MFSSE: Multi-Keyword Fuzzy Ranked Symmetric Searchable Encryption With Pattern Hidden in Mobile Cloud Computing

In mobile cloud computing, efficient multi-keyword Symmetric Searchable Encryption (SSE) enables low power terminal devices to search encrypted data from the cloud. However, a large number of search requests can lead to the privacy of search information and encrypted data being leaked to the cloud servers, such as, the cloud server can can predict whether two keywords are consistent in multiple searches (i.e., search patterns leakage), and what keywords are contained in an encrypted file (i.e., access pattern leakage). In this paper, we propose a novel Multi-keyword Fuzzy SSE with patterns hidden, namely MFSSE. In MFSSE, the search trapdoor can be modified differently each time even if the keywords are the same when performing multi-keyword search to prevent the leakage of search patterns. Moreover, MFSSE modifies the search trapdoor by introducing random false negative and false positive errors to resist access pattern leakage. Furthermore, MFSSE utilizes efficient cryptographic algorithms (e.g., Locality-Sensitive Hashing) and lightweight operations (such as, integer addition, matrix multiplication, etc.) to minimize computational and communication, and storage overheads on mobile devices while meeting security and functional requirements. Specifically, its query process requires only a single round of communication, in which, the communication cost is linearly related to the number of the documents in the database, and is independent of the total number of keywords and the number of queried keywords; its computational complexity for matching a document is O(1) ; and it requires only a small amount of fixed local storage (i.e., secret key) to be suitable for mobile scenarios. The experimental results demonstrate that MFSSE can prevent the leakage of access patterns and search patterns, while keeping a low communication and computation overheads.