Preserving Location Privacy for Outsourced Most-Frequent Item Query in Mobile Crowdsensing

The emergence of mobile crowdsensing (MCS) has provided us with unprecedented opportunities for both sensing coverage and data transmission. However, in many MCS applications, the MCS workers are usually required to report the location information of the assigned tasks, which inevitably reveals the workers' location information, even trajectories, and severely impedes the popularization of the MCS system. It is believed that the query on the most-frequent location, e.g., querying the most congested location over a period in a city, is one of the most popular statistics queries in the MCS system, but it may disclose workers' location information. To address the issue, in this article, we propose a location privacy-preserving scheme for outsourced most-frequent item query in the MCS system, where two noncollusive semi-trusted cloud servers cooperatively handle the most-frequent item query. Specifically, by employing our pseudonymization mechanism, transposition cipher, ciphertext packing technique, and order-preserving merge function, our proposed scheme can efficiently answer the most-frequent item query while ensuring the privacy of both workers' personal information and query results. Detailed security analysis shows that our proposed scheme is privacy-preserving. In addition, extensive experiments are conducted, and the results show that our proposed scheme outperforms alternative schemes in terms of computational costs and communication overhead.