Feistel network

So, let's imagine that you have a secret message that you don't want anyone else to read. You could just hide it, but if someone found it, they could read it easily. That's not very secure! So, you need to figure out a way to turn your secret message into gibberish that only you can unscramble.

A feistel network is like a secret code that takes your message and scrambles it up, making it look like nonsense. But it's not just a simple scramble - a feistel network is a complicated way of turning your message into a code that only you can unscramble.

It works like this: you take your message and split it in half. Then, you apply a set of rules to one half, and another set of rules to the other half. These rules are like secret codes that change the letters in your message around.

After you've applied the rules to both halves, you switch them around - so the first half of your message becomes the second half, and the second half becomes the first. Then, you apply the rules again to both halves.

You keep doing this over and over, switching the halves and applying the rules, until your message is just a bunch of scrambled letters that nobody can read. This process is called "rounds" - you go through each round and scramble your message some more.

But, even though your message looks like gibberish, you can unscramble it because you know the secret rules that were used to scramble it up. You just reverse the process - you take the scrambled message, apply the rules in reverse order, switch the halves back and forth, and eventually you end up with the original message.

So, a feistel network is a way of scrambling up your message so that it's safe from prying eyes - but you can unscramble it easily because you know the secret rules that were used to scramble it in the first place.