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It's there to facilitate a simple implementation. As there is no key addition applied afterwards, the final swapping of the halves does not contribute towards security. The Feistel cipher entry on tutorialspoint explains: Decryption Process The process of decryption in Feistel cipher is almost similar. Instead of starting with a block of plaintext,...


Let's look at a picture of a generic feistel cipher Notice that no keying material is used during or after that final swap. So, we can conclude that the final swap does not impact security at all. So, why include it? It is so that all rounds will be identical. This could help with some implementations. That is all.


It depends on the block cipher in question - specifically its key schedule. Knowing any round key of AES-128 would let you calculate the key, because the schedule is reversible. OTOH, e.g. TEA would retain secrecy of most of the key and might remain secure, because its round keys are small enough parts of the key. In the case of DES, it is weak enough to be ...


The simple answer is "Because its an SPN cipher". What is difference between Feistel and SPN? SPN operates on whole data in one round, where as Feistel divides data into N parts where N>=2 , then operate upon X parts where 0 In balanced, data is divided in Two parts i.e N = 2, and X=1 (example is camellia cipher) In Unbalanced, data is divided in more ...

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