Don Coppersmith: The Data Encryption Standard (DES) and its strength against attacks. In: International Business Machines Corporation (Hrsg.): IBM Journal of Research and Development. Band38, Nr.3, 3. Mai 1994, S.247, Absch. Design Criteria Nr. S-4 (simson.net [PDF]): „If two inputs to an S-box differ in exactly one bit, the outputs must differ in at least two bits.“
