Week 1 - Feistel Structure

Question 1

What is Feistel Structure?

Answer 1

A framework for block cyphers.
Message spilt into 2 parts and encryption is repeated using a functions and round keys

Question 2

How is a Feistel structure executed?

Answer 2

1. plaintext is split into two blocks left(L) and right (R)
2. a function is applied to the R half with a round key
3. result is XORed with L half
4. haves are swapped
5. this is repeated for multiple rounds

function = f(ki, R)

Question 3

What happens with Main encryption key?

Answer 3

it is used to generate round keys for each round

Question 4

What is the purpose of performing multiple rounds in a Feistel cypher?

Answer 4

Multiple rounds add complexity, making the encryption process harder to reverse without the key

Question 5

How does decryption work ?

Answer 5

ame process but the round keys are applied in reverse order.