  We study the problem of secure message multicasting over graphs in the
presence of a passive (node) adversary who tries to eavesdrop in the network.
We show that use of feedback, facilitated through the existence of cycles or
undirected edges, enables higher rates than possible in directed acyclic graphs
of the same mincut. We demonstrate this using code constructions for canonical
combination networks (CCNs). We also provide general outer bounds as well as
schemes for node adversaries over CCNs.
