Improved online/offline attribute based encryption and more

Abstract

Attribute based encryption is a very useful primitive for scalable access control on the ciphertexts and has found broad applications, such as secure cloud storage etc. When this primitive is used by mobile phones, the computation cost is too heavy. So Hohenberger and Waters introduced the concept of Online/offline attribute based encryption and give a such concrete construction. In this paper, we give an improved construction based on their proposal. Compared with their proposal, our proposal needs 5 pairings instead of 2|I|+1 pairings, which is much more efficient than the original scheme. Furthermore, we generalize this technique to speed up the computation of multi-modular exponentiation, and thus also get an interesting result.