The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST). It uses single key (secret key) for both encryption and decryption. It operates on 64-bit blocks of data with 56 bits key. The round key size is 48 bits.
Entire plaintext is divided into blocks of 64bit size; last block is padded if necessary. Multiple permutations and substitutions are used throughout in order to increase the difficulty of performing a cryptanalysis on the cipher. DES algorithm consists of two permutations (P-boxes) and sixteen Feistel rounds. Entire operation can divided into three phase.First phase is Initial permutation and last phase is the final permutations.
1. Initial permutation rearranges the bits of 64-bit plaintext. It is not using any keys, working in a predefined form.
2. There are 16 fiestel rounds in second phase. Each round uses a different 48-bit round keyapplies to the plaintext bits to produce a 64-bit output, generated according to a predefined algorithm. The round-key generator generates sixteen 48-bit keys out of a 56-bit cipher key.
3. Finally last phase perform Final permutation, reverse operation of initial permutation and the output is 64-bit cipher text.