Ranked Searchable Encryption Based On Differential Privacy And Blockchain

Ranked search allows the cloud server to search the top-k most relevant documents according to the relevance score between query keyword and documents,which has been recognized as one of the most promising ways to realize secure search over the encrypted database.However,recent studies show that some privacy protection methods commonly used in ranked search,like order-preserving encryption(OPE),have some security problems.These problems may lead to the leakage of the relevant ranked privacy information.In addition,considering that data is an important factor in production,promoting paid queries has also become a research hotspot.Meanwhile,most of the existing ranked searchable encryption schemes are used in cloud environment scenarios and they do not consider the problem of fair payment in outsourced services.A malicious server may return a wrong search result to the user after receiving the service fee,and a malicious user may deliberately slander the service provider after obtaining the correct result.To solve the above problems,this paper proposes two schemes:(1)We propose a scheme,called privacy-preserving ranked searchable encryption based on differential privacy(DP-RSE).Specifically,we add noise drawn from Laplace distribution into the relevance score to disturb its value.In this way,no matter how much background the adversary has,he cannot obtain the true relevance score or ranked order.Moreover,the experiment results show that the scheme can achieve sub-linear efficiency and the accuracy of search results can reach 94%.(2)Aiming at the phenomenon of unfair payment in the cloud environment,based on the first scheme,we propose a blockchain-based ranked searchable encryption that can realize fair payment and verifiability.We first design a verification index and then store it in the smart contract to verify the correctness of the results returned by the cloud server.At the same time,the automatic execution feature of the smart contract is used to ensure that as long as the service provider and the user execute the agreement honestly,they can get the deserved results.Meanwhile,all operations and operating results can be publicly verified and traced in the blockchain.