Intertwining Order Preserving Encryption and Differential Privacy
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Ciphertexts of an order-preserving encryption (OPE) scheme preserve the order of their corresponding plaintexts. However, OPEs are vulnerable to inference attacks that exploit this preserved order. At another end, differential privacy has become the de-facto standard for achieving data privacy. One of the most attractive properties of DP is that any post-processing (inferential) computation performed on the noisy output of a DP algorithm does not degrade its privacy guarantee. In this paper, we intertwine the two approaches and propose a novel differentially private order preserving encryption scheme, OPϵ. Under OPϵ, the leakage of order from the ciphertexts is differentially private. As a result, in the least, OPϵ ensures a formal guarantee (specifically, a relaxed DP guarantee) even in the face of inference attacks. To the best of our knowledge, this is the first work to intertwine DP with a property-preserving encryption scheme. We demonstrate OPϵ's practical utility in answering range queries via extensive empirical evaluation on four real-world datasets. For instance, OPϵ misses only around 4 in every 10K correct records on average for a dataset of size ∼732K with an attribute of domain size ∼18K and ϵ= 1.
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