Abstract: We study the problem of broadcasting confidential information to a collection of $n$ devices while providing the ability to revoke an arbitrary subset of those devices (and tolerating collusion among the revoked devices). In this paper, we restrict our attention to low-memory devices, that is, devices that can store at most $O(\log n)$ keys. We consider solutions for both zero-state and low-state cases, where such devices are organized in a tree structure $T$. We allow the group controller to encrypt broadcasts to any subtree of $T$, even if the tree is based on an multi-way organizational chart or a severely unbalanced multicast tree. This is joint work with David Eppstein and Jonathan Z. Sun.