DES is not a Group

We prove that the set of DES permutations (encryption and decryption for each DES key) is not closed under functional composition. This implies that, in general, multiple DES-encryption is not equivalent to single DES-encryption, and that DES is not susceptible to a particular known-plaintext attack which requires, on average, 228 steps. We also show that the size of the subgroup generated by the set of DES permutations is greater than 102499 , which is too large for potential attacks on DES which would exploit a small subgroup.

• Type: Conference
• Year: 1992
• Where: CRYPTO
• Authors: Keith W. Campbell, Michael J. Wiener
• Keywords: CRYPTO 1992, Cryptology, DES Permutations, Functional Composition, Particular Known-plaintext Attack