Identity-Based Encryption

Rui Zhang, Yang Tao

Zhongmei Wan, Jian Weng, Xuejia Lai +2 more

Identity-based proxy re-encryption (IBPRE) is a useful primitive, in the sense that a semi-trust proxy can translate ciphertexts originally intended for one identity into ciphertexts intended for another identity. The proxy, however, cannot learn anything about the underlying plaintexts. Mediated identity-based encryption (MIBE), introduced by Ding et al., is particularly useful for the immediate revocation of identities. In this paper, we study the relation between IBPRE and MIBE. We show that, under the chosenplaintext attack (CPA), IBPRE and MIBE are equivalent: we give a generic construction of CPA-secure IBPRE scheme from any CPA-secure MIBE scheme; and a generic construction for the opposite direction is also given. However, under the chosen-ciphertext attack (CCA), we show that IBPRE and MIBE are not equivalent: for an IBPRE scheme generically constructed from CCA-secure MIBE, we can give a concrete attack against this resulting IBPRE scheme; similarly, we also give a concrete attack against the MIBE scheme generically constructed from CCA-secure IBPRE. We believe that our results are theoretically interesting, since for the first time they clarify the relation between IBPRE and MIBE.

Dennis Hofheinz, Christian Matt, Ueli M. Maurer

Shi-Yu Shen, Hongbing Wang, Yunlei Zhao

Yang Lu, Jiguo Li

In this paper, we propose a generic construction of forward-secure identity-based encryption. We first introduce a relaxed variant of hierarchical identity-based encryption called identity-based binary tree encryption and construct a concrete identity-based binary tree encryption scheme which is provably secure in the standard model. We then show that forward-secure identity-based encryption can be generically constructed from identity-based binary tree encryption. Based on the proposed identity-based binary tree encryption scheme, we obtain a direct chosen-ciphertext secure forward-secure identity-based encryption scheme without random oracles.

Yang Lu, Jiguo Li

The primitive of forward-secure identity-based encryption was proposed in order to minimize the damage of private key exposure in identity-based encryption setting. This new primitive guarantees that even if the current private keys are compromised, it is not possible to compromise past secret keys and past communications. In this paper, we propose a generic construction of forward-secure identity-based encryption. To do so, we first introduce a relaxed variant of hierarchical identity-based encryption called identity-based binary tree encryption and construct a concrete identity-based binary tree encryption scheme that is provably chosen-ciphertext secure in the standard model. We then show how to generically construct forward-secure identity-based encryption from identity-based binary tree encryption. Based on the proposed identity-based binary tree encryption scheme, we obtain a forward-secure identity-based encryption scheme with chosen-ciphertext security in the standard model.