How Data Encryption Standard (DES) operates in four modes

1. Cipher Block Chaining (CBC)
2. Electronic Code Book (ECB)
3. Cipher Feedback (CFB)
4. Output Feedback (OFB)

Cipher Block Chaining
Cipher Block Chaining (CBC) operates with plaintext blocks of 64 bits. A randomly generated 64-bit initialization vector is XORed with the first block of plaintext used to disguise the first part of the message that might be predictable (such as Dear Sir). The result is encrypted by using the DES key. The first ciphertext will then XOR with the next 64-bit plaintext block. This encryption continues until the plaintext is exhausted. Note that in this mode, errors propagate.

Electronic Code Book (ECB)
Electronic Code Book (ECB) is the “native” mode of DES and is a block cipher. ECB is best suited for use with small amounts of data. It is usually applied to encrypt initialization vectors or encrypting keys. ECB is applied to 64-bit blocks of plaintext, and it produces corresponding 64-bit blocks of ciphertext. ECB operates by dividing the 64-bit input vector into two 32-bit blocks called a Right Block and a Left Block. The bits are then recopied to produce two 48-bit blocks. Then, each of these 48-bit blocks is XORed with a 48-bit encryption key. The nomenclature “code book” is derived from the notion of a codebook in manual encryption, which has pairs of plaintext and the corresponding code. For example, the word “RETREAT” in the codebook might have the corresponding code “5374.”

Cipher Feedback (CFB)
The Cipher Feedback (CFB) mode of DES is a stream cipher where the ciphertext is used as feedback into the key generation source to develop the next key stream. The ciphertext generated by performing an XOR of the plaintext with the key stream has the same number of bits as the plaintext. In this mode, errors will propagate.

Output Feedback
The DES Output Feedback (OFB) mode is also a stream cipher that generates the ciphertext key by XORing the plaintext with a key stream. In this mode, errors will not propagate. Feedback is used to generate the key stream; therefore, the key stream varies. An initialization vector is required in OFB