Data Encryption Standard (DES)

INTRODUCTION

The Data Encryption Standard (DES) is a symmetric block cipher which takes the input of 64-bit plain text along with 64-bit key and process it, to generate the 64-bit ciphertext. DES was published by the National Institute of Standards and Technology (NIST).The data encryption standard is a common standard for data encryption and a form of secret key cryptography (SKC), which uses only one key for encryption and decryption.

In 1973, NIST published a request for proposals for a national symmetric-key cryptosystem. A proposal from IBM, a modification of a project called Lucifer, was accepted as DES. DES was published in the Federal Register in March 1975 as a draft of the Federal Information Processing Standard (FIPS).

WHAT IS DES?

►DES Use Symmetric system means both sender and receiver side we used same key for encryption and decryption.

►DES used 64 bits of block for encryption and decryption.

►Sixteen rounds of transposition and substitution are performed in order to achieve DES.

HOW DOES DES WORK ?

• DES is a symmetric block encryption algorithm.When 64-bit blocks of plaintext go in, 64-bit blocks of cipher text come out.

• It is also a symmetric algorithm, meaning the same key is used for encryption and decryption.

• It uses a 64-bit key: 56 bits make up the true key, and 8 bits are used for parity.

• When the DES algorithm is applied to data, it divides the message into blocks and operates on them one at a time.

• The blocks are put through 16 rounds of transposition and substitution functions.The result is 64-bit blocks of ciphertext.

DES MODES

• Block ciphers have several modes of operation. Each mode specifies how a block cipher will operate.

• Electronic Code Book (ECB)

• Cipher Block Chaining (CBC)

• Cipher Feedback (CFB)

• Output Feedback (OFB)

• Counter Mode (CTR)

ELECTRONIC CODE BOOK MODE

• It Inherit core functionality from their parent block which is Symmetric System.

• Like 64 bits of block use for encryption and decryption.

• Use Same key for encryption and decryption of all blocks of data.

CIPHER BLOCK CHAINING MODE

• Cipher Block Chaining (CBC) does not reveal a pattern, because each block of text, the key, and the value based on the previous blocks.

• This results in more random ciphertext.

• This provides dependence between the blocks, in a sense chaining them together.

CIPHER FEEDBACK MODE (CFB)

• The CBC mode is great to use when you need to send large chunks of data at a time but when the need of send small amount of data at a time we use CFB.

• Cipher Feedback is the combination of block cipher and stream cipher.

OUTPUT FEEDBACK MODE

• It Cover the weakness of Cipher feedback mode.

• Almost Same process of encryption and decryption.

COUNTER MODE (CTR)

• There is no chaining involved in Counter Mode (CTR) like other three types.

I. Cipher block Chaining.

II. Cipher Feedback.

III. Output Feeback.

• Each block is individually decrypted without depending on other blocks.

• the encryption of the individual blocks can happen in parallel, which increases the

performance.