The volume contains the papers presented at the fifth working conference on Communications and Multimedia Security (CMS 2001), held on May 21-22, 2001 at (and organized by) the GMD -German National Research Center for Information Technology GMD - Integrated Publication and Information Systems Institute IPSI, in Darmstadt, Germany. The conference is arranged jointly by the Technical Committees 11 and 6 of the International Federation of Information Processing (IFIP) The name "Communications and Multimedia Security" was first used in 1995, Reinhard Posch organized the first in this series of conferences in Graz, Austria, following up on the previously national (Austrian) "IT Sicherheit" conferences held in Klagenfurt (1993) and Vienna (1994). In 1996, the CMS took place in Essen, Germany; in 1997 the conference moved to Athens, Greece. The CMS 1999 was held in Leuven, Belgium. This conference provides a forum for presentations and discussions on issues which combine innovative research work with a highly promising application potential in the area of security for communication and multimedia security. State-of-the-art issues as well as practical experiences and new trends in the areas were topics of interest again, as it has already been the case at previous conferences. This year, the organizers wanted to focus the attention on watermarking and copyright protection for e­ commerce applications and multimedia data. We also encompass excellent work on recent advances in cryptography and their applications. In recent years, digital media data have enormously gained in importance.