Fine-grained search and access control in multi-user searchable encryption without shared keys

Searchable encryption schemes enable secure sharing and efficient retrieval of encrypted documents stored in the cloud. Multi-user symmetric searchable encryption allows multiple users to upload encrypted data to the cloud and selectively authorize other people to search and retrieve documents without revealing any information about either the search query or sensitive information. This however, poses major challenges since it involves managing the access control policies of a set of users by a third party. Selectively sharing files among an arbitrary set of users is more challenging than allowing all members of a group to access a set of documents. The proposed scheme ensures that the search returns only those documents that are accessible to the querier and guarantees that only authorized users are allowed to decrypt a document. A bilinear map accumulator combined with pairing based cryptography ensures that only authorized users can decrypt a shared document. Prior schemes have addressed the problem using shared keys or by using trusted third parties. The proposed scheme supports both keyword searches and selective sharing of data among multiple users in the cloud without requiring shared keys or trusted third parties. The security of our scheme is proved using rigorous security analysis.