DES-X (or DESX)

Related Concepts

Block Ciphers; Feistel Cipher; Slide Attack

Definition

DES-X is a 64-bit block cipher with a $2 \times 64 + 56 = 184$-bit key, which is a simple extension of DES (Data Encryption Standard).

Background

The construction was suggested by Rivest in 1984 in order to overcome the problem of the short 56-bit key-size which made the cipher vulnerable to exhaustive key search attack. The idea is just to XOR a secret 64-bit key K1 to the input of DES and to XOR another 64-bit secret key K2 to the output of DES: $C = K2 \oplus {\mathit{DES}}_{K}(P \oplus K1)$. The keys K1, K2 are called whitening keys and they became a popular element of modern cipher design. The construction itself goes back to the work of Shannon [6, p. 713], who suggested the use of a fixed mixing permutation whose input and output are masked by the secret keys. This construction has been shown to have provable security by Even–Mansour [2] if the underlying permutation is pseudorandom(i.e.,...