Verifiable and Anonymous Encryption in Asymmetric Bilinear Maps

Consider a practical scenario: an untrusted gate-way is required to verify all the incoming information en-crypted via an encryption scheme, while the sender does not want to reveal any information about the plaintext and the privileged user to the gateway. That is, the gateway distributes the information to a predefined group of users and only the privileged user can open the message. To solve this problem, we need an access control mechanism to allow certain specification of the access control policies while protecting the users´ privacy. With this scenario in mind, we propose the notion of verifiable and anonymous encryption where a verification function is added to the ciphertext, which captures the security requirements of the confidentiality of the plaintext and the anonymity of the privileged user. We present two specific constructions of our framework under the setting of asymmetric bilinear pairings in this paper. Our first scheme is proven confidential and anonymous under a weaker security model in the random oracle model, and our second one is built on the basis of a zero knowledge proof of knowledge under a strong security game.