Removing key escrow from the LW-HIBE scheme

Abstract

Hierarchical Identity-Based Encryption (HIBE) provides an efficient solution to the security problems existed in cloud storage. However, the key escrow problem, which is an inherent problem in HIBE, primarily hinders the widespread adoption of the cryptographic scheme in practice. To address the key escrow problem, this paper introduces a provably-secure escrow-free model, which employs multiple Key Privacy Authorities (KPAs) to restrict the power of Public Key Generators (PKGs) in HIBE scheme. We instantiate the model into an escrow-free HIBE scheme that is referred to as the EF-LW-HIBE scheme, based on the HIBE scheme introduced by Lewko and Waters. Utilizing the Dual System Encryption methodology, we prove that our EF-LW-HIBE scheme is IND-ID-CCA secure.