Secure And Efficient Data Sharing Scheme Based On Blockchain

With the development of electronic information technology,the contradiction between data sharing and data security is becoming more and more prominent.How to ensure the data is not tampered with or leaked has become a problem to be solved urgently.The blockchain is decentralization and publicly verifiable so that it can solve the problem well with proper security policy,and produce a marked effect in the face of lightweight data or heavyweight data.Electronic medical records(EMR)have been a common way to store the patients' data in hospitals.They are stored in different hospitals' databases,even for the same patient.Therefore,it is difficult to construct a summarized EMR for one patient from multiple hospital databases due to the security and privacy concerns.Meanwhile,current EMR systems lack a standard data management and sharing policy,making it difficult for pharmaceutical scientists to develop precise medicines based on data obtained under different policies.To solve the above problems,we proposed a blockchain-based information management system,MedBlock,to handle patients' information.In this scheme,heavyweight raw medical data is stored in local database or cloud,and summary information is recorded in the ledger.The distributed ledger of MedBlock allows the efficient EMR access and EMR retrieval.The improved consensus mechanism achieves consensus of EMR without large energy consumption and network congestion.In addition,MedBlock also exhibits high information security combining the customized access control protocols and symmetric cryptography.MedBlock can play an important role in the sensitive medical information sharing.Internet of Things(IoT)has been developed rapidly to make our life easier.In many IoT applications(e.g.,smart homes,healthcare,etc.),all the IoT devices should be synchronized in time.However,some malicious nodes located in the IoT network can influence the time synchronization,which may interrupt the IoT system and lead to serious accidents.Therefore,it is critical and challenging to guarantee the accuracy and consistency of time during the time synchronization among all the IoT devices.In this thesis,we propose a blockchain-based scheme to assure the security during time synchronization in IoT.Specifically,time data is a lightweight data.Publicly verifiable ledger is utilized to record and broadcast time,which can minimize many attacks from external environments.The use of multiple time sources can avoid the vulnerabilities caused by the centralized generation of accurate time.Moreover,the decentralized structure of this scheme has the advantage of adapting the changes of network topology.By employing an improved Practical Byzantine Fault Tolerance(PBFT)consensus mechanism,time synchronization can be implemented efficiently.At last,the analysis results show that our proposed scheme can achieve the desired security with high efficiency.This thesis focuses on blockchain-based secure and efficient data sharing schemes.And we propose two schemes to solve the practical difficulties in the medical field and the Internet of Things.How to make full use of the characteristics of blockchain to achieve privacy preserving and data sharing has become a very hot research direction.