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Blockchain is a distributed database based on the Bitcoin platform.It has attracted widespread attention from academia and industry because of its characteristics of decentralization,traceability,and non-tamperability.However,with the rapid growth of the number of nodes and the amount of data,problems such as low throughput and difficult storage scalability appear.The problem of storage scalability of blockchain has become a bottleneck for blockchain applications.Therefore,this paper focuses on the summary and prospect of storage scalability of blockchain.Firstly,this paper introduces the basic knowledge and data structure of blockchain and analyzes the problems of storage scalability of blockchain at present.Secondly,this paper explains the principles,implementation methods,research progress,advantages,and disadvantages of the 0th layer expansion scheme,the on-chain expansion scheme,and the off-chain expansion scheme.Finally,this paper analyzes the challenges in the current blockchain sto-ragescalability scheme and provides a direction for the next blockchain research work.

Aiming at the problem that the classical blockchain consensus mechanism is under the threat of quantum computing attacks,a quantum-secured Byzantine fault tolerant consensus mechanism is proposed.Firstly,to solve the security threat of public key digital signature,this paper proposes a multilinear hash-unconditionally secure signature(MH-USS) signature scheme based on quantum key distribution (QKD) and multilinear hash function family.In this scheme,quantum keys are distributed through QKD network,messages and signatures are transmitted through classical network,and the simplified USS signature scheme is adopted as the main framework,combined with the family of multiple linear hash functions,to generate a new USS scheme.This signature scheme has the characteristics of unforgeability,non-repudiation and transferability.Moreover,this scheme can be implemented on existing equipment and has high practical value.Secondly,in view of the relatively low consensus efficiency of the classical Byzantine fault-tolerant consensus mechanism PBFT,this paper proposes the quantum secured-byzantine fault tolerance(QS-BFT) consensus mechanism.By adding “fast-normal” consensus mode and allowing nodes to vote on empty blocks,the system communication times are reduced and the view conversion process is avoided.It has been proved that this scheme not only guarantees the safety and liveness,but also effectively reduces message complexity and improves consensus efficiency.The simulation and performance test for this scheme indicate that the throughput of this scheme is higher and the delay is lower compared with the PBFT consensus mechanism which is based on the MH-USS signature scheme.

Based on blockchain technology,Ethereum Solidity smart contract as a computer protocol is designed to spread,verify,or execute contracts in an informative way,and it provides a foundation for various distributed application services.Although implemented for less than six years,its security problems have frequently broken out and caused substantial financial losses,which attracts more attention in the security inspection research.This paper firstly introduces some specific mechanisms and operating principles of smart contracts based on Ethereum related techniques,and analyzes some smart contract vulnerabilities occurring frequently and deriving from the characteristics of smart contracts.Then,this paper explains the traditional mainstream smart contract vulnerability detecting tools in terms of symbolic execution,fuzzing,formal verification,and taint analysis.In addition,in order to cope with the endless new vulnerabilities and the need to improve the efficiency of detection,vulnerabilities detection based on machine learning in recent years is classified and summarized according to the various ways of problem transformation in three perspectives including text processing,non-Euclidean graph and standard image.Finally,this paper proposes to formulate more extensive and accurate standardized information database and measurement indicators towards the insufficiency of the detection methods in two directions.

Voting is a commonly used method in modern democratic society,involving many fields such as politics,stock companies,court decisions,etc.Voting is regarded as a specific form of balloting,with only two candidates in pro and con.Blockchain is a digital accounting technology with the characteristics of time stamp,openness and non-tamperability which satisfy the transpa-rency and verifiability of voting.In order to realize the anonymity of voting,this paper uses ring signature to hide the correspondence between voting content and the voter.This paper puts forward a hierarchical anonymous voting scheme,which realizes the legitimacy,confidentiality,non-repeatability,updateability and verifiability of voting.By creating a hierarchy mechanism for the voting of virtual identities,it can be used in situations where the votes vary from vote to each voter,and this agreement applies the threshold ring signature scheme to the voting scene for the first time,making the voting process simple and efficient for the final voting results once one party has more than half of the votes cast.

