This book constitutes the thoroughly refereed post-workshop proceedings of the 5th Annual International Workshop on Selected Areas in Cryptography, SAC '98, held in Kingston, Ontario, Canada in August 1998. The 26 revised full papers presented together with two invited papers were carefully selected from 39 submissions after two rounds of reviewing and revision. The book is divided in topical sections on designs of secret key cryptosystems, randomness and computational issues, analysis of secret key cryptosystems, cryptographic systems, design and implementation of secret key cryptosystems, and attacks on secret key cryptosystems.