output feedback (DES) (OFB)
Output feedback (OFB) is a mode of operation of block cipher algorithms, such as the Data Encryption Standard( DES), which, like key feedback( CFB), is an XOR operation of two text blocks followed by ciphering.
In this block cipher, it is not the key text variables but the output variables of the encryption operation itself that are fed back as input for the next encryption operation. The complete output block is used as the next input block. In OFB mode, the same plaintext results in the same keytext if the same key and the same initialization vector( IV) are used. To prevent this from happening, either always start with a different plaintext or use a different initialization vector or key.
In OFB operation, there is no chaining, which makes the method more vulnerable to attack. Similar to Output Feedback, Counter Mode( CTR) works by converting block cipher to stream cipher.
Unlike Cipher Feedback (CFB), OFB has another XOR operation of the ciphered text with a pseudo stream.