Encrypted Search Algorithm For P2P Storage System Based On Blockchain

In recent years,massive data is growing explosively.It is very necessary to build a safe and reliable platform for trading data which can interconnect a large amount of idle space to meet the growing storage needs from people.Although P2 P systems are regarded as ideal models for building distributed and large-scale storage systems,P2 P systems are notorious due to its lack of secure incentive mechanism to guarantee a fair trade.Until the rise of blockchain,a brand-new P2 P system has been brought.Through this platform,the servers can be inspired to provide resources,and users can be enforced to pay honestly.However,there are still several problems in blockchain-based P2 P storage system,such as the lack of effective search ability for encrypted data,huge overhead from updating data and the inability to verify the query results.Therefore,how to realize the encrypted search and effective verification about data in the blockchain-based P2 P storage system is a problem to be solved urgently in the current research.Though the application of searchable symmetric encryption(SSE)can effectively protect user privacy and avoid information leakage in P2 P storage systems,the great majority of SSE schemes adopts static solutions where file update cannot be supported.Meantime,they do not consider the forward security of the system after updating,so that malicious servers often use file injection attacks to illegally obtain private data that seriously damages the rights and interests of users.Therefore,in the blockchain-based P2 P storage system,how to design an effective encrypted search scheme to solve the dynamic update and forward security is still a challenge.To address these problems,a safe and effective blockchain-based P2 P storage system which uses blockchain technology is built at first in the thesis.Based on the designed system,a searchable encryption scheme is proposed to connect users with storage needs and servers with free space effectively.The system can ensure the fairness and reliability of the service by verifying the correctness and completeness of the query results and realize a highly secure and efficient encrypted search.In order to solve the problems of dynamic update and forward security,this thesis further proposes an encrypted search algorithm that supports dynamic file updates and guarantees forward security based on the blockchain-based P2 P storage system.Our algorithm adopts a dual index structure.By adding a file index and a keyword index to the index chain in the meantime,it balances theefficiency of search and update and achieves fast file updates effectively.To ensure forward security,that means newly added documents cannot be linked to previously searched keywords,this thesis introduces random numbers in each result set and always uses a new random mask to generate a new index to link to the head of the original index chain,thus this way can effectively prevent file injection attacks.In order to verify the query results,this thesis also proposes a new verification scheme.By pre-defining an encrypted verification table in the blockchain that contains several hash values of results,the overhead of the blockchain is effectively reduced and powerful data protection is achieved.Finally,according to the security concept of dynamic searchable symmetric encryption,the detailed security definition of our system is given and the security of the proposed system are proved in theory.Besides,the prototype of our system is implemented and smart contract is successfully deployed on Ethereum blockchain.Through a large number of performance evaluation and comparative analysis,the experimental results prove that our design can be applicable to a blockchain-based P2 P storage system and achieves a secure,verifiable and efficient encryption search.