Searchable symmetric encryption (SSE) provides an effective way to search encrypted data stored on untrusted servers. When the server is not trusted, it is indispensable to verify the results returned by it. However, the existing SSE schemes either lack fairness in the verification of search results, or do not support the verification of multiple keywords. To address this, we designed a multi-keyword verifiable searchable symmetric encryption scheme based on blockchain, which provides an efficient multi-keyword search and fair verification of search results. We utilized bitmap to build a search index in order to improve search efficiency, and used blockchain to ensure fair verification of search results. The bitmap and hash function are combined to realize lightweight multi-keyword search result verification, compared with the existing verification schemes using public key cryptography primitives, our scheme reduces the verification time and improves the verification efficiency. In addition, our scheme supports the dynamic update of files and realizes the forward security in update. Finally, formal security analysis proves that our scheme is secure against Chosen-Keyword Attacks (CKA), experimental analysis demonstrations that our scheme is efficient and viable in practice.

In cloud storage scenarios, data security has received considerably more attention than before. To ensure the reliability and availability of outsourced data and improve disaster resilience and data recovery ability, important data files possessed by users must be stored on multiple cloud service providers (CSPs). However, we know that CSP is invariably not reliable. In this situation, to verify the integrity of replica files stored by users on multiple CSPs simultaneously, a new dynamic multiple-replica provable data possession (DMR-PDP) scheme is proposed. In addition, due to the importance of the tag set, we utilize vector dot products instead of using the modular power calculation in the traditional PDP scheme, which greatly reduces the calculation time and storage space usage. Moreover, a novel dynamic data structure, the divided addressversion mapping table (DAVMT), is presented and used to solve the problem of data dynamic operation. A practical experiment validates the effectiveness of our proposed scheme in the end. INDEX TERMS Cloud storage, data security, provable data possession, dynamic operation.

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Under the cloud computing environment, Searchable Symmetric Encryption (SSE) is an effective method to solve the problem of encrypted data retrieval, and helps to protect the users' privacy. Recent researches show that some attacks may bring great security threats to SSE, and forward privacy can effectively prevent these attacks, so forward privacy is very necessary for SSE scheme. Most of the existing forward privacy SSE schemes fall into two types: ORAM-based and Bost-based. The former is simple, but it has large communication overhead and low dynamic update efficiency. The latter is better than the former, but it is based on asymmetric encryption primitives. Based on symmetric encryption primitives, we propose a dynamic efficient forward privacy scheme DESSE in this paper. DESSE uses pseudo-random permutation to realize forward privacy, and uses delete list to identify the final state of the same file added and deleted repeatedly, so as to realize the dynamic update of data. The method proposed in this paper is simple and flexible in structure, takes up less additional space, and can significantly improve the efficiency of updating. At the same time, it can achieve real-time updating of data. The correctness of our proposed scheme is tested using the Enron email data set in the end.