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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Symmetric searchable encryption (SSE) enables users to search the ciphertext stored on the untrusted cloud without revealing the search keywords, effectively protecting users' privacy. However, most of the existing SSE schemes reveal the search or access pattern during the keyword query, which can be used by the adversary to infer the sensitive information in ciphertext, thus posing a great threat to users' privacy. To address this, we propose an SSE scheme supporting search pattern and access pattern protection in multi-cloud, called SAPM-SSE. In our scheme, an index shuffle protocol is proposed to change the content and location of the index after each query, which helps to achieve the protection of search and access pattern. Furthermore, with the purpose of improving the efficiency of shuffling, we construct a shuffling algorithm based on index cache, the number of index entries for shuffling reduced from γ to γ/n (n≥1).Besides, our scheme supports the dynamic update of documents and achieves the forward security in update. Finally, security analysis and experimental results show that our scheme can achieve the protection of search pattern and access pattern with high efficiency.