Research profile

Coding Theory

a) Error detecting codes (Check digit systems)(Prüfzeichensysteme) over finite groups; equivalence of check digit systems. See the preprints On check digit systems using anti-symmetric mappings. (PDF) (Preprint A-98-17) and Equivalence of check digit systems over the dicyclic groups....(PDF) (Preprint A-99-10). or the lecture notes on computer science: H.Alt (Ed.): Computational Discrete Mathematics, LNCS 2122, pp. 136-147, 2001: Check character systems and anti-symmetric mappings.(PDF)

b) Constant weight codes which can be constructed from divisible designs and their automorphism groups; see e.g. the preprint Automorphisms of constant weight codes and of divisible designs. (PDF) (Preprint A-97-28, together with A.G.Spera).

Design Theory

Together with A. G. Spera, University of Palermo, and others we study divisible designs, which can be constructed by a permutation group respecting an equivalence relation and operating transitively on the pairs of non-equivalent elements. Preprints are e.g. Construction of divisible designs from translation planes. (Preprint A-97-08, together with A.G.Spera), Divisible designs admitting, as an automorphism group, an orthogonal group or a unitary group. (Preprint A-99-13, together with C.Cerroni) Some Constructions of Divisible Designs from Laguerre Geometries. (Preprint A11/2002. Together with S.Giese and H.Havlicek).
A characterization of divisible designs with elementary abelian dual translation group is given in Divisible Designs with Dual Translation Group.(PDF) ( together with S.Giese; the original publication is available at www.springerlink.com).

Selected older publications:

Über Blockpläne mit transitiver Dilatationsgruppe. Math.Zeitschr.98 (1967) 60-82.
On the lines of special block designs. Journ. Comb.Th. A 14 (1973) 102-112.
Zur Geometrie der $PSU(3,q^{2})$ : Eine Klasse von Steinerschen Systemen. Geom. Dedicata 3 (1974) 11-19.
Zur Geometrie der $PSU(3,q^{2})$. In: Arnold, Benz, Wefelscheid (Hrsg.) Beiträge zur Geometrischen Algebra, Basel, Stuttgart 1977, p.293-298.
Transversal designs and partitions associated with Frobenius groups. Journ.f.d.Reine u.Angew. Math.355 (1985) 153-162.
On the classification of translation group-divisible designs. Europ.J.Comb.6 (1985) 369-374.

Didactics of Coding Theory and of Cryptology

The last in-service training of teachers was in March, 14, 2006

Parts of the material can be found in the following papers.
H.Witten, I.Letzner und R.-H.Schulz: RSA & Co. in der Schule. Moderne Kryptologie, alte Mathematik, raffinierte Protokolle.

• Teil 1: Sprache und Statistik. LogIn 18 Heft 3/4 (1998) S.57-65.
• Teil 2: Von Cäsar über Vigenère zu Friedman. LogIn 18 Heft 5 (1998) 31-39.
• Teil 3: Flusschiffren, perfekte Sicherheit und Zufall per Computer.LogIn 19 Heft 2 (1999) 50-57.

H.Witten und R.-H.Schulz: RSA&Co in der Schule. Moderne Kryptologie, alte Mathematik, raffinierte Protokolle.

• Neue Folge Teil 1: RSA für Einsteiger. LogIn Heft Nr.140 (2006) 45-54.
• Neue Folge Teil 2: RSA für große Zahlen. LogIn Heft 143 (2006) 50-58
• Neue Folge Teil 3: RSA und die elementare Zahlentheorie LogIn Nr.152, p.60-70. 2008. (PDF-Datei)
  

Public Key Cryptography (Part II) (for teachers) (in German)