Question

Write a short notes on i) Feistel Block Cipher structure ii)Block cipher Design Principles​

Answer 1

Answer:

i.) The encryption process uses the Feistel structure consisting multiple rounds of processing of the plaintext, each round consisting of a “substitution” step followed by a permutation step. The input block to each round is divided into two halves that can be denoted as L and R for the left half and the right half.

ii.) BLOCK CIPHER DESIGN PRINCIPLES

Although much progress has been made in designing block ciphers that are cryptographically strong, the basic principles have not changed all that much since the work of Feistel and the DES design team in the early 1970s. It is useful to begin this discussion by looking at the published design criteria used in the DES effort. Then we look at three critical aspects of block cipher design: the number of rounds, design of the function F, and key scheduling.