There have been no significant cryptanalytic attacks on DES other than exhaustive key search. the 8 bits output, but simple DES algorithm, which generates the 4-bits as an output from 6-bits. These keys shall be avoided.ĭES has proved to be a very well designed block cipher. Algorithm Using Extended Substitution Box (S-Box) is to.
These two properties make cipher very strong.Īvalanche effect − A small change in plaintext results in the very great change in the ciphertext.Ĭompleteness − Each bit of ciphertext depends on many bits of plaintext.ĭuring the last few years, cryptanalysis have found some weaknesses in DES when key selected are weak keys. The DES satisfies both the desired properties of block cipher. The logic for Parity drop, shifting, and Compression P-box is given in the DES description. The process of key generation is depicted in the following illustration −
8 BIT S BOX OUTPUT GENERATOR
The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key.
8 BIT S BOX OUTPUT 32 BIT
Straight Permutation − The 32 bit output of S-boxes is then subjected to the straight permutation with rule shown in the following illustration: The output of all eight s-boxes is then combined in to 32 bit section. DES uses 8 S-boxes, each with a 6-bit input and a 4-bit output. − The S-boxes carry out the real mixing (confusion). The round key is used only in this operation. − After the expansion permutation, DES does XOR operation on the expanded right section and the round key. The graphically depicted permutation logic is generally described as table in DES specification illustrated as shown − Permutation logic is graphically depicted in the following illustration − The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output.Įxpansion Permutation Box − Since right input is 32-bit and round key is a 48-bit, we first need to expand right input to 48 bits. The heart of this cipher is the DES function, f.
The initial and final permutations are shown as follows − Round Function They have no cryptography significance in DES.
The initial and final permutations are straight Permutation boxes (P-boxes) that are inverses of each other.