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. Any additional processing − Initial and final permutation.Since DES is based on the Feistel Cipher, all that is required to specify DES is − General Structure of DES is depicted in the following illustration − Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm (function as check bits only). ![]() The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST).ĭES is an implementation of a Feistel Cipher.
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