MMKFB: multi-client and multi-keyword searchable symmetric encryption with forward and backward privacy

Data outsourcing has become an industry trend with the popularity of cloud computing. How to search data securely and efficiently has received unprecedented attention. Dynamic Searchable Symmetric Encryption (DSSE) is an effective method to solve this problem, which supports file updates and keyword-based searches over encrypted data. Unfortunately, most existing DSSE schemes have privacy leakages during the addition and deletion phases, thus proposing the concepts of forward and backward privacy. At present, some secure DSSE schemes with forward and backward privacy have been proposed, but most of these DSSE schemes only achieve single-keyword query in the single-client setting, which seriously limits the application in practice. To solve this problem, we propose a multi-client and multi-keyword searchable symmetric encryption scheme with forward and backward privacy (MMKFB). Our scheme focuses on the multi-keyword threshold queries in the multi-client setting, which is a new pattern of multi-keyword search realized with the help of additive homomorphism. And performance analysis and experiments demonstrate that our scheme is more practical for use in small and medium size databases. Especially when a large number of files are updated at once, our scheme has advantages over some existing DSSE schemes in terms of computational efficiency and client storage overhead.