Privacy preserving fine-grained location-based access control for mobile cloud.

Mobile cloud computing is a revolutionary computing paradigm for mobile applications, which enables storage and computation migration from mobile users to resource-rich and powerful cloud servers. This migration causes some privacy issues in providing secure data storage, fine-grained access control and anonymity of users. Attribute-based encryption is an end-to-end public key encryption mechanism that ensures security of stored data in the cloud and provides fine-grained access control using defined policies and constraints. Location of a device is one of the contextual policies, which is used to improve data security, authenticate user and provide access to services and useful information. However, unlike other policies and attributes used in attribute-based encryption, location attribute is an intrinsic dynamic attribute. In this paper, we investigate providing Location-Based Services (LBSs) for attribute-based access control in mobile cloud. More specifically, we propose a multi-authority attribute-based access control scheme to support coexistence of authorities, provide anonymity of users and protect their identity against malicious authorities. The proposed scheme uses dynamic location of mobile users as contextual information about those users, employs location range constraints as a policy in attribute-based encryption and authorizes users with dynamic locations satisfying access policies. The proposed attribute-based encryption is integrated with proxy re-encryption to (a) transform secret information received from different authorities and protect users' identities from disclosure to cloud server, and (b) outsource the computation to a cloud server with unlimited computational power. This results in achieving more efficiency and reducing the computation cost on resource-constrained mobile users.