LOB: Bucket Based Index for Range Queries

Database-as-a-service is a promising data management paradigm in which data is encrypted before being sent to the untrusted server. Efficient querying on encrypted data is a performance critical problem which has various solutions, among which bucket based index is an effective and flexible one. In previous research some metrics are proposed to measure security and efficiency. In this paper, we illustrate by example the limitations of these metrics and introduce a new security metric based on probability distribution variance and efficiency metric based on overlapping ratio. Based on these metrics we propose a local overlapping bucket algorithm (LOB) with time complexity of O(nlogn), where n represents the cardinality of the table. Experiments on synthetic and real dataset show that our algorithm can achieve higher security by trading off efficiency.