In [8], a characterization of the finite quadric Veronesean V 2 n n by means of properties of the set of its tangent spaces is proved. These tangent spaces form a regular generalised dual arc. We prove an extension result for regular generalised dual arcs. To motivate our research, we show how they are used to construct a large class of secret sharing schemes.A typical problem in (finite) geometry is the study of highly symmetrical substructures. For example, arcs are configurations of points in PG(n, q) such that each n + 1 of them are in general position, while n 1 -dimensional dual arcs are sets of n 1 -spaces such that each two intersect in a point and any three of them are skew. These two structures appear naturally in cryptographical applications.In this article, we define objects, called (generalised) dual arcs; a class of objects that contain classical arcs and n 1 -dimensional dual arcs as special cases. These (generalised) dual arcs have applications in cryptography as well.We give a construction method for a wide class of parameters and prove an extension result for regular generalised dual arcs of order d = 1.In Sections 1 and 2, we give the necessary definitions, constructions, and examples of applications in cryptography. Section 3 refers to known classification results, and Section 4 states our main characterization theorem (Theorem 13). We now start with the required definitions to make this article self-contained.