DES(Data Encryption Standard)

• DES algorithm developed at IBM under the leadership of WL Tuchman in 1972. This algorithm is based on the Lucifer algorithm, which is made by Horst Feistel.

• This algorithm has been approved by the National Bureau of Standards (NBS) after its power rating by the National Security Agency (NSA), the United States.

• DES included in symmetric cryptographic systems and classified as the type block ciphers.

• DES operates on 64 bit block size. 64 bit DES encryption to 64 bits of plaintext to ciphertext using a key 56-bit internal (internal key) or upa-key (subkey). Internal key generated from an external key (external key) whose length is 64 bits.

• the global scheme of the DES algorithm is as follows (see Figure 1):
1. Dipermutasi plaintext block with initial permutation matrix (initial permutation or IP).
2. The result of initial permutation and then in-enciphering-16 times (16 rounds). Each round uses a different internal keys.
3. Results enciphering then dipermutasi with permutation matrix inverse (or inverse initial permutation IP-1) into ciphertext blocks.

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Figure 1. Global scheme of the DES algorithm

• In the process of enciphering, plaintext block is divided into two parts, left (L) and right (R), each 32 bits in length. Both parts are entered into the 16 rounds of DES.

• In each round i, block R is an input to the transformation function called f. In function f, R block combined with an internal key Ki. Dai output function f is XOR with a block of the block R L to get a new one. Meanwhile, a new block of L was taken directly from the previous R block. This is one round of DES.

Mathematically, one round of DES is expressed as

Li = Ri - 1
Ri = Li - 1 + f (Ri - 1, Ki)

Figure 2 shows the scheme of the DES algorithm which is more detailed.

Figure 2. DES Algorithm Encryption