How to design space efficient revocable IBE from non-monotonic ABE

Abstract

Since there always exists a possibility that some users' private keys are stolen or expired in practice, it is important for identity based encryption (IBE) system to provide a solution to revocation. The current most efficient revocable IBE system has a private key of size O(log ns) and update information of size O(r log(n/r)) where r is the number of revoked users. In this paper, we present a new revocable IBE system in which the private key only contains two group elements and the update information size is O(r). We show that the proposed constructions for the revocation mechanism are more efficient in terms of space cost and provide a generic methodology to transform a non-monotonic attribute based encryption into a revocable IBE. We also demonstrate how the proposed method can be employed to develop an efficient hierarchical revocable IBE system.