Which mode of DES functions by means of taking each block of

Which mode of DES functions by means of taking each block of cipher text and XORing it with the next plain text block to be encrypted with the result of a dependency on all the previous blocks?

A. ECB

B. CBC

C. CFB

D. OFB

Solution

B. Cipher Block Chaining (CBC) builds a dependency between the blocks of data. To find the plain text of a particular block, you need to know the cipher text, the key, and the cipher text for the previous block. This feature makes CBC unique. Answer A is incorrect because Electronic Code Book is fast but not chained or secure. Answer C is incorrect because Cipher Feedback (CFB) can be used to emulate a stream cipher and features a feedback function. Answer D is incorrect because Output Feedback (OFB) can also emulate a stream cipher and can pregenerate the key stream independent of the data.