From the course: Symmetric Cryptography Essential Training

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Feistel ciphers

Feistel ciphers

From the course: Symmetric Cryptography Essential Training

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Feistel ciphers

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- [Instructor] While they're not used in every case, Feistel networks are fundamental structures for block ciphers. They're a really nice way of combining permuatations and substitutions, which are applied to the plaintext repeatedly. Feistel networks are made up of rounds. Each time this package of permuatations and substitutions is applied to a plaintext block, that's one of those rounds. And then the actual set of transformations that's applied each round is called the round function. Within each of these rounds, Feistel networks use the subkