PTA-SC: Privacy-Preserving Task Allocation for Spatial Crowdsourcing

Spatial crowdsourcing (SC) is a popular type of crowdsourcing, in which all tasks are associated with locations/regions. Given an SC task, only the participants in the specified location/region are allowed to submit their answers of the task. However, outsourcing the SC tasks to a remote crowdsourcing server poses new security concerns. For example, the task requester may not want to disclose the task content to unauthorized users, and the participants may not want to disclose their locations to untrusted server. To address these issues, we propose a Privacy-Preserving Task Allocation for Spatial Crowdsourcing (PTA-SC) scheme in this paper. In PTA-SC, regions and locations can be encoded into a set of prefixes based on the prefix encoding method. The location-induced prefixes are treated as attributes and the region-induced prefixes are used to generate an access policy tree for a ciphertext-policy attribute-based encryption (CP-ABE) scheme. PTA-SC can check whether a location is inside an SC task region by evaluating if the attributes satisfy the access policy tree or not. Our theoretical analysis shows that PTA-SC can achieve location privacy preservation and task privacy preservation. Through experiments, we show that PTA-SC scheme can realize adaptive region representation accuracy control and high-efficiency.