Differential cryptanalysis is a type of attack that can be mounted on iterative block ciphers. These techniques were first introduced by Murphy [Mur90] in an attack on FEAL-4, but they were later improved and perfected by Biham and Shamir who used them to attack DES. Differential cryptanalysis is basically a chosen plaintext attack and relies on an analysis of the evolution of the differences between two related plaintexts as they are encrypted under the same key. By careful analysis of the available data, probabilities can be assigned to each of the possible keys and eventually the most probable key is identified as the correct one.