Identity-based conditional proxy re-encryption without random oracles

In an identity-based proxy re-encryption (IB-PRE) scheme, a semi-trusted proxy can convert a ciphertext under Alice´s identity into a ciphertext for Bob. The proxy does not know the secret key of Alice or Bob, and also does not know the plaintext during the conversion. However, some scenarios require handle a fine-grained delegation. In this paper, by using the identity-based encryption (IBE) technique of Boneh-Boyen, we propose a new identity-based conditional proxy re-encryption (IBCPRE) scheme, which enables Alice to implement finegrained delegation of decryption rights, and thus is more useful in many applications. Our scheme has significant advantages in both computational and communicational than Shao et al.´s IBCPRE scheme.