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The Blind Enforcer: On Fine-Grained Access Control Enforcement on Untrusted Clouds

Migration of one’s computing infrastructure to the cloud is gathering momentum with the emergence of relatively mature cloud computing technologies. As data and computation are being outsourced, concerns over data security (such as confidentiality, privacy and integrity) remain one of the greatest hurdles to overcome. In the meanwhile, the increasing need for sharing data between or within cloud-based systems (for instance, sharing between enterprise systems or users of a social network application) demands even more care in ensuring data security. In this paper, we investigate the challenges in outsourcing access control of user data to the cloud. We identify what constitute a finegrained cloud-based access control system and present the design-space along with a discussion on the current state-of-the-art. We then describe a system which extends an Attribute-Based Encryption scheme to achieve more fine-grainedness as compared to existing approaches. Our system not only protects data from both the cloud service provider and unauthorized access from other users, it also moves the heavy computations towards the cloud, taking advantage of the latter’s relatively unbounded resources. Additionally, we integrate an XML-based framework (XACML) for flexible, high-level policy management. Finally, we discuss some open problems, solving which would lead to a further robust and flexible cloud-based access control system.