Improved Hierarchical Identity-Based Parallel Key-Insulated Encryption

Abstract

The problem of key-exposure is an important issue in modern society due to the growing use of mobile devices. Weng et al. proposed an identity-based parallel keyinsulated encryption (IBPKIE) scheme to solve the keyexposure problem in an identity-based cryptosystem. The scheme has long public parameters and a loose security reduction. Ren et al. presented a new IBPKIE scheme which had constant size public parameters and a tight reduction, and then extended it to a hierarchical IBPKIE (HIBPKIE) scheme. However, Wang et al. analyzed two schemes of Ren et al. and showed that they are not secure against chosen-plaintext attack. In this paper, we propose an improved IBPKIE scheme which achieves IND-ID-KI-CPA security without random oracles. Moreover, our scheme has short public parameters and a tight reduction. We then present an HIBPKIE scheme which achieves IND-sID-KI-CPA security without random oracles. In this scheme, the ciphertext size is independent of the level of the hierarchy in the HIBPKIE scheme.