennett et al. extended the idea of throwing coins into the quantum field, and proposed a quantum coin tossing protocol known as the "BB84 protocol" [Aharonov, Ta-Shma, Vazirani et al. (2000)], which is different from the "BB84" protocol in QKD. In the next 10 years, the development of quantum coin tossing is relatively slow, the main reason is that the quantum coin tossing faces this controversy: Whether quantum coin tossing has unconditional security just like QKD? Until 1997, Mayers proved mathematically that the perfect quantum bit commitment (equivalent to quantum coin tossing) does not exist [Mayers (1997)], quantum coin tossing got the attention of researchers gradually. In 1998, Lo et al. gave the security proof of nonexisting absolute secure coin tossing protocol [Lo and Chau (1997)], but at the same time they also pointed out that the quantum coin tossing is still more secure than the classic one. This is why the researchers did not break the study of quantum coin tossing. In 2000, Aharonov et al. took the "BB84 protocol" as a template, and proposed a quantum coin tossing protocol based on quantum bit contract protocol (ATVY protocol) [Aharonov, Ta-Shma, Vazirani et al. (2000)], in which the preference probability was 0.354. In 2004, Ambainis designed a quantum coin tossing protocol based on the multi-band quantum symbols [Ambainis (2004)], in which the preference probability was reduced to 0.25. In the same year, Ambainis et al. proposed a multi-party quantum coin tossing protocol [Ambainis, Buhrman, Dodis et al. (2004)]. In 2005, Mochon designed a new quantum coin tossing protocol, in which the preference probability was reduced to 0.192 [Mochon (2005)]. In 2007, Kitaev et al. proved that the preference probability of quantum coin tossing can be reduced to 0.21 by using semi linear programming theory [Kitaev and Witte (2007) With the development of quantum communication and network, we believe that the quantum coin toss protocol will have broad applications in the near future.

Quantum oblivious transfer (QOT)
As an important basis of quantum secure two-party computations, quantum oblivious transfer (QOT) has received much attention. In 1992, Yao et al. proposed a QOT protocol based on quantum bit commitment [Bennett, Brasssard, Crépeau et al. (1991)]. In 2006, He et al. proposed a quantum secret all-or-non oblivious transfer protocol based on quantum entanglement [He and Wang (2003)]. The security proof is given and the non-equivalence(?) of quantum secret all-or-non oblivious transfer protocol and quantum two-take-one oblivious transfer protocol is proved [He and Wang (2006)]. In 2007, Colbeck et al. further studied the five conditions security of the two-party classic calculation, which showed that there was no unconditional secure classical calculation and illustrated the transmission results through quantum oblivious transfer [Colbeck (2007)]. In the same year, Huang et al. put forward a QOT protocol by using the quantum positive operator [Yang, Huang, Yao et al. (2007)]. In addition, some scholars studied quantum oblivious transfer in theory [Chen, Huang, Li et al. (2008)

Secure multi-party quantum computation (SMQC)
Secure multi-party computation (SMC) is the theoretical basis of distributed cryptography and also a key problem in distributed computing. Since 1982, Yao (Turing Award winner) proposed secure multi-party computation [Yao (1982)], which has attracted much attention now. At present, SMC based on mathematical complexity has made great progress in theory and application. However, these methods are based on the computational complexity and are computationally secure. With the rapid development of quantum information technology, the security of classical cryptography algorithm based on complexity theory has been seriously challenged. Secure quantum multiparty computation is a new hotspot, which combines quantum information technology and SMC. In 2002, Crépeau et al. proposed the concept of SMQC and studied it systematically [Crépeau, Gottesam and Smith (2002)]. Crépeau not only extended the classical SMC problem to SMQC, but also constructed a SMQC protocol based on quantum secret sharing protocol, which can tolerate any t (<n/6) trickers. In 2006, Ben-Or et al. proposed a verifiable SMQC scheme based on approximate quantum error correction codes and quantum authentication schemes [Ben-Or, Crépeau, Gottesman et al. (2006)], which can tolerate [(n-1)/2] trickers. However, there are still some problems in these schemes. First, each participant must own a quantum state, however, it is not easy to be applied in practice because of the quantum coherence. Second, these SMQC schemes are only applicable to static fraud, and not to the case of adaptive fraud, for example they should determine which participants are not honest prior to the start of the protocol, which does not apply to the actual application of the dynamic changes of frauds. Finally, the SMQC protocol given by Crépeau et al. is just a few formal definitions, which defined the quantum security calculation with trusted third party in the ideal environment. However, in practical applications, the trusted third party does not virtually exist. Therefore, it is not efficient to implement secure multi-party quantum computation for special applications. In spite of this, some scholars have been concerned about this in recent years. In 2010, Loukopoulos et al. proposed a SMQC scheme in a dishonest environment by using quantum entanglement [Loukopoulos and Browne (2010)], which can tolerate [n/2] trickers. In 2013, Li et al. improved the SMQC protocol, which improves the efficiency of protocol [Li, Wen, Qin et al. (2013)]. According to the analyses made above, the research focused on the characteristics of basic SMQC protocol still has a certain distance from the practical application. To solve these problems, some SMQC protocols for special applications have been proposed, such as quantum anonymous communication protocol [Wang, Wen and Zhu (2010)], blind quantum computing protocol [Broadbent, Fitzsimons and Kashefi (2009) ;Shi, Mu, Zhong et al. (2016)], quantum voting protocol [Li and Zeng (2008)] and quantum auction protocol [Hogg, Harsha and Chen (2007)]. Compared with the classical SMC, due to the unique characteristics of quantum information, SMQC shows great advantages in security, robustness and communication efficiency, especially in eavesdropping detection.

