A blockchain-based dynamic searchable symmetric encryption scheme under multiple clouds

In data outsourcing services, to ensure data security and user privacy, data is usually stored in cloud servers in ciphertext form. This method makes users face the problem of how to search the keywords in the ciphertexts. Although the Dynamic Searchable Symmetric Encryption (DSSE) schemes can solve this problem, most DSSE schemes assume that all the data is stored in a single cloud server. The assumption is not realistic since data may be stored in multiple servers. Furthermore, the cloud servers are usually considered “honest-but-curious”, though malicious servers can actively attack and return incomplete or incorrect results. In this paper, we propose a Blockchain-based DSSE under the Multiple Clouds (BDSSE-MC) scheme. The scheme enables the data owner to generate encrypted local file indexes and merges the local indexes into a global index through a smart contract. The search operation is also performed by the smart contract based on the global index. In this scheme, the attacker cannot obtain the original files and search results, only knows the number of clouds and the number of files. We provide security and privacy analysis. We also compare the experiments results with those of traditional solutions.