## DES (Data Encryption Standard) Basic Description

DES (Data Encryption Standard) represents the Federal Information Processing Standard (FIPS) 46-3 describing the data encryption algorithm (DEA). The DEA is also defined in the ANSI standard X3.92. It uses 16 round Feistel structure and the block size is 64-bit. Data encryption algorithm represents an improvement of the Lucifer algorithm that was developed in the early 1970s by IBM.

During the last few years, cryptanalysis have found some weaknesses in DES when key selected are weak keys. Data Encryption Standard was replaced by Triple DES which has itself been superseded by AES. During communication via Data Encryption Standard, both sender and receiver must know the same secret key. It can be used to encrypt and decrypt the message, or to generate and verify MAC (Message Authentication Code).

Data Encryption Standard key length is 64-bit, however, it has an effective key length of 56 bits. 8 of the 64 bits of the key are not used by the encryption algorithm. These sizes are too small by today’s standards. Data Encryption Standard is an implementation of a Feistel Cipher.

General Structure of Data Encryption Standard is depicted in the following illustration –

**Data Encryption Standard Modes of Operation**

- ECB (Electronic Code Book)
- CBC (Cipher Block Chaining)
- CFB (Cipher Feedback)
- OFB (Output Feedback)

**Data Encryption Standard Analysis**

The DES satisfies both the desired properties of block cipher that make cipher very strong.

- Avalanche effect − A small change in plaintext results in the very great change in the ciphertext.
- Completeness − Each bit of ciphertext depends on many bits of plaintext.