Research on quantum communication network
Since the mode of point-to-point quantum communication cannot meet the requirements of practical application. Quantum communication network is proposed to provide secure communication services for more users with limited resources, and the global wide area quantum communication network is in research at present. In 2002, the United States began to design DARPA quantum key distribution network, and built a six-node quantum network [Elliott, Colvin, Pearson et al. (2005)

Research of trust management in quantum communication network
To make quantum communication and quantum communication network practical, to expand the application and improve the distance of quantum communication, it is urgent to establish a secure and reliable quantum communication network to meet the needs of multi-user communication. Fig. 3 is the structure diagram of quantum communication network with trusted third party (TTP). In Fig. 3, we assume that node 3 u wants to communicate with node 1 u , but 3 u does not know whether 1 u is credible or not. To prevent himself from being cheated by 1 u , 3 u gets some information which can evaluate the trust degree of 1 u from TTP. Then 3 u calculates the trust value of 1 u according to the information provided by TTP. 3 u judges whether 1 u is credible according to the trust value he calculated. Like classical networks, trust problem is the premise and foundation of quantum secure communication and trust cannot simply be attributed to security issues, the basic and importance of trust management in quantum communication networks should be seen. How to ensure the reliability of each node (user) in the quantum communication network and prevent counterfeiting, tampering, hacking, denial and deception, is the key to ensure the practical and network of quantum communication. Therefore, the research of quantum trust management model in the quantum communication network will become a hotspot. Although some scholars have concerned about the trust of quantum communication and trust management model in the quantum communication network environment, however, compared with other theories and techniques of quantum communication, the results of trust and trust management model of quantum communication are very few, which is still in its initial stage. At present, the existing results mainly involves trust modeling (quantitative description of each trust factor), trust establishment (assessment), node behavior management, multi-user quantum secure communication and secret information sharing.

Trust management modeling in quantum communication network
The results about quantum trust modeling is few. Liu et al. [Liu and Li (2012)] proposed a quantum trust management model based on social network. Zhou [Zhou (2012) In previous studies, they are found that the quantum communication network is similar with the classical communication network: there are many factors that are related to node trust in quantum communication networks, such as the historical reputation of nodes, the probability of a one-time success in quantum communication, the identity of node, the location of the node. These trust factors have the characteristics of randomness, subjectivity and diversity, which are mainly fuzzy. The main difficulty in study of trust lies in how to make a quantitative and accurate description of fuzziness.

The evaluation of trust in quantum communication network environment
About the evaluation of trust, the results are mainly focused on quantum identity authentication (In fact, two sides in one communication have established some trust between each other after the identity authentication), quantum bit commitment and trust evaluation (to decide whether a node is trustable or not by evaluating the trust degree of the node). In the study of quantum identity authentication, a (T, n) threshold authentication scheme based on GHZ was put forward in Yang et al. [Yang, Wang, Jia et al. (2013)]. A quantum identity authentication scheme without entanglement was studied based on the "ping pong" technique in Yuan et al. [Yuan, Liu, Pan et al. (2014)]. About the study of quantum bit commitment, Lunghi et al. [Lunghi, Kaniewski, Bussières et al. (2013)] studied the quantum bit commitment experiment based on quantum communication and special relativity, which established trust directly between the two parties, Liu et al. [Liu, Cao, Curty et al. (2014)] achieved a unconditional secure "bit commitment" experiment, and solved the problem of how to establish trust between distrustful terminals, which was a major breakthrough and was evaluated as an important progress in cryptography and a pioneer in experiment in this field. As for the study of quantum trust evaluation, Zhou et al. [Zhou (2012); Liu and Li (2012)] characterized the degree of trust between nodes by using the communication quality (the one-time success probability of quantum communication among nodes), based on which the trust of node was evaluated. Zhang et al. [Zhang, Xie, Yin et al. (2017)] discussed how to improve the security of information transferring between trusted nodes by studying the trusted node model. However, Yang et al. [Yang, Wang, Jia et al. (2013); Yuan, Liu, Pan et al. (2014); Zhandry (2012); Ma, Huang, Bao et al. (2016); Zawadzki (2019); Lunghi, Kaniewski, Bussières et al. (2013);Liu, Cao, Curty et al. (2014)] established trust directly between the two parties by using quantum identity authentication and quantum bit commitment, trust in multi-user environment was not taken into account. Zhou et al. [Zhou (2012); Liu and Li (2012);Pattaranantakul, Sanguannam, Sangwongngam et al. (2015); Peter and Stefan (2009)] evaluated the node trust only with the one-time success probability of quantum communication (or decide whether to establish a trust between nodes), how to safely evaluate the trust in multi-user environment was not considered. Furthermore, multiple factors were not considered that affect the trust of nodes, such as the historical reputation degree of nodes, the probability of successful communication, the identity information of nodes and the location of nodes.

