Designing secure indexes for encrypted databases

The conventional way to speedup queries execution is by using indexes. Designing secure indexes for an encrypted database environment raises the question of how to construct the index so that no information about the database content is exposed. In this paper, the challenges raised when designing a secure index for an encrypted database are outlined; the attacker model is described; possible attacks against secure indexes are discussed; the difficulty posed by multiple users sharing the same index are presented; and the design considerations regarding keys storage and encryption granularity are illustrated. Finally, a secure database-indexing scheme is suggested. In this scheme, protection against information leakage and unauthorized modifications is provided by using encryption, dummy values and pooling. Furthermore, the new scheme supports discretionary access control in a multi-user environment.