Smart contract is an important component of blockchain platform to realize transactions,which provides an effective solution to the trust problem between multi-party transactions.Smart contracts not only manage high value tokens but also have the characteristics of immutable,which lead to the security threats of smart contracts many times in recent years.At present,a lot of researches have devoted to the security of smart contracts,among which the vulnerability detection of smart contracts has become the main concern.This paper analyzes the security of smart contract systematically.From the perspective of whether to execute the smart contract,vulnerability detection tools are divided into static detection tools and dynamic detection tools.In particular,the vulnerability detection ability of existing detection tools is analyzed,and the principles,advantages and disadvantages of 16 detection technologies are discussed.Finally,the paper gives a prospect of how to improve the security of intelligent contract,and puts forward three research directions which may improve the security of smart contract.

Blockchain as a Service is a new application method that embeds the blockchain framework into the cloud computingplatform,which can effectively use the cloud platform to improve the convenience and efficiency of the deployment and operation of the blockchain system.This paper mainly analyzes and summarizes the key techniques and existing platform systems of Blockchain as a Service.Firstly,this paper introduces the concept and function of BaaS platform,and analyzes the advantages of BaaS platform in improving safety performance,realizing personalized customization and reducing development cost.Then,based on the existing commercial BaaS platform,the system architecture and key technique architecture of BaaS platform are introduced in detail,and the characteristics,technologies and functions of the current mainstream BaaS platform,as well as the relevant application scenarios are introduced.In this paper,the challenges encountered by the current BaaS platform are summarized,and the future research direction of BaaS is prospected.

Focusing on the problems of poor scalability,the random selection of primary nodes,and high network overhead in the practical-Byzantine-fault-tolerant consensus algorithm,this paper proposes a Byzantine-fault-tolerant consensus algorithm based on credit evaluation mechanism.First of all,the system sets different roles for the nodes in the cluster and assigns different permissions to the nodes according to different roles,so that the nodes with different permissions can enter and exit the network dynamically.Secondly,the voting mechanism and follow-the-satoshi algorithm based on credibility are designed to ensure the security and fairness of the election.Finally,in the aspect of the consensus process,an optimized two-stage Byzantine-fault-tolerant consensus is proposed to reduce the network overhead in the PBFT consensus process.Experiments show that the consensus algorithm based on the credit evaluation mechanism proposed in this paper has the characteristics of high dynamic,election security,and low cost compared with the PBFT algorithm which is suitable for the alliance chain.

This paper proposes a mobile edge computing (MEC) assisted blockchain system in which mobile terminals (MT) do not have enough local computation resources to solve the proof of work (PoW) puzzle.By combining the computation resource allocation of MTs and edge server (ES) with the revenue sharing of MTs,a joint optimization problem is formulated to maximize the system-wide utility of all MTs and the ES.To solve the optimization problem efficiently,a multi-layer decomposition algorithm based on cyclic block coordinate descent (CBCD) is proposed.First,given the revenue sharing variables in advance,the corresponding sub-problem can be solved to obtain the computation resource allocation results of both MTs and ES.Then,with the obtained computation resource allocation,the revenue sharing variables of MTs are optimized.Finally,this paper optimizes the two sub-problems alternately until the algorithm reaches convergence.The numerical results show that the proposed algorithm can obtain the optimal solution of the joint optimization problem effectively and improve the system-wide utility.

