In a Feistel cipher, the two halves of the block are swapped in each round .

What does this provide?

A . Diffusion

B. Confusion

C. Avalanche

D. Substitution

**Answer: **B

Explanation:

Confusion

https://en.wikipedia.org/wiki/Confusion_and_diffusion#Definition

Confusion means that each binary digit (bit) of the ciphertext should depend on several parts of the key, obscuring the connections between the two.

The property of confusion hides the relationship between the ciphertext and the key.

This property makes it difficult to find the key from the ciphertext and if a single bit in a key is changed, the calculation of the values of most or all of the bits in the ciphertext will be affected.

Confusion increases the ambiguity of ciphertext and it is used by both block and stream ciphers.

Incorrect answer:

Avalanche – The avalanche effect is the desirable property of cryptographic algorithms, typically block ciphers and cryptographic hash functions, wherein if an input is changed slightly (for example, flipping a single bit), the output changes significantly (e.g., half the output bits flip). In the case of high-quality block ciphers, such a small change in either the key or the plaintext should cause a drastic change in the ciphertext. The actual term was first used by Horst Feistel, although the concept dates back to at least Shannon’s diffusion.

Diffusion – Diffusion means that if we change a single bit of the plaintext, then (statistically)

half of the bits in the ciphertext should change, and similarly, if we change one bit of the ciphertext, then approximately one half of the plaintext bits should change.[2] Since a bit can have only two states, when they are all re-evaluated and changed from one seemingly random position to another, half of the bits will have changed state.

Substitution – Substitution technique is a classical encryption technique where the characters present in the original message are replaced by the other characters or numbers or by symbols.