An Improved Unbounded HIBE Scheme in the Prime Order Setting.

Unbounded Hierarchical Identity-Based Encryption (HIBE) is a new HIBE where the public parameters size is constant and independent of the length of the identity vectors. In this paper, we improve Lewko-Waters unbounded HIBE scheme and get a new give an HIBE scheme. Our scheme is constructed in the prime order setting, and more efficient than previous unbounded HIBE schemes. Furthermore, our scheme removes the constraint on hierarchical identity in the LewkoWaters construction and can be proven selective security in the security model.