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Space-optimized Implementation of a Database Obfuscator for Group Privacy

Privacy of data concerns data owners, customers, and marketers. Breaches in privacy populate headlines frequently, including one case where ID numbers and contact information of Hong Kong citizens who complained about the police in the past five years were exposed on the Internet [11]. The research community has proposed data privacy protection through statistical data randomization [1, 5], query auditing [10], secure multi-party computation [9], and private information retrieval [4]. We would like to protect the data differently by making imprecise queries to a database computationally infeasible to evaluate. In other words, we restrict allowed accesses to the database to those that should be computed quickly. We can do this through obfuscation, which effectively moves access control into the target database, allowing database owners to release the database knowing that only precise queries can be evaluated efficiently, depending exponentially on the number of records that would satisfy the query. Thus, access becomes non-interactive–the owner or any trusted party does not have to oversee or approve every query submitted by the database user. Legal accesses are embodied by the owner-specified access/privacy policy, which describes the ideal functionality of the obfuscated database by specifying which queries can be satisfied efficiently. Ideal functionality is an abstraction that allows us to decide whether the obfuscator is secure [7]. We can imagine a trusted third party who provides the ideal functionality by filtering all accesses from a simulator. We will consider our construction secure if an attacker’s actions can be emulated by this simulator and trusted third party. Because our construction leaks meta information about the content of the database, we work with a weaker notion of obfuscation than a ”virtual black box” [2]. The construction is still useful because the leakage does not compromise the security of access control, which is our primary focus.