Digraph-defined external difference families and new circular external difference families

Abstract: External difference families (EDFs) are combinatorial objects which were introduced in the early 2000s, motivated by information security applications; various generalizations have since been defined and investigated, in particular strong EDFs (SEDFs) and circular EDFs (CEDFs). We present a framework based on graphs and digraphs which offers a new unified way to view these structures, and leads to natural new research questions. We present constructions and structural results about these digraph-defined EDFs, and we obtain new explicit constructions for infinite families of CEDFs, in particular $(ml<sup>2,m,l,1)$-CEDFs. We construct the first infinite family of such CEDFs in non-cyclic abelian groups; these have odd values of $m$ and $l$. We also present the first CEDF in a non-abelian group.