This volume contains the refereed papers presented at the International Workshop on Software Encryption Algorithms, held at Cambridge University in December 1993. The contributors provide a state-of-the-art report on all theoretical aspects of encryption algorithms, taking into account new demands from new applications. The papers have been organized into sections on block cyphers, stream cyphers, software performance, cryptanalysis, hash functions and hybrid cyphers, and randomness and nonlinearity.