With the development of blockchain technology,smart contracts have been widely used in various fields,and Ethereum has become the largest smart contract platform.At the same time,the frequent smart contract vulnerabilities have caused huge economic losses.The vulnerability detection of smart contract has become the focus of research,while the previous smart contract vulnerability detection tools can not make good use of the syntax information of the contract source code.Aiming at the re-entrancy vulnerability of smart contract,firstly,this paper proposes SCDefender,a vulnerability detection tool based on deep learning.Taking the abstract syntax tree form of the Solidity source code of smart contract as the research object,the tree-based convolutional neural networks is used for vulnerability detection.Secondly,an abstract syntax tree pruning algorithm is proposed to remove the nodes irrelevant to the vulnerability detection task and retain the key information in the abstract syntax tree.The accuracy,recall rate and F1 value of SCDefender vulnerability detection is 81.43%,92.12% and 86.45% respectively,which has a good vulnerability detection effect.Ablation experiments show that the abstract syntax tree pruning algorithm has an important contribution to the vulnerability detection task of SCDefender.

In traditional service-oriented architecture(SOA),web service providers register their service descriptions in the registry for service consumers to discover and invoke services.Traditional SOA lacks dispute resolution mechanism,so that the trusted service invocation between service consumers and providers can not be guaranteed.Blockchain can be reasonably introduced into the dispute resolution mechanism due to its significant advantages in decentralization and tamper resistance.Therefore,this paper proposes a trusted SOA architecture based on blockchain,in which blockchain acts as evidence recorder and service registry agent. During a service trusted invocation,the service consumer first encrypts the parameters and sends them to the target service provider.Secondly,the service provider receives the encryption parameters and decrypts them.Then,the service provider completes the service execution and encrypts the output result.Finally,when the service provider sends the encryption result to the service consumer,it completes the trusted credential construction and uplink.Based on the above,when a service dispute occurs,it will trigger the adjudication of the smart contract.The execution of the contract relies on trusted vouchers to correctly handle service disputes.Experimental results show that,compared with the traditional invocation,the proposed method can correctly handle the service disputes between service providers and requesters on the premise of ensuring that the growth rate of trusted invocation time of most services is no more than 30%.

Sharding is a technology that solves the problem of blockchain capacity expansion.However,sharding may make it ea-sier for malicious nodes to be concentrated in a single shard,thus hindering the safe operation of the entire system.This paper proposes a reputation-based sharding consensus protocol(RBSCP),which establishes a reputation mechanism to measure node behavior and encourage nodes to follow the protocol.The reputation level-based sharding method reduces the difference in the reputation level distribution in different shards,so as to prevent malicious nodes from concentrating on a single shard to do evil.A double-chain model combining verification chain and record chain is proposed.Through the differentiated storage of transactions,the storage capacity of the blockchain is expanded while the security of the blockchain is improved.By associating the vo-ting shares with the node reputation and differentiating the node commitments,a reputation-based fast Byzantine fault tolerance(RFBFT) algorithm is proposed,which enables honest nodes to reach consensus faster and reduces the impact of malicious nodes.Security analysis shows that RBSCP can guarantee the rationality of node distribution in shards and the security of consensus process,and prevent double spend attack and nothing at stake attack.Experimental results show that RBSCP can achieve low sharding latency,low consensus latency and high throughput under the premise of ensuring security.

The decentralization of blockchain can easily lead to the leakage of users’ private data at the transaction layer,which in turn leads to information security issues.The zero-knowledge range proof is designed to confidentially verify that the transaction data belongs to a legal positive integer range without revealing the transaction data.It effectively solves the problem of blockchain privacy leakage.The existing blockchain range proof scheme can still be further optimized in terms of proof speed,verification speed and calculation cost.In addition,the existing solutions cannot handle the floating-point number problem,thus limiting the application fields of range proofs.This paper proposes an efficient range proof scheme with constant computational cost and universal for floating-point numbers and integers,ZKFERP.It improves the zero-knowledge protocol based on Bulletproofs to optimize the proof structure,and a Lagrangian inner product vector generation method is designed to make the witness generation time constant and the commitment is constructed according to the floating-point number range relationship to implement floating-point range proof.ZKFERP only relies on the discrete logarithm assumption,and third-party credibility is not required.The communication cost and time complexity of ZKFERP are constant.Experimental results show that,compared with the most advanced known range proof scheme,ZKFERP’s proof speed is increased by 40.0%,and the verification speed is increased by 29.8%.

