Differential–Linear Attack

Related Concepts

Block Ciphers; Data Encryption Standard (DES)

Definition

Differential–Linear attack is a chosen plaintext two-stage technique of cryptanalysis (by analogy with two-stage rocket technology) in which the first stage is covered by differential cryptanalysis, which ensures propagation of useful properties midway through the block cipher. The second stage is then performed from the middle of the cipher and to the ciphertext using linear cryptanalysis. The technique was discovered and demonstrated on the example of 8-round DES (Data Encryption Standard) by Langford and Hellman [ 4].

Theory

Given a differential characteristic with probability p for the rounds $1,\ldots ,i$ and the linear characteristic with bias q for the rounds $i + 1,\ldots ,\ R$, the bias of resulting linear approximation would be $1/2 + 2{\mathit{pq}}^{2}$ and the data complexity of the attack will be $O({p}^{-2}{q}^{-4})$ [3, p. 65]. Thus the attack would be useful only in special cases when...