Secure one-to-group communications escrow-free ID-based asymmetric group key agreement

Group key agreement (GKA) is widely employed for secure group communications. Yet there is an increasing demand for secure one-to-group communications in distributed computing applications. Asymmetric group key agreement (AGKA) is a handy tool to answer this need. In AGKA, a group of members can establish a group public key while each member has a different secret key. Any sender can encrypt under this group key such that any of the members who hold the secret key can decrypt. This paper proposes an identity-based AGKA protocol which is secure against active attackers, with an emphasis on optimal round efficiency, sender dynamics, and escrow freeness. The last feature offers security of the previously established ciphertexts even when either all the involved participants or the key generation center of the identitybased cryptosystem are compromised. The proposed protocol is shown to be secure under the k-Bilinear Diffie-Hellman exponent assumption in the random oracle model. Regarding performance, our protocol is comparable to the state-of-the-art AGKA protocols.