With the continuous development and innovation of blockchain technology,a large number of blockchain-based applications have been generated.Today’s blockchain systems are mostly heterogeneous and not interconnected,and there is no direct value circulation between chains.This greatly limits the functional expansion and development of blockchains.Cross-chain technology refers to the exchange of information between different blockchain system instances and the use of the exchanged information to achieve interconnection and value transfer between blockchains.Firstly,this paper introduces the development process of blockchain cross-chain technology,and introduces in detail four current mainstream cross-chain technologies including the notary mechanism,the side chain relay,the hash lock and the distributed private key control.Then,based on the above-mentioned cross-chain technology,it further introduces several current mainstream cross-chain projects and applications.Finally,by comparing the similarities and differences of several cross-chain technologies in trust model,security,atomicity,scalability,etc.,the current development trend of cross-chain technology is summarized and analyzed,and the difficulties and future development direction in the field of cross-chain are discussed.

Crowdsourced testing is the application of crowdsourcing in software testing.It performs testing in a distributed and collaborative way,which has received widespread attention.However,the open crowdsourced testing environment and centralized storage mode put the intellectual property at risk of leakage and being manipulated.In order to realize the privacy protection and trusted storage of crowdsourced testing intellectual property,this paper proposes corresponding protection methods for different intellectual property.For the test tasks and the tested codes,AES and the improved CP-ABE algorithm are used for fine-grained data access control.By outsourcing complex encryption operations to the trusted third party,the proposed algorithm reduces the computing cost of requester.Meanwhile,it also supports the dynamic attribute revocation and meets the forward and backward security.In addition,using blockchain and InterPlanetary File System (IPFS),a distributed trusted storage and consistency right confirmation method of large-scale intellectual property data is realized.It protects intellectual property data from tampering and helps to solve intellectual property disputes.Finally,the performance test and comparative evaluation verify that the encryption and decryption efficiency of this method is improved compared with previous methods,and the blockchain has a high perfor-mance.Security analysis shows that the scheme meets the security requirements.

Since the advent of Bitcoin in 2008, blockchain has gradually become a research hotspot in academia.As the key technology of blockchain, consensus algorithm has also attracted more attention from researchers.It's easy to introduce Byzantine fault nodes in blockchain system because of its complex and variable runtime, so the blockchain Byzantine fault tolerant consensus algorithm is a difficulty that must be overcome.This paper systematically summarizes the research progress of the blockchain Byzantine fault tolerant consensus algorithm, in order to provide a reference for the innovation of consensus algorithms in the future.Firstly, sorting out the four major factions of the existing blockchain Byzantine fault tolerant consensus algorithms and introducing the BFT consensus algorithm.Secondly, reviewing several important values in the classic PBFT algorithm and its correctness proof.Thirdly, putting forward the four optimization goals of the BFT consensus algorithm:decentralization, efficiency, fault tolerance rate and security.Then, based on the dimensions of consensus rounds, number of consensus nodes, underlying hardware, communication mode or encryption algorithm, probability of fault nodes, five optimization ideas of BFT consensus algorithm are summarized.Finally, analysising 10 classic BFT consensus algorithms in detail and making performance comparison.

Federated learning has solved the problem of data interoperability under the premise of satisfying user privacy protection and data security.However,traditional federated learning lacks an incentive mechanism to encourage and attract data owners to participate in federated learning.Meanwhile,the lack of a federated learning audit mechanism provides the possibility for malicious nodes to conduct sabotage attacks.In response to this problem,this paper proposes a reliable federated learning incentive mechanism for electric metering data based on blockchain technology.This method starts from two aspects:rewarding data parti-cipants for training participation and evaluating data reliability for all of them.We design an algorithm to evaluate the training effect of data participants.The contribution of data participants is determined from the perspective of training effect and training cost,and the participants are rewarded according to the contribution.At the same time,a reputation model is established for the reliability of the data participants,and the reputation of the data participants is updated according to the training effect,so as to achieve the reliability assessment for data participants.Based on the open-source framework of federated learning and real electric metering data,a case study is carried out,and the obtained results verify the effectiveness of our method.

