This book constitutes the thoroughly refereed post-proceedings of the 9th International Workshop on Fast Software Encryption, FSE 2002, held in Leuven, Belgium in February 2002. The 21 revised full papers presented were carefully reviewed and selected from 70 submissions. The papers are organized in topical sections on blook cipher cryptoanalysis, integral cryptoanalysis, block cipher theory, stream cipher design, stream cipher cryptanalysis, and odds and ends.