New Constructions for Identity-Based Unidirectional Proxy Re-Encryption

We address the cryptographic topic of proxy re-encryption (PRE), which is a special public-key cryptosystem. A PRE scheme allows a special entity, known as the proxy, to transform a message encrypted with the public key of a delegator (say Alice), into a new ciphertext that is protected under the public key of a delegatee (say Bob), and thus the same message can then be recovered with Bob's private key. In this paper, in the identity-based setting, we first investigate the relationship between so called mediated encryption and unidirectional PRE. We provide a general framework which converts any secure identity-based unidirectional PRE scheme into a secure identity-based mediated encryption scheme, and vice versa. Concerning the security for unidirectional PRE schemes, Ateniese et al. previously suggested an important property known as the master secret security, which requires that the coalition of the proxy and Bob cannot expose Alice's private key. In this paper, we extend the notion to the identity-based setting, and present an identity-based unidirectional PRE scheme, which not only is provably secure against the chosen ciphertext attack in the standard model but also achieves the master secret security at the same time.