The problem of node behavior management in quantum communication network
The results about node behavior management in quantum communication networks are few. Zhou et al. [Zhou (2012); Liu and Li (2012); Pattaranantakul, Sanguannam, Sangwongngam et al. (2015)] studied the behavior of quantum nodes by measuring whether the nodes achieving the desired requirements (such as the one-time success probability of a node). You et al. [You, Liu and Wang (2012)] proposed a optimization model of network resource allocation based on quantum behavior. However, in Zhou et al. [Zhou (2012); Liu and Li (2012); Pattaranantakul, Sanguannam, Sangwongngam et al. (2015); You, Liu and Wang (2012)], the behavior of nodes was studied through the success probability of communication between nodes, the possible existence of a variety of unsafe behavior in the network was not considered. In fact, similar with the condition in classical network, the node behavior in quantum communication network can be expected, managed and evaluated.

The problem of multi-user quantum secure communication and secret information sharing
There have been many results about multi-user quantum secure communication and secret information sharing. In the study of multi-user quantum secure communication, Fröhlich et al. [Fröhlich, Dynes, Lucamarini et al. (2013)] proposed a quantum access network (a network node can share the key exchange with 64 users). Chang et al. [Chang, Jin, Jong et al. (2012)] proposed a multi-user quantum network system based on X-type entangled state. Salvail et al. [Salvail, Momtchil, Eleni et al. (2010)] studied a trusted relay QKD network (to ensure the authenticity and privacy of a key). Sun et al. [Sun, Cheng and Ji (2014)] studied a trusted relay QKD network with differentiated services. David et al. [David, Jesus, Alex et al. (2013)] proposed a secure optical network based on QKD and weakly trusted relay. Lin et al. [Lin, Huang and Liu (2013)] put forward a multi-user QKD scheme based on mutual authentication and Bell state. William et al. [William, Razieh, Ma et al. (2015)] introduced a QKD scheme based on trusted relay node. About the study of multi-user secret information sharing, Zhang et al. [Zhang, Liu and Li (2011)] proposed a quantum secret sharing (QSS) scheme based on error correcting code. Sun et al. [Sun, Xu, Chen et al. (2013)] presented a scalable QSS network. Bell et al. [Bell, Markham, Wadsworth et al. (2014)] demonstrated the experiment of QSS based on graph state. Li et al. [Li, Long, Chan et al. (2011)] presented a secret sharing scheme without a trusted party. Wang et al. [Wang, Zou and Zhao (2014)] proposed a QSS scheme with secure and trusted center. Li et al. [Li, Zubairy and Al-Amri (2018)] proposed a scheme of quantum Secure Group Communication. However, these studies mentioned above are mainly from the perspective of expanding the number of users. In fact, similar with classical network, to fulfill quantum communication network and practical, ensuring network security and normal operation is one of the most important tasks, except to expand the node (user) scale. To ensure the normal operation and security of multi-user quantum network, the identity and behavior of nodes waiting for accessing the network should be authenticated and controlled effectively. In summary, the research results mentioned above laid the foundation for the research of secure and reliable quantum communication network. But these achievements promoted the practical and networking of quantum communication, either establishing trust between two sides of communication through quantum identity authentication or quantum bit commitment, either evaluating the trust of node with the success probability of quantum communication, or achieving multi-user quantum communication and secret information sharing by expanding the amount of users. Multiple factors and the fuzzy features of these factors are not considered, which affect the trust of nodes, such as the historical reputation degree of nodes, the probability of successful communication, the identity information of nodes and the location of nodes. In multi-user quantum communication network, how to evaluate the trust of nodes securely, how to manage node behavior trustedly and how to access node in network trustedly are not considered. Therefore, it is of great significance for the research of trust management and trust management model in quantum communication network, which is bound to promote the practical and networking of quantum communication, and it will be a research hotspot in establishing secure and reliable quantum communication network.

Conclusions
Quantum communication is a new cross discipline combining classical information theory and quantum mechanics, which using quantum state to carry information. Quantum communication is expected to break through the limit of classical communication technology in the aspects of communication security, computing power, information transmission, channel capacity and measurement accuracy, which has become a new direction and will be the mainstream in the field of communication and information in twenty-first century. This paper summarized the research status of theory and technology in quantum communication and quantum communication network. The key technologies of establishing secure and reliable quantum communication networks are classified and summarized. The problems and trend of each direction in trust management of quantum communication network are discussed in depth. Therefore, it is of great significance to further develop the theory and application study of secure and reliable quantum communication networks.