this paper we will describe DES and briefly present TDEA. Furthermore, we will describe an attack (differential cryptanalysis) that can be applied not only to DES but to many DESlike iterated cryptosystems (such as Lucifer, FEAL  and GDES ). This is a chosen plaintext attack which uses only the resultant ciphertexts. The basic tool of the attack is the ciphertext pair: a pair of ciphertexts whose plaintexts have particular differences (thus the name differential). The two plaintexts can be chosen at random, as long as they satisfy the difference condition, and the cryptanalyst does not have to know their values. The attack is statistical in nature and can fail in rare instances.