Conjunctive multi-key searchable encryption with attribute-based access control for EHR systems

With the growing demands of online access to health services, multiple medical institutions store their encrypted electronic health records (EHR) on the cloud and share them with the specified doctors and researchers. Multikey searchable encryption (MKSE) is very suitable for this case for the sake of the privacy of patients and the system effeciency. In MKSE, multiple data owners can encrypt the data with their own secret keys and upload them to the remote cloud server. In order to search all the encrypted data on the cloud for a keyword, an authorized user only needs to generate a single trapdoor whose length is independent on the number of the data owners. MKSE allows multiple data owners to share their data with users efficiently. In this paper, we present an efficient MKSE scheme which supports fine-grained access control and conjunctive keyword searches. Both the control policy and keyword expressivity of our scheme are more flexible than the existing MKSE schemes. Meanwhile, our scheme can resist the keyword guessing attack. We will simulate our MKSE scheme and show that it is practical in the real world applications.