An efficient revocable ID-based encryption scheme in the standard model

Abstract

Similar to the traditional public key setting based on public key infrastructure, in the application of identity-based cryptosystems, it is also important to provide a practical mechanism for revoking those users whose private keys are compromised or they are no longer legitimate system users. This paper concentrates on the practical user revocation problem in identity-based encryption (IBE) systems. We present an efficient and CCA2 secure revocable identity-based encryption (RIBE) scheme in the standard model. The revocation mechanism put forward in our RIBE scheme does not require secure channels between the PKG and the users. The CCA2 security of our scheme is rigorously proved and is tightly reduced to the hardness assumption of the decisional truncated q-ABDHE problem without using random oracles. Additionally, our RIBE scheme also supplies a mechanism that permits the revoked users to rejoin the system without altering their identity information or rebuilding the system.