Fast Software Encryption (FSE) is an annual research workshop devoted to the promotion of research on classical encryption algorithms and related cryp- graphic primitives such as hash functions. When public key cryptography started to receive wide attention in the 1980s, the much older and more basic art of secret key cryptography was sidelined at many research conferences. This motivated Ross Anderson to organise the rst FSE in Cambridge, England in December 1993; subsequent workshops followed at Leuven, Belgium (December 1994), Cambridge again (February 1996), and Haifa, Israel (January 1997). These proceedings contain the papers due to be presented at the fth FSE workshop in March 1998 at the Hotel du Louvre in Paris. This event is organized by the Ecole Normale Superieure and the Centre National pour la Recherche S- enti que (CNRS) in cooperation with the International Association for Cryp- logic Research (IACR), and has attracted the kind support of Gemplus and Microsoft, the world leaders in smart cards and software { two domains very closely connected to our research concerns.