Feistel Networks are building blocks of many stream cipher notably DES, SwordFish etc, wherein one performs a fixed number of rounds of the feistel network, for both excryptopn and decrypton. Feistel Network The abbreviations are as follows, F: Round function K i : Subkey for round i L i : Left half of the intermediate value at round i, L 0 would be the left half of clear text. R i : Right half of the intermediate value at round i, R 0 would be the right half of clear text. Micheal Luby and Charles Rackoff proved that, If the round function is a cryptographically secure pseudorandom function, then 3 rounds are sufficient to make the block cipher a pseudorandom permutation, while 4 rounds are sufficient to make it a "strong" pseudorandom permutation. Strong psuedorandom permutation means that it remains pseudorandom even to an adversary who gets oracle access to its inverse permutation. Note that in one round of a feistal network, only the left half of the cleartext is enc...
Universe from my perspective..