Data Encryption Standard (DES) and Advanced Encryption Standard (AES)

Definition

Data Encryption Standard (DES) and Advanced Encryption Standard (AES) are designed to encrypt a sequence of data elements.

The DES algorithm is designed to encipher and decipher 64-bit blocks of data under control of a 64-bit key, of which 56 bits are randomly generated and used directly by the algorithm. Deciphering must be accomplished by using the same key as for enciphering. The deciphering process is the reverse of the enciphering process. A 64-bit block to be enciphered is subject to an initial permutation to form L ₀ and R ₀ (32 bits each, respectively the left and right half of the 64-bit block generated by the initial permutation), then to 16-iteration key-dependent computation, and the final result of the computation (L ₁₆ and R ₁₆) is subject to a permutation that is the inverse of the initial permutation. The 16 key-dependent computations can be simply defined as [1]:

$$\begin{array}{*{20}l}L_n &= R_{n - 1} \\ R_n &= L_{n - 1} \oplus f(R_{n - 1} ,K_n...