PoEC:A Cross-Blockchain Consensus Mechanism for Governing Blockchain by Blockchain

Jieren Cheng,Yuan Zhang,Yuming Yuan,Hui Li,Xiangyan Tang,Victor S.Sheng and Guangjing Hu

1School of Computer Science and Technology,Hainan University,Haikou,570228,China

2School of Cyberspace Security,Hainan University,Haikou,570228,China

3Hainan Blockchain Technology Engineering Research Center,Haikou,570228,China

4Hainan Huochain Tech Company Limited,Haikou,570100,China

5Department of Computer Science,Texas Tech University,Lubbock,79409,United States of America

Abstract:The research on the governing blockchain by blockchain supervision system is an important development trend of blockchain technology.In this system there is a supervisory blockchain managing and governing the supervised blockchain based on blockchain technology,results in a uniquely cross-blockchain demand to consensus mechanism for solving the trust problem between supervisory blockchain and supervised blockchain.To solve this problem,this paper proposes a cross-blockchain consensus mechanism based on smart contract and a set of smart contracts endorse the crossblockchain consensus.New consensus mechanism called Proof-of-Endorse-Contracts(PoEC)consensus,which firstly transfers the consensus reached in supervisory blockchain to supervised blockchain by supervisory nodes,then packages the supervisory block in supervisory blockchain and transmits it to the smart contract deployed in the supervised blockchain,finally miners in supervised blockchain will execute and package the new block according to the status of the smart contract.The core part of the consensus mechanism is Endorse Contracts which designed and implemented by us and verified the effectiveness through experiments.PoEC consensus mechanism and Endorse Contracts support the supervised blockchain to join the governing blockchain by blockchain system without changing the original consensus mechanism,which has the advantages of low cost,high scalability and being able to crossblockchain.This paper proves that our method can provide a feasible crossblockchain governance scheme for the field of blockchain governance.

Keywords:Proof-of-endorse-contracts;PoEC;cross-blockchain consensus mechanism;governing blockchain by blockchain

1 Introduction

1.1 Background

Blockchain is a technology that is maintained by multiple parties jointly and uses cryptography to ensure the security of transmission and access,which can achieve data consistency,immutability and non-repudiation[1],realizing the transformation from information Internet to value Internet[2].Blockchain is becoming another emerging technology that has a significant impact after big data,cloud computing,artificial intelligence,virtual reality,etc.[3].Its application has extended from the initial digital currency to finance,Internet of Things,intelligent manufacturing and other fields,attracted extensive attention from the industry and governments of various countries[4].

Blockchain supervision technology is the key to ensure the healthy and sustainable development of blockchain technology and industry[5].However,the anonymity of blockchain network,the immutability of blockchain transactions and the distributed authority of blockchain nodes make it difficult to govern the abnormal and illegal behaviors of blockchain[6].For example,the governance measures taken after The DAO project suffered a reentrant attack directly led to the hard forks of Ethereum[7].This shows that the traditional governance method oriented a centralized architecture cannot govern the public blockchain well,and a powerful governance method that can transform the consensus of the governing body into the governing object is urgently needed,that is,the consensus of the public blockchain network.It is simply imagined that this process must require the deep involvement of blockchain technology.Therefore,Academician Chen Chun of The Chinese Academy of Engineering pointed out that the research on the supervision system of governing blockchain by blockchain is an important development trend of blockchain supervision technology at The Blockchain Technology Conference 2019CCF[8].

1.2 Motivations,Problems and Challenges

The governing blockchain by blockchain regulatory system refers to transforming the blockchain governance scheme into the code-based rule paradigm in the blockchain network with the help of consensus mechanism,smart contract,incentive mechanism and other key blockchain technologies[9],to coordinate the legitimate interest demands of non-specific subjects.It supports supervisory nodes included in supervised blockchain to form supervisory blockchain,to review and govern smart contracts and node transactions in accordance with established rules,and to cancel and impose fines on non-compliant contracts or transactions[10],thus effectively reviewing,monitoring and governing the blockchain community,which is shown in Fig.1.

