New escrow-free scheme for hierarchical identity-based encryption

Abstract

Key escrow is an inherent problem in identity-based encryption (IBE) since it was first proposed by Shamir in 1984. We present a new scheme to remove key escrow from IBE and HIBE, based on the security notion of anonymous ciphertext indistinguishability against key generation center (ACI-KGC) proposed by Chow. In view of this, we first show how to equip a modified framework in (H)IBE system in ACI-KGC security. In the system architecture, the PKG and ICA cooperate an anonymous private key generation protocol such that the PKG can issue a private key to a user authenticated by ICA without knowing the list of users’ identities. Next, we apply proposed scheme to hierarchical identity-based encryption (HIBE) system to ensure the high security and efficiency. It is worth noting that, our proposal focus on the mitigating the key escrow problem which has not been well-studied in HIBE, and do not change the fundamental structure of systems as well as keep the efficiency and security of HIBE.