Efficient privacy-aware search over encrypted databases

Abstract

In recent years, database as a service (DAS) model where data management is outsourced to cloud service providers has become more prevalent. Although DAS model offers lower cost and flexibility, it necessitates the transfer of potentially sensitive data to untrusted cloud servers. To ensure the confidentiality, encryption of sensitive data before its transfer to the cloud emerges as an important option. Encrypted storage provides protection but it complicates data processing including crucial selective record retrieval. To achieve selective retrieval over encrypted collection, considerable amount of searchable encryption schemes have been proposed in the literature with distinct privacy guarantees. Among the available approaches, oblivious RAM based ones offer optimal privacy. However, they are computationally intensive and do not scale well to very large databases. On the other hand, almost all efficient schemes leak some information, especially data access pattern to the remote servers. Unfortunately, recent evidence on access pattern leakage indicates that adversary's background knowledge could be used to infer the contents of the encrypted data and may potentially endanger individual privacy. In this paper, we introduce a novel construction for practical and privacy-aware selective record retrieval over encrypted databases. Our approach leaks obfuscated access pattern to enable efficient retrieval while ensuring individual privacy. Applied obfuscation is based on differential privacy which provides rigorous individual privacy guarantees against adversaries with arbitrary background knowledge.