Publication Details

Lawrence Brown and Jennifer Seberry, Key scheduling DES type cryptosystems, (Josef Pieprzyk and Jennifer Seberry, (Eds.)), Auscrypt'90 – Advances in Cryptography, 453, Lecture Notes in Computer Science, Springer-Verlag, (1990), 221-228.


This paper reviews some possible design criteria for the key schedule in a DES style cryptosystem. The key schedule involves a Key Rotation component. and the permutation PC2. Together these provide for a diffusion of dependency of ciphertext bits on key bits. Some empirical rules which seem to account for the derivation of the key schedule used in the DES are first presented. A number of trials were run with various key schedules. and some further design rules were derived. An alternative form of key schedule was then tested. This used either a null PC2, or one in which permutations only occurred within the inputs to a given S-box, and a much larger rotation schedule than used in the DES. This was found to be as effective as the key schedule used in the current DES, and is proposed for use in new cryptosystems.