User-Friendly Field-Free Multikeyword Searchable Certificateless Encryption With Keyword Guessing Attack Security

Searchable public key encryption (SPKE) is a beneficial supplement to traditional public key encryption, which offers a viable method to address the retrieval issue over enciphered data. As a development of SPKE, searchable certificateless encryption enjoys good features of no burdensome certificate management and no key escrow. However, existing searchable certificateless encryption schemes suffer some limitations. Some only support single-keyword search, which often yields inaccurate results. Others enable conjunctive keyword search, which is difficult to cope with data lacking unified keyword fields. In the work, we present a user-friendly certificateless authenticated encryption with field-free multi-keyword search scheme. The proposed scheme eliminates time-consuming operations like bilinear pairing and hash-to-point calculations for data owners and data users. It also enables data users to make multi-keyword searches flexibly on resource-limited mobile devices without concern for keyword orders or positions. As far as we know, it is the first certificateless encryption scheme that supports field-free multi-keyword search. We demonstrate that it has the keyword guessing attack security by formal proofs and show its superior performance by comparisons and experiments. Compared to the state-of-the-art scheme with field-free multi-keyword search, our scheme reduces computation cost for creating a search token and communication cost for sending the search token by about 60% and 56%, respectively.