A performance tunable CPIR-based privacy protection method for location based service

Location-based service has become one of the essential parts of our daily lives, which raises a problem: how to preserve location privacy. Computational Private Information Retrieval (CPIR) protocol, which does not need a trusted third party, allows users to retrieve data from a service provider without revealing users' query information. However, the CPIR protocol scans the entire data space, which causes high costs and limits the scale of CPIR-based applications. To address this problem, we propose a performance tunable Computational Private Information Retrieval (PTCPIR) model. We divide data space into subspaces and scan a subset of subspaces to achieve better performance while sacrificing some privacy. By tuning the percentage of scanned subspaces, we can achieve a tradeoff between performance and privacy. We design a hierarchical encrypted secure index to support data users to retrieve subspace information safely and efficiently, which facilitates privacy-preserving subspace information retrieval. Furthermore, we propose a novel subspace information retrieval method where the confused query keyword sequence makes servers unable to count query probability. Hence access pattern privacy is protected. Experiments on Sequoia and synthetic datasets demonstrate that our PTCPIR model provides a tunable tradeoff between performance and privacy with high efficiency and good scalability.