An Escrow-Free Hierarchical Identity-Based Signature Scheme from Composite Order Bilinear Groups

Hierarchical Identity-Based Signature (HIBS) is an efficient digital signature scheme to be applied to the cloud storage. However, the key escrow problem, which is an inherent problem in HIBS scheme, primarily hinders the widespread adoption of this cryptosystem in practice. In this paper we propose an HIBS scheme using composite order bilinear groups, and present the methodology of dual system signature to prove that our scheme is secure against existential forgery on adaptively chosen message and identity attack under standard model. Based on the scheme, we propose an escrow-free method that employs user-selected-secret signing algorithm and obtain an escrow-free HIBS scheme. We illuminate that our scheme can resist the key abusing and user slandering attacks.