Efficient Provably-Secure Hierarchical Key Assignment Schemes

Abstract

A hierarchical key assignment scheme is a method to assign some private information and encryption keys to a set of classes in a partially ordered hierarchy, in such a way that the private information of a higher class can be used to derive the keys of all classes lower down in the hierarchy.In this paper we design and analyze hierarchical key assignment schemes which are provably-secure and support dynamic updates to the hierarchy with local changes to the public information and without requiring any private information to be re-distributed. We first show an encryption based construction which is provably secure with respect to key indistinguishability, requires a single computational assumption and improves on previous proposals. Then, we show how to reduce key derivation time at the expense of an increment of the amount of public information, by improving a previous result. Finally, we show a construction using as a building block a public-key broadcast encryption scheme. In particular, one of our constructions provides constant private information and public information linear in the number of classes in the hierarchy.