In general,the supervisory blockchain is a permissioned consortium chain or private chain composed of regulatory nodes,with access mechanism and long-term fixed access.The network model is synchronous network or partially synchronous network.The supervised blockchain is usually a permissionless public chain,and in a few cases,it is a permissioned consortium chain.Nodes typically have no access mechanism and free to join or leave.The network model is asynchronous network or partially synchronous network[11].Tab.1 summarizes the main differences between the supervisory and supervised chains in eight aspects.

The heterogeneous characteristics of the supervising blockchain and the supervised blockchain in terms of access,node connection,network model and other aspects bring great challenges to the traditional consensus mechanism designed for homogeneous blockchain.In particular,the hierarchical cross-blockchain regulatory model puts forward a unique demand for cross-blockchain consensus mechanism,which makes the existing consensus mechanism unable to be directly applied to the governing blockchain by blockchain framework.Therefore,it is urgent to study the scalable crossblockchain consensus mechanism oriented to the governing blockchain by blockchain framework to solve the applicability problem of the closed single-chain consensus mechanism.

1.3 The Contributions

This paper proposes a new cross-blockchain consensus mechanism based on intelligent contract to meet the requirements of both supervision and governance in chain-governing application scenarios.The new consensus mechanism is known as the Proof-of-Endorse-Contract(PoEC),which supports the supervisory blockchain to transfer the consensus reached to the smart contract in the supervised blockchain,and then the miners in the supervised blockchain will package and verify the new block according to the status of the smart contract.PoEC protocol supports the supervised blockchain to join governing blockchain by blockchain system without changing the original consensus mechanism,which belongs to a kind of cross-blockchain consensus mechanism with scalability.

1.4 The Structure of Paper

The rest of this article is structured as follows.In Section 2 we briefly introduce the work related to consensus mechanism.Section 3 outlines the design and architecture of Proof-of-Endorse-Contract(PoEC)consensus mechanism.Next in Section 4 we introduce the implementation details of Endorse Smart Contacts.Section 5 presents the designs and settings of experiments,as well as discussion of the experiment results.Finally,we summarize our contributions and discuss future research directions in Section 6.

2 Related Work

Since our paper mainly discusses the subject of consensus agreement,we have made a brief literature review of the mainstream consensus mechanism,analyzed the main ideas and characteristics,and discussed its applicability in the multi-stage,heterogeneous,cross-blockchain governing blockchain by blockchain application scenario,to lay a foundation for the discussion of our PoEC consensus protocol in Chapter 3.Consensus mechanism can usually be divided into classical distributed consensus mechanism and blockchain consensus mechanism,among which the classical distributed consensus mechanism is also known as Byzantine consensus mechanism[12],and blockchain consensus mechanism can usually be divided into Proof-of-X(PoX)consensus mechanism,authorization consensus mechanism and mixed consensus mechanism.

2.1 Classic Distributed Consensus Mechanisms

The classical distributed consensus mechanism is the consensus mechanism used in the traditional distributed network,which realizes the distributed consensus through the state machine replication between network nodes.In[13]proposed the Byzantine General problem and studied how non-fault nodes reach agreement on specific data in the case of possible failure nodes or malicious attacks,which became the basis for the research on consensus mechanism.In[14]proposed a Paxos algorithm to solve the Problem of Byzantine generals.This algorithm can tolerate the collapse of a certain number of nodes in the network,to reach an agreement on a specific value in the distributed system.In[15]proposed the Practical Byzantine Fault Tolerance (PBFT).As a solution to the Byzantine generals’problem,PBFT could achieve the final consensus among honest nodes while the number of enemies was no more than 1/3 of the total number of nodes.In[16]proposed a new common algorithm:Mixed Byzantine Fault Tolerance (MBFT).Functionally,MBFT partitions the nodes participating in the consensus process and improves scalability and efficiency without sacrificing security.MBFT also introduces a random node selection mechanism and a credit mechanism to improve security and fault tolerance.In[17]proposed a dynamic reputation practical Byzantine fault tolerance algorithm.The dynamic reputation practical Byzantine fault tolerant algorithm adopts the consensus election method based on credit.The monitoring node divides the remaining nodes into two types of nodes according to their reputation values:consensus nodes and auxiliary nodes,which participate in different stages of the block generation process respectively,and dynamically update the consensus nodes with low reputation scores.

