Efficient Conditional Proxy Re-encryption with Chosen-Ciphertext Security

In a proxy re-encryption (PRE) scheme a semi-trusted proxy can convert a cipher text under Alice´s public key into a cipher text for Bob. The proxy does not know the secret key of Alice or Bob, and also does not know the plaintext during the conversion. Conditional proxy re-encryption (C-PRE) can implement fine-grained delegation of decryption rights, and thus is more useful in many applications. In this paper, we propose an efficient C-PRE scheme, and prove its chosen-cipher text security under decisional bilinear Diffie-Hellman (DBDH) assumption in the random oracle model. Our scheme has significant advantages in both computational and communicational than previous schemes.