Secure Range Queries for Multiple Users

Order-preserving encryption allows encrypting data, while still enabling efficient range queries on the encrypted data. Moreover, it does not require any change to the database management system, because comparison operates on ciphertexts as on plaintexts. This makes order-preserving encryption schemes very suitable for data outsourcing in cloud computing scenarios. However, all order-preserving encryption schemes are necessarily symmetric limiting the use case to one client and one server. Imagine a scenario where a Data Owner encrypts its data before outsourcing it to the Cloud Service Provider and a Data Analyst wants to execute private range queries on this data. This scenario occurs in many cases of collaborative machine learning where data source and processor are different entities. Then either the Data Owner must reveal its encryption key or the Data Analyst must reveal the private queries. In this paper, we overcome this limitation by allowing the equivalent of a public-key order-preserving encryption. We present a secure multiparty protocol that enables secure range queries for multiple users. In this scheme, the Data Analyst cooperates with the Data Owner and the Cloud Service Provider in order to orderpreserving encrypt the private range queries without revealing any other information to the parties. The basic idea of our scheme is to replace encryption with a secure, interactive protocol. In this protocol, we combine order-preserving encryption based on binary search trees with homomorphic encryption and garbled circuits achieving security against passive adversaries with sublinear communication and computation complexity. We apply our construction to different order-preserving encryption schemes including frequency-hiding order-preserving encryption which can withstand many of the popularized attacks on orderpreserving encryption. We implemented our scheme and observed that if the database size of the Data Owner has 1 million entries it takes only about 0.3 s on average via a loopback interface (1.3 s via a LAN) to encrypt an input of the Data Analyst.