2.2 PoX Consensus Mechanism

PoX consensus mechanism is usually a blockchain consensus mechanism oriented towards public chain.Its core idea is to determine the probability and expectation of the nodes to obtain the accounting right based on the proportion of certain key resources owned by the nodes,to improve the security of the public chain network.In[18]realized the design of bitcoin system based on the traditional Proof-of-Work(PoW),and the blockchain was proposed for the first time as its underlying technology.In[19]proposed Proof-of-Stake,and introduced the concept of age of currency for the first time.The core idea is that the more coins a node has and the longer it has been holding coins,the more likely it will be chosen as a blocker.In[20]proposed Permacoin based on Proof-of-Capacity(PoC),which requires participants to be able to store part of a large file.In[21]proposed a novel lightweight Proof-of-Block&Trade(PoBT)algorithm for the blockchain of the Internet of Things and its integrated framework,which can verify transactions and blocks with reduced computing time.In[22]proposed a novel consensus mechanism called Proof-of-Negotiation (PoN).PoN introduced a trust mechanism to realize the random selection of honest miners and conducted a round of block creation through a negotiation mechanism.

2.3 Authorization Consensus Mechanism

The main idea of authorization consensus mechanism is to complete the generation and maintenance of blocks through distributed consistency algorithm after nodes have been authenticated.In[23]proposed the basic framework for Hyperledger Fabric.Hyperledger Is a series of open source blockchain projects initiated by the Linux Foundation,which aims to provide an enterprise-class open source distributed ledger framework and source code.Hyperledger Fabric is a communitybased project that provides a supporting framework for blockchain applications.In[24]proposed the DFINITY consensus mechanism.DFINITY protocol operates in periods and divides all participating nodes into different groups.A random committee is responsible for transaction processing and consensus operation in each period,and at the end of each period,a random number function is used to determine the group serving as the committee in the next period.The PaLa consensus mechanism proposed by[25]realizes the rapid consensus in the authorization network.PaLa uses the method of parallel pipeline to improve the efficiency of block processing and adopts the subcommittee sliding window reconfiguration to ensure the sustainability of transaction processing during the reconfiguration.

2.4 Hybrid Consensus Mechanism

The main idea of hybrid consensus mechanism is to select some nodes as the consensus committee through PoX consensus mechanism and run Byzantine consensus mechanism inside the Committee to complete the generation of blocks.In[26]first combined the classical distributed consistency algorithm PBFT with blockchain and proposed the PeerCensus consensus algorithm.Bitcoin is used as the underlying chain to select a certain number of nodes and complete the generation of the final block through the Chain Agreement (CA) algorithm after their identity authentication.In[27]proposed the Hybrid Consensus mechanism,which realized state machine replication in an unauthorized environment by using workload proof.Hybrid Consensus for the first time uses formal security model and modular design to model the Hybrid consensus mechanism,and proves that it can meet the safety characteristics such as consistency and activity.In[28]proposed ELASTICO,a fragmentation consensus mechanism,which divides nodes participating in consensus into multiple groups,outputs a block from each group and then obtains the total block.In[29]proposed the RapidChain consensus mechanism,which realized computing sharding,communication sharding and storage sharding.Its main modules include startup,consensus and reconfiguration.In[30]proposed a Proof-of-QoS(PoQ)based on Quality-of-Service (QoS).In this validation protocol,the whole network is divided into several small regions,each region specifies a node according to its QoS,and then runs deterministic Byzantine fault tolerant consensus among all the specified nodes.

