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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'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,...


A block cipher mode is an algorithm used along with a block algorithm to encrypt arbitrary size plaintext, providing both confidentiality and authentication. A single block cipher operates only on a fixed block length. It is not alone enough to encrypt larger plaintexts. However, a single block encryption can work as a black box in the Random Oracle Theory. ...


The block cipher itself is used as a black box for any mode of operation. The internal design - including if the block cipher uses a Feistel network - is completely tranparent to the mode of operation. The only thing that matters for the mode of operation is the block size of the block cipher. This, together with any usage limitations, limits the ...

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