Group key agreement protocols are crucial for achieving secure group communications.They are designed to provide a set of users with a shared secret key to achieve cryptographic goal over a public network.When group membership changes,the session key should be refreshed efficiently and securely.Most previous group key agreement protocols need at least two rounds to establish or refresh session keys.In this paper,a dynamic authenticated group key agreement(DAGKA) protocol based on identity-based cryptography is presented.By making use of the members’ values stored in previous sessions,our Join and Leave algorithms reduce the computation and communication costs of members.In the proposed protocol,Setup and Join algorithms need one round.The session key can be refreshed without message exchange among remaining users in Leave algorithm,which makes the protocol more practical.Its security is proved under decisional bilinear Diffie-Hellman(DBDH) assumption in random oracle model. Group key agreement protocols are crucial for achieving secure group communications. They are designed to provide a set of users with a shared secret key to achieve cryptographic goal over a public network. Organization group membership changes, the session key should be refreshed efficiently and securely. Most previous group key agreement protocols need at least two rounds to establish or refresh session keys. In this paper, a dynamic authenticated group key agreement (DAGKA) protocol based on identity-based cryptography is presented. By making use of the members’ values ​​stored in previous sessions, our Join and Leave algorithms reduce the computation and communication costs of members. The proposed protocol, Setup and Join algorithms need one round. The session key can be refreshed without message exchange among remaining users in Leave algorithm, which makes the protocol more practical.Its security isarently under decisional bilinear Diffie-Hellman (DBDH) assumption in random oracle model.