Although the above-mentioned consensus mechanisms on the indices such as security and efficiency have excellent performance,but the consensus mechanism is still facing single-chain or homogeneous blockchain,cannot be directly applied to multilevel heterogeneous and cross-blockchain application scenario of governing blockchain by blockchain.It still needs a kind of safe,efficient and scalable cross-blockchain mechanism for governing blockchain by blockchain framework.

3 The Proof-of-Endorse-Contract Consensus Mechanism

The Proof-of-Endorse-Contract (PoEC) consensus mechanism is a cross-blockchain consensus mechanism designed for the scenario of chain regulation.

3.1 Design Requirements for PoEC

There are two main functional requirements in the governing blockchain by blockchain model:supporting the chain of supervision to obtain the data of the supervised blockchain;Support the supervised blockchain to implement the reward and punishment measures given by the supervised blockchain.Among them,the reward and punishment measures are mainly divided into incentive measures and punishment measures.Incentive measures are mainly public chain nodes that participate in the consensus mechanism.How to set the incentive measures is determined by the incentive mechanism,and the implementation of incentive measures is relatively simple.After the supervised blockchain reaches consensus on the incentive measures,at least m of the N supervision nodes can initiate the transfer transaction based on the multi-signature algorithm.Penalties can be specified in three ways:fines,trade bans and frozen balances(while rollbacks are too limited to be considered).From the perspective of consensus mechanism,the essence of realizing penalty is to force the supervised blockchain to accept certain transactions,while the essence of realizing prohibited transaction and frozen balance is to force the supervised blockchain not to accept certain transactions.At the same time,the consensus mechanism has the non-functional requirements to ensure its own consistency,security,scalablility,activity and finality.

3.2 Architecture of PoEC Consensus Process

PoEC architecture is to insert supervisory nodes into the supervised blockchain,which is composed of supervisory nodes and other types of nodes,to realize the supervision and review of the supervised blockchain,and implement the corresponding reward and punishment measures,as shown in Fig.2.In the figure,the leftmost block corresponds to supervisory blockchain network,which is generally an open public chain network where any node can issue intelligent contracts or transactions.The right-most block corresponds to a supervisory zone chain network,which is generally a licensed alliance chain network or a private chain network composed of representative nodes,various regulatory agencies,notaries or other stakeholders from the supervised blockchain.The supervisory node is deployed in both the supervisory blockchain network and the supervised blockchain network,and acts as the gateway node to realize cross-blockchain communication between the supervised blockchain and the supervised blockchain.Based on this architecture,the first aspect of functional requirements can be easily realized - supporting the supervisory chain to obtain the data of the supervised blockchain:N supervisory nodes are inserted into the supervised blockchain,and each supervisory node maintains the data of the whole public chain locally.Corresponding to the real-time monitoring function,when a new block is confirmed by the supervisory blockchain,supervisory nodes will broadcast it to the supervisory blockchain network.Corresponding to the function of active review,nodes in supervisory blockchain can issue data requests to supervisory nodes.Furthermore,due to the balance between scalability and efficiency,the amounts of supervisory nodes can be dynamically changed.

3.3 PoEC Consensus Process Description

As noted above,penalties can be specified in three categories:fines,trade bans,and frozen balances.From the perspective of consensus mechanism,the essence of realizing penalty is to force the supervised blockchain to accept certain transactions,while the essence of realizing prohibited transaction and frozen balance is to force the supervised blockchain not to accept certain transactions.The specific process of implementing the three punishment measures is as Fig.3.

Process 1.Synchronize lastest block.Each supervisory node synchronizes the lastest block of supervised blockchain into supervisory blockchain via the message(blockheight,block,nodeid),wherenodeidis the number of sender node.Bothblockheightandblockwill be accepted if the amounts of senders have reached trust threshold valuewheremis total amounts of supervisory nodes and[]is the operator rounding down.

Process 2.Supervisory consensus reached.After the lastest block of supervised blockchain is synchronized,supervisory blockchain reaches supervisory consensus(S_blockheight,S_block)based on whether Hotstuff,PBFT or other Byzantine algorithms,whereS_blockheightis the height of supervisory block andS_blockis the content of supervisory block.

