— Both broadcast encryption (BE) protocols and multicast key distribution (MKD) protocols try to solve the same problem of private group communication. For the first time, we discuss fundamental differences between BE protocols and MKD protocols from multiple perspectives, and reveal subtle connections between them. Both efficient BE protocols and MKD protocols are usually based on some types of access control structures. Compared with the static access control structures employed by BE protocols, those employed by MKD protocols need be updated upon every single change in group membership, and thus are highly dynamic. It has been shown that instantiation of a dynamic access control structure that’s based on one-way function (OWF) by using homomorphic one-way function (HOWF) helps improve the efficiency of these update operations. In this paper, we introduce two new HOWF-based access control structures — Bi-Directional Homomorphic One-way Function Chain (BD-HOFC) and Top-down Homo...