Sender dynamic, non-repudiable, privacy-preserving and strong secure group communication protocol

Establishing a secure communication channel among a group of individuals is a critical issue in group oriented applications. In implementation, besides the basic confidentiality requirement, we also expect the group communications to be sender dynamic, forward secure, non-repudiable and privacy preserving. Traditional approaches, i.e., group key agreement and broadcast encryption cannot achieve the above requirements simultaneously and efficiently. In this paper, we propose our solution to secure group communications using a new security tool called identity based asymmetric group key agreement protocol with sender non-reputation and privacy. The new notion allows a group of users to negotiate a common group encryption key and their respective group decryption keys. After that, users inside/outside the group who have the knowledge of the group encryption key are able to send non-repudiable and privacy-preserving messages to the group confidentially. Further, even all the users' private keys are later corrupted, the messages broadcasted previously remain secure. Following this definition, we propose a concrete protocol which is proven to be secure against chosen-ciphertext attacks (CCA) directly. We also show the potential applications of our new protocol in instant messaging applications, such as Whatsapp, Wechat, Messenger.