Data Encryption Standard (DES): Initial permutation + Round function + XOR and Swap

After initial permutation, we had two 32-bit plain text areas called as Left Plain Text (LPT) and Right Plain Text (RPT). During the expansion permutation: The RPT is expanded from 32 bits to 48 bits. Bits are permuted as well, hence called as Expansion Permutation. Expansion the 32 bit RPT is divided into 8 blocks, with each block consisting of 4 bits. Then, each 4 bit block of the previous step is then expanded to a corresponding 6 bit block (2 more bits are added). Now the 48-bit key is XOR with 48-bit RPT and resulting output is given to the next step, which is the S-Box substitution.