Joins Over Encrypted Data with Fine Granular Security

Performing joins over encrypted data is particularly challenging, since the query result or access pattern of 1 : n-joins reveals the frequency of each distinct element in the column. This frequency information is used in many easy, but very detrimental inference attacks. In this paper we present a different approach: Instead of implementing a stand-alone join operator that reveals the frequency of each element in the column, we show how to construct joins over encrypted data after selection operations have been applied. These joins only leak the fine granular access pattern and frequency of elements selected for the join. Our new fine-granularly secure joins use searchable encryption and key-policy attribute-based encryption and support dynamically adding and removing database rows. Their performance is practical and we present an implementation in MySQL.