Decentralized attribute-based encryption (ABE) is a variant of multi-authority based ABE whereby any attribute authority (AA) can independently join and leave the system without collaborating with the existing AAs. In this paper, we propose a user collusion avoidance scheme which preserves the user's privacy when they interact with multiple authorities to obtain decryption credentials. The proposed scheme mitigates the well-known user collusion security vulnerability found in previous schemes. We show that our scheme relies on the standard complexity assumption (decisional bilienar Deffie-Hellman assumption). This is contrast to previous schemes which relies on non-standard assumption (q-decisional Diffie-Hellman inversion).

Technology advancements in smart mobile devices empower mobile users by enhancing mobility, customizability and adaptability of computing environments. Mobile devices are now intelligent enough to capture dynamic attributes such as unlock failures, application usage, location and proximity of devices in and around its surrounding environment. Different users will have different set of values for these dynamic attributes. In traditional attribute based access control, users are authenticated to access restricted data using long term static attributes such as password, roles, and physical location. In this paper, in order to allow secure data access in mobile environment, we securely combine both the dynamic and static attributes and develop novel access control technique. Security and performance analyse show that the proposed scheme substantially reduces the computational complexity while enhances the security compare to the conventional schemes.