Keyword-Field-Free Conjunctive Searchable Encryption for Multiuser in EMR System

In electronic medical record (EMR) systems, numerous EMRs are usually uploaded to cloud servers for storage and data sharing. Public key authenticated encryption with keyword search (PAEKS) which can resist keyword guessing attacks (KGAs) provides a feasible approach for data sharing and searching in EMR systems. Specifically, a PAEKS scheme requires the sender to use the receiver’s public key when encrypting, which restricts the generated ciphertext to be searchable by only one specified receiver. If a sender wants to share a data with multiple receivers, the sender has to repeatedly encrypt the data for multiple receivers using the public keys of different receivers. For the receiver, the same issue also exists in the trapdoor generation phase. Therefore, the traditional PAEKS is not suitable for EMR systems involving multiple senders and multiple receivers because of a large number of repeated computations. In this work, we present a practical scheme called multiuser keyword-field-free conjunctive searchable encryption (MU-KFFCSE). In order to achieve KGA-resistant searchable encryption between senders and receivers, we use receiver servers and sender servers such that the computation cost and communication cost of the ciphertext (trapdoor) generation phase are independent of the number of receivers (senders). The proposed scheme also supports flexible searchable encryption with keyword-field-free conjunctive utilizing polynomial technology, which not only increases the accuracy of search results, but also eliminates the limitation of fields. We prove that our scheme satisfies ciphertext indistinguishability (CI) and trapdoor indistinguishability (TI) security without random oracle. Theoretical analysis and experimental results show that our scheme is efficient in terms of computation cost and storage cost compared with existing schemes.