Abstract

This work presents the design, analysis and implementation of the first sub-linear searchable symmetric encryption (SSE) protocol that supports conjunctive search and general Boolean queries on symmetrically-encrypted data and that scales to very large data sets and arbitrarilystructured data including free text search. To date, work in this area has focused mainly on single-keyword search. For the case of conjunctive search, prior SSE constructions required work linear in the total number of documents in the database and provided good privacy only for structured attribute-value data, rendering these solutions too slow and inflexible for large practical databases. In contrast, our solution provides a realistic and practical trade-off between performance and privacy by efficiently supporting very large databases at the cost of moderate and welldefined leakage to the outsourced server (leakage is in the form of data access patterns, never as direct exposure of plaintext data or searched values). A key aspect of our protocols is that it allows the searcherto pivot its conjunctive search on the estimated least frequent keywordin the conjunction. We show that a decisional Diffie-Hellman (DDH) based pseudo-random function