PRE: Stronger security notions and efficient construction with non-interactive opening

In a proxy re-encryption (PRE) scheme, a proxy is given a re-encryption key and has the ability to translate a ciphertext under one key into a ciphertext of the same message under a different key, without learning anything about the message encrypted under either key. This paper first shows that the chosen key (CK) model which allows the adversary to adaptively choose public keys for malicious users, is strictly stronger than the knowledge of secret key models (KOSK) that most of previous PREs rely on. Then, the paper presents an efficient CCA secure PRE scheme in the stronger CK model based on the decisional bilinear Diffie-Hellman (DBDH) assumption without the random oracle heuristic. The paper also considers a useful property in PRE applications, namely, “non-interactive opening” and an extended scheme is given to support the property. Compared with previous schemes, the PRE scheme in this paper has a good overall performance in terms of ciphertext length, computational cost, strong and realistic security model as well as a well-studied assumption.