Plain text information hiding is vulnerable to active attacks such as deletion and change,which makes the embedded secret information damaged.Blockchain is characterized by non-tampering,non-forgery,anonymity and node information synchronization,making it a natural platform for building hidden channels and ensuring that secret information is not destroyed.This paper proposes the blockchain covert communication model for plain text information hiding.Firstly,the location of the embedded secret information is determined according to the partial order relation.The sender uses the space method to embed the secret information into the plain text content.Then,a scenario of hidden communication in the blockchain network is constructed,and the sender publishes the transaction containing the plain text content to the blockchain network.Finally,after the transaction is packaged and a chain block is formed,any node can obtain the file as the receiver,but only the trusted party can extract the secret information through the inverse process of the embedded algorithm.Experimental comparison and analysis show that the model has better anti-detection,robustness,security and higher hiding capacity.More importantly,the blockchain as a channel enables the identity of the trusted party to be hidden,and the concealment of the communication process is doubly guaranteed.

Faced with a large number of IoT transactions,efficient consensus algorithm plays a key role in the application of blockchain technology into IoT.In this paper,according to the problems of long consensus time delay and low throughput in practical Byzantine fault tolerant algorithm (PBFT),we propose a practical Byzantine fault tolerant algorithm based on clustering (C-PBFT).Firstly,the nodes are clustered according to location features to form a network structure with multiple centers and layers.Then,consensus tasks are divided to conduct consensus in bottom and top network,thereby reducing the communication cost needed by consensus.Finally,credibility of dynamic credit model evaluation node is introduced to reduce the participation of abnormal nodes and increase the security and reliability of the system.Experimental results show that the C-PBFT algorithm can effectively reduce communication overhead,consensus delay and improve throughput.

Blockchain technology can be extensively applied in diverse services,ranging from online micro-payment,supply chain tracking,digital forensics,health-care record sharing to insurance payment.Extending the technology to the crowdsourcing,we can obtain a verifiable and traceable crowdsourcing systems.Emerging research in crowdsourcing applications exploits blockchain technology to optimize the task assignment and reward payment using various consensus protocols and blockchain techniques,which can provide additional security,automatic,verifiable and traceable crowdsourcing platforms.In this paper,we conduct a systematic survey of the key components of crowdsourcing blockchain and compare a number of popular blockchain applications.In particular,we first give an architecture overview of popular crowdsourcing-blockchain systems by analyzing their network structures and protocols.Then,we discuss variant consensus protocols for crowdsourcing blockchains,and make comparisons among different consensus algorithms.Finally,we look forward to the future research problems in this field,and provide a large number of references.

Mixing is an important way for privacy protection among digital currency such as Bitcoin.However,on the one hand,Bitcoin mixing protects user privacy,on the other hand,it facilitates the transfer of assets for illegal activities such as ransomware and Bitcoin theft.In this paper,we propose a traceable scheme for Bitcoin mixing.The scheme aims to protect the privacy of legi-timate users and can trace the illegal assets.The system is regulated by trusted third party,user anonymity and traceability based on the group signature which is constructed by bilinear groups and strong Diffie-Hellman assumption.When there is a need for tracing,the regulator can determine the signed user through the system private key,so as to determine the illegal asset transfer path.Security analysis shows that the scheme can trace the illegal asset transfer without modifying the current Bitcoin system,meanwhile,the solution provide privacy protection and asset safety for legitimate users.Furthermore,the scheme provides a refe-rence direction for the research on digital currency privacy protection.

