@unpublished{Guthmann1999,
  author  = {Andreas Guthmann},
  title   = {Vigenere-Verschl{\"u}sselung},
  institution = {Fachbereich Mathematik},
  series    = {Preprints (rote Reihe) des Fachbereich Mathematik},
  number    = {312},
  year    = {1999},
  url  = {http://nbn-resolving.de/urn:nbn:de:hbz:386-kluedo-7602},
}