Process 3.Send consensus to contracts.Each supervisory node synchronizes above consensus to supervised blockchain by sending consensus message(S_blockheight,S_block,nodeid)to Endorse Contracts in supervised blockchain.Endorse Contracts record the message and the consensus will be accepted once the amounts of senders have reached trust threshold valuen.

Process 4.Execute supervisory consensus.miners in supervised blockchain query the height and content of lastest supervisory consensus(S_blockheight,S_block)before executing and packaging normal transactions,the supervisory transactions inS_blockwill be executed and packaged preferentially and immediately whenS_blockheighthas been newly added.Algorithm 1 describes PoEC consensus.

Figure 3:Proof-of-Endorse-Contracts consensus mechanism

?

The above process is based on the following two assumptions:

Assumption 1.After the K block is confirmed by the public chain and before the K +1 block is generated,the supervisory node and the supervised blockchain can complete the process of crossblockchain,consensus and cross-blockchain.

Assumption 2.Based on the preset incentive mechanism,miners participating in this consensus process will receive corresponding remuneration,which may be gas fee or remuneration other than gas fee.This will ensure that the status of the communication contract in the regulatory block can be updated in the supervised blockchain.

There may be a doubt that if enforcing supervisory transactions will lead to hard branch because some miners may don’t accept the supervisory transactions enforced without sender’s private key.But the problem should be resolved primarily by relevant functional departments of governing blockchain by blockchain system,PoEC consensus mechanism is a hard fork protocol in fact.

4 Implementation Details of Endorse Smart Contacts

Endorse Smart Contacts are written in Solidity language,compiled and tested using Remix IDE,and local simulation is performed using JavaScript VM.Remix is convenient for users to write and execute smart contract code and provides a debugging and testing environment for solidity code.This section discusses implementation details.

There are three smart contracts are deployed on the blockchain,which are the node management contractPointManage,the address management contractAddressManage,and the block record contractBlockRecord.The entity relationship diagram of Endorse Smart Contacts are shown in Fig.4.

Figure 4:The contract entity relationship diagram of endorse smart contacts

4.1 PointManage Contract Details

ThePointManagecontract is responsible for the management of supervisory nodes list.It includes variables such as the contract owner addressowner,node address mappingpoints,and the total number of nodespoints_amount.It provides functions including node addition functionpoint_add,node deletion functionpoint_delete,node query functionpoint_search,and node total number functionamount.The Implementation details are shown in Tab.2.

Name Types Permission Describe points_amount Integer variable Public Total amounts of supervisory nodes points Mapping(integer variable to address variable)Public Number and address mapping of supervisory nodes point_add() Input:address variable Return:integer variable Only owner Add a new supervisory node point_search() Input:integer variable Return:address variable Public Search a supervisory node point_delete() Input:integer variable Only owner Delete a supervisory node

4.2 AddressManage Contract Details

TheAddressManagecontract is responsible for the management of the contract address.It mainly contains variables such as the node management contract addressPointManage_addand the block recording contract addressBlockRecord_add.The functions provided by it include the node management contract address setting functionset_pointmanage_addand query functionreturn_pointmanage_add,block recording contract address setting functionset_blockrecord_addand query functionreturn_blockrecord_add.The implementation details are shown in Tab.3.

Name Types Permission Describe PointManage_add Address variable Public Address of PointManage BlockRecord_add Address variable Public Address of BlockRecord set_pointmanage_add() Input:address variable Only owner Set PointManage_add return_pointmanage_add() Return:address variable Public Return PointManage_add set_blockrecord_add() Input:address variable Only owner Set BlockRecord_add set_blockrecord_add() Return:address variable Public Return BlockRecord_add

?

4.3 BlockRecord Contract Details

The Implementation details ofBlockRecordcontract are shown in Tab.4 and the algorithm ofblock_votes()is shown in Algorithm 2.

