How Cipher Feedback Works - Paper Example

Cipher feedback is an operational mode employed by block ciphers. It is similar to cipher block chain mode, and it also uses of the initialization vector (IV). It uses the block cipher as an element for generating random numbers. The cipher-text mode is encrypted, and the output is XOR-ed with the present plaintext block to generate the present text block. It is impossible to directly workout the plaintext unless the recovery of blocks from the start or end of the ciphertext. The XOR operation conceals the plaintext patterns. The resulting entropy is capable of being implemented to a stream cipher. Moreover, cipher feedback is essentially a mode that can be used to derive particular components of a stream cipher specifically from a block cipher. Just like the case with CBC mode, adjusting the IV to a similar plaintext block brings about different output. Despite the fact that the IV does not need to be secret, a couple of other application would consider this desirable. Chaining dependencies present with similarities to CBC, this means that when cipher-text block sequences are reordered, decryption output is altered. It is possible because of the fact that for a block to be decrypted, it depends entirely on the decryption of the previous blocks.

Discuss the similarities and differences between Cipher Feedback (CFB) and Cipher-Blocking Chain (CBC)

The cipher feedback relies on confusion as a way of encryption while the cipher block chain relies on both confusion and diffusion.While the cipher feedback uses the XOR function for the conversion of the plain text into cipher text making it one of the reasons easy to reverse the XORed bits, the cipher blocking chain does not use the XORed reversibility algorithm making it hard to reverse the encrypted text.

Both have different methods of encryption. While the cipher block chain uses the one block of text at a time for encryption, the cipher feedback technique involves both the encryption and decryption of one byte of the text at a time. The cryptographer can easily decipher a CBC code because when a string of blocks appear to be the same, he can use a predictive pattern as compared to the CFB. The cipher feedback uses different keys for each byte while the cipher lock chain uses the same key to encrypt each block. The cipher block-chaining mode employs the use of an initialization vector (IV), and then chains all the remaining blocks together by means of XOR to the encryption blocks output with the plaintext block that follows next. The Initialization Vector needs not to be secret and should be shared or communicated to the receiver. It is essential to note that each new plain text should have a new IV generated so that its value is not influenced or affected by any malicious use on it.

On the other hand, the cipher feedback mode transmits messages with less bits compared to block-size, for instance, it is used for used during interactive terminal sessions. By way of explanation, the CFB permits the DES to be utilized as a stream cipher. It contains error propagation properties just like CBC. The science behind the cipher feedback mode is that it works by coding an IV to come up with an output block, followed by sole ORs succeeding bits of the output block with back-to-back bits of plaintext, which result in to the ciphertext.