Verifying spatial queries using Voronoi neighbors

With the popularity of location-based services and the abundant usage of smart phones and GPS enabled devices, the necessity of outsourcing spatial data has grown rapidly over the past few years. Nevertheless, in the database outsourcing paradigm, the authentication of the query results at the client remains a challenging problem. In this paper, we focus on the Outsourced Spatial Database (OSDB) model and propose an efficient scheme, called VN-Auth, that allows a client to verify the correctness and completeness of the result set. Our approach can handle both k nearest neighbor (kNN) and range queries, and is based on neighborhood information derived by the Voronoi diagram of the underlying spatial dataset. Specifically, upon receiving a query result, the client can verify its integrity by examining the signatures and exploring the neighborhood of every object in the result set. Compared to the current state-of-the-art approaches (i.e., methods based on Merkle hash trees), VN-Auth produces significantly smaller verification objects (VO) and is more computationally efficient, especially for queries with low selectivity.