Feistel Cipher Structure | Feistel network | Feistel cipher encrytion and decryption | 16 rounds of encryption and decryption in feistel cipher

Feistel Cipher Structure

Introduction

Feistel proposed a scheme to produce a block cipher using permutation and substitution alternatively. The inputs to the encryption algorithm are a plaintext block of length 2w bits and a key Ki. The plaintext block is divided into two halves, LE₀ and RE₀. The two halves of the data pass through rounds of processing and then combine to produce the ciphertext block.

Working of Feistel Cipher Structure

A substitution is performed on the left half of the data. This is done by applying a round function F to the right half of the data and then taking the exclusive-OR of the output of that function and the left half of the data. The round function has the same general structure for each round but is parameterized by the round subkey K_i. Permutation is performed that consists of the interchange of the two halves of the data. This structure is a particular form of the substitution-permutation network (SPN) proposed by Shannon.

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