In this paper we design and analyze time-bound hierarchical key assignment schemes which are provably-secure and efficient. We consider both the unconditionally secure and the computationally secure settings and distinguish between two different goals: security with respect to key indistinguishability and against key recovery. We first present definitions of security with respect to both goals in the unconditionally secure setting and we show tight lower bounds on the size of the private information distributed to each class. Then, we consider the computational setting and we further distinguish security against static and adaptive adversarial behaviors. We explore the relations between all possible combinations of security goals and adversarial behaviors and, in particular, we prove that security against adaptive adversaries is (polynomially) equivalent to security against static adversaries. Afterwards, we prove that a recently proposed scheme is insecure against key recovery. Finally, we propose two different constructions for time-bound key assignment schemes. The first one is based on symmetric encryption schemes, whereas, the second one makes use of bilinear maps. Both constructions support updates to the access hierarchy with local changes to the public information and without requiring any private information to be re-distributed. These appear to be the first constructions for time-bound hierarchical key assignment schemes which are simultaneously practical and provably-secure.
Category / Keywords: Access control, key assignment, provable security Publication Info: A preliminary version of this paper appears in the proceedings of ACM CCS 2006. Date: received 3 Jul 2006, last revised 4 Jan 2007 Contact author: masucci at dia unisa it Available formats: Postscript (PS) | Compressed Postscript (PS.GZ) | PDF | BibTeX Citation Version: 20070104:143930 (All versions of this report) Discussion forum: Show discussion | Start new discussion