Table 4:Variables and functions of BlockRecord contract

Table 4:Continued

5 Experiments

5.1 Experiment Design and Settings

In this section,we evaluate whether PoEC consensus mechanism and Endorse Smart Contracts can meet the requirements of low cost,high scalability and being able to cross-blockchain.

For evaluating PoEC consensus mechanism,we simulated the blockchain network on a Windows 10 system with an I5 Intel Core CPU and 8 GB of RAM,which connected to governing blockchain by blockchain system based on the PoEC consensus mechanism proposed in Section 3.

In details of block settings,we set the average time for creating a blockBintervalto 12.42 s,the average block propagation delayBdelayto 6 s and the total simulation timeTsimto 2000 s.So the amounts of blocks we simulated in each period are around 160 while the amounts of main blocks are around 120.In details of transactions settings,we got the real data of transactions in Ethereum and fitting theGasLimit,GasUsedandGasPriceof simulated transaction byGaussianMixtureandRandomForestRegressorfunctions.For evaluating Endorse Smart Contracts,we firstly deployed Endorse Smart Contracts in Ethereum Ropsten(3)network by Remix IDE.Afterwards we respectively test the process of managing supervisory points and recording supervisory block.Finally we recorded the gas used of core functions by MetaMask extension of Google Chrome.

5.2 Experiment Results of PoEC Consensus Mechanism

The transactions in our simulation has two kinds,one of which is normal transaction generated in Ethereum and the other is supervisory transaction propagated from supervisory blockchain.The initial amounts of normal transactions is constantly 2000,and we gradually changed the ratio of supervisory transactions to normal transactions in[0,0.5]for steps in 0.05.

Defining the transaction delayTdelayas the average transaction delay that from being generated to being packaged of whole chain,we ran the simulation in 10 times and recorded an average value ofTdelay.Trends atTdelaycould reflect the scalability of PoEC consensus mechanism under the supervisory transactions increasing.Fig.5 plots the delay of supervisory transactionsSTdelay,normal transactionsNTdelayand total transactionsTTdelay,while Fig.6 plots the ratio that part of transactions delay to others.We can verify the scalability of PoEC consensus mechanism from two aspects as follows.

Figure 5:Transactions delay of three kinds in second,the blue one is NTdelay,the green one is TTdelay and the orange one is STdelay,with the ratio of supervisory transactions to normal transaction changed in[0,0.5]for steps in 0.05

Figure 6:Ratio of transactions delay,while NTdelay means normal transaction delay, STdelay means supervisory transactions delay and TTdelay means total transactions delay,with the ratio of supervisory transactions to normal transactions changed in[0,0.5]for steps in 0.05

Firstly,we can find in Fig.5 that the value ofSTdelayis always under 20 s while the value ofNTdelayhas a steady tendency from 80 s to 130 s,showing great scalability of supervisory transactions with the ratio of supervisory transactions to normal transactions increasing,because supervisory transactions is preferred packaged in PoEC consensus mechanismProcess 4.

Secondly,we can find in Fig.6 that the relative value ofSTdelayto total blockchain transactions,STdelay/TTdelay,sustains smaller than 30 percent with the ratio of supervisory transactions increasing,reflecting the scalability of our consensus as same as Fig.5.Otherwise,there may be a doubt that if PoEC could bring performance reduction to supervised blockchain.In fact,it depends on the amounts of supervisory transactions,in other words,the requirements of supervision.

5.3 Experiment Results of Endorse Smart Contracts

This part describes the cross-blockchain testing of the key functions of Endorse Smart Contacts,with the corresponding output log attached.For our test scenario,we deployed three smart contracts:AdressManage,BlockRecordandPointManage.Their address are“0xd9145CCE52D386f254917e481e B44e9943F39138”,“0xd8b934580fcE35a11B58C6D73aDeE468a2833fa8” and “0xf8e81D47203A59 4245E36C48e151709F0C19fBe8”respectively,which deployed by a same node,in other words,they belong a same owner whose address is “0x5b38da6a701c568545dcfcb03fcb875f56beddc4”.Most of the features we tested had one or more state requirements that we would not be able to use without meeting the requirements.