Bitcoin is one of the most mature public chain application systems,the user key is the critical factor to the process of determining the ownership of Bitcoin,the security of Bitcoin is guaranteed by the safe management of the user key,and the loss of the key will lead to the loss of a large number of user assets.So it is an urgent problem to recover the lost assets.This paper proposes a key update mechanism in Bitcoin based on the improved P2PKHCA (pay-to-public-key-hash-with-conditional-anonymity) script scheme to solve above problems.Firstly,the key generation algorithm in the P2PKHCA scheme is improved by introducing the key life cycle and random number to solve its key leakage problem.Secondly,the two new opcodes,OP_KEYUPDATE and OP_TSELECTION,are proposed to design the new key update script to realize the user key update of the Bitcoin system.Finally,two types of key update schemes based on the key update script are constructed to make the script suitable for the requirements of different key update applications.The security analysis and performance analysis of the key update mechanism show that the proposed mechanism realizes the recovery of lost Bitcoins in the Bitcoin system on the premise of the effective completion of update of user's key.

Although the application of big data in legislative evaluation helps to get rid of chronic diseases such as single evaluation subject,data omission,data distortion and formalization of conclusions.However,there are still some defects,such as lack of public participation under the dominant mode of the legislature,improper cleaning methods leading to poor data quality,information asymmetry,trust crisis caused by "algorithm black box",and biased evaluation conclusions caused by algorithm bias.Based on the approach of technology-system collaborative evolution theory,this paper applies the blockchain which is consistent with the nature of big data to innovate the underlying architecture,makes up for the defects in the application of big data in legislative evaluation,and then constructs an anastomosing application model of "big data＋block chain",optimizes the legislative evaluation system with public participation incentive mechanism,data cleaning and review mechanism,consensus formation negotiation platform and procedure justification circulation platform,so as to fully release the system function of legislative evaluation to gather public opinion and wisdom,strengthen democratic supervision and improve the quality of legislation.

The concept of "network perimeter" in industrial control system is becoming vague due to the integration of IT and OT technology.The fine-grained access control strategy that intends to protect each network connection can ensure the network security of industrial control system.The role-delegation-based access control scheme can delegate an access right of user in a domain to a user in another domain or a company partner so that these users can remotely access the network resources of the industrial enterprise.However,these benefits resulted from the delegation may increase the attack surface for industrial control system.The blockchain technology with decentralization,tamper-proof,auditable and other characteristics can be considered as a basic framework of the role-delegation access control for network resources in industrial control system.This paper proposes a role-delegation access control scheme DRBAC based on blockchain.DRBAC includes several important components:user role management and delegation,access control,monitoring mechanism,etc.The DRBAC solution is implemented based on smart contract.The DRBAC ensures that each network connection must be protected by fine-grained access control strategies.Finally,the correctness,feasibility and overhead of DRBAC are tested and analyzed in a private blockchain network.

As a consortium blockchain with the multi-center characteristics of public blockchain and the high-performance advantages of private blockchain,it has become the center of development of China.Combined with the characteristics of node trust in the consortium blockchain,non-byzantine fault tolerance consensus algorithm can provide better performance support for the consortium blockchain.By selecting Raft consensus algorithm as the research object,focusing on the leader election and log replication process in the Raft consensus algorithm,this paper proposes a non-byzantine fault tolerance consensus algorithm for consortium blockchain Kraft(Kademlia-Raft) consensus algorithm.It improves the process of Leader election and log replication in the Raft consensus algorithm by combining the two-layer Kademlia routing protocol.First,in view of the problem of voting efficiency caused by the number of Candidate nodes and the increase of Follower nodes in the Raft consensus algorithm,KRaft consensus algorithm uses K-bucket established by the two-layer Kademlia protocol to realize the stable election in the Candidate node set.Se-condly,in view of the low efficiency of the single-node log replication process of the Leader in the log replication process of Raft consensus algorithm and the load balance problem on the nodes,a parallel log replication scheme of multiple Candidate nodes is proposed to equalize the load on the Leader node,so as to improve the data throughput and the scalability of the algorithm at the same time.Finally,the local multi-node simulation experiment shows that the data throughput of KRaft consensus algorithm is increased by 34.5% compared with Raft consensus algorithm,the voting speed of Leader node is increased by 55.6%.