Preface: geometry, combinatorial designs and cryptology

This issue of the journal is devoted to the themes of Geometry, Combinatorial Designs and Cryptology. The guest editors selected sixteen contributions covering various areas within these themes, ranging from public-key cryptography to matters related to key distribution and authentication, from problems in graph theory to resolvability issues in designs, from finite projective planes to higher-dimensional geometries.Many problems in these areas share commonmethods, including purely combinatorial techniques, but also algebraic methods for finite fields, geometric issues mainly involving incidence and collineations, and computational approaches. The papers “Projective k-arcs and 2-level secret-sharing schemes” by Korchmáros– Lanzone–Sonnino (doi:10.1007/s10623-011-9562-5), “Singer 8-arcs of Mathon type in PG(2, 27)” by De Clerck–De Winter–Maes (doi:10.1007/s10623-011-9502-4) and “42arcs in PG(2, q) left invariant by P SL(2, 7)” by Indaco–Korchmáros (doi:10.1007/ s10623-011-9532-y) deal with arcs and address questions related to their construction, maximality and classification up to projective equivalence. Polar spaces are the subject of the papers “Two forms related to the symplectic dual polar space in odd characteristic” by Cardinali–Pasini (doi:10.1007/s10623-011-9545-6) and “Collineations of polar spaces with restricted displacements” by Temmermans–Thas– Van Maldeghem (doi:10.1007/s10623-011-9509-x). In particular the description of these spaces in terms of forms and properties of their collineations are considered.