Testing 1.Points management.We assume that the supervised blockchain has deployed four supervisory nodes,which address are “0x5B38Da6a701c568545dCfcB03FcB875f56beddC4”,“0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2”,”0x4B20993Bc481177ec7E8f571ceCaE8A9e 22C02db”and”0x78731D3Ca6b7E34aC0F824c42a7cC18A495cabaB”respectively,while point numbers are 0,1,2 and 3 respectively.We use owner account of the contract to increase the fifth point,which address is“0x617f2e2fd72fd9d5503197092ac168c91465e7f2”and point number is 4,while the return value is the point number in contract,such as Fig.7.Then we inquired the point address with the point number 4,which was the same as the address entered before,as shown in Fig.8.This test uses thepoint_addfunction and thepoint_searchfunction in thePointManagecontract.

Figure 7:Transaction details of adding point by point_add

Figure 8:Transaction details of searching point by point_search

Testing 2.Block record.We continue the testing based on the previous content,and now five nodes have been deployed in the supervised blockchain,i.e.,point_amount=5.At the same time,we assume that three regulatory blocks have been recorded in the contract,with heights of 0,1 and 2 respectively.For testing purposes,we assign the contents of blocks to the string“This block has a height of 0”,“This block has a height of 1”and“This block has a height of 2”in UTF-8 encoding format respectively.Now we add a block with height of 3,which content is string“This block has a height of 3”.This test uses theblock_votesfunction and thegetnewblockfunction of theBlockRecordcontract.As a rule of majority,the new block is recorded in the smart contract if and only if the number of nodes sending the new block to the smart contract reaches 3.At the beginning of the test,until the third node votes,we use thegetnewblockfunction to query the current most recent block,and the return value is always a block of height 2,as shown in Fig.9.Then we use node No.4 to vote for the intelligent contract.This node is the third voting node,and the transaction details are shown in Fig.10.Then we use thegetNewBlockfunction again to query the current most recent block,and it is easy to see that it returns a block with a height of 3,as shown in Fig.11.

Figure 9:Transaction details of getting newest block by getnewblock

Figure 10:Transaction details of voting block by block_votes

Testing 3.Contract Cost.We deployed above contracts in Ropsten(3)network by Remix IDE and MetaMask and run some important functions,with recording the gas used overall process.The gas used and ether cost of each contract and function is shown in Tab.5,which has an advantage of low cost comparing with other solutions based on smart contract.

Figure 11:Transaction details of getting newest block by getnewblock

Table 5:Gas used and Ether cost of each contract and function

6 Summary and Future Work

Aiming at the application scenarios of supervision and governance,this paper proposes a crossblockchain consensus mechanism based on intelligent contract for chain governance.New consensus mechanism called Proof-of-Endorse-Contract (PoEC) consensus,which supports the supervisory blockchain to transfer the consensus reached to the smart contract in the supervised blockchain,and then the miners in the supervised blockchain will package and verify the new block according to the status of the smart contract.We introduce multiple digital signatures into the contract to ensure the security of cross-blockchain communication.PoEC protocol supports the regulated chain to join the chain regulation system without changing the original consensus mechanism,which has the advantages of low cost.

The experiments prove that our method can provide a feasible cross-blockchain governance scheme for the field of blockchain governance.To the best of our knowledge,our approach is the first to provide practical consensus solutions for governing blockchain by blockchain system and the first consensus mechanism to introduce smart contracts into consensus processes.This provides a basis for further applying machine learning and making the supervisors and supervised blockchain work easily,which are the subject of our future work.

Funding Statement:This work was supported by National Natural Science Foundation of China(Grant No.62162022 and 62162024),Key Projects in Hainan Province(Grant ZDYF2021GXJS003 and Grant ZDYF2020040),the Major science and technology project of Hainan Province(Grant No.ZDKJ2020012).

Conflicts of Interest:The authors declare that they have no conflicts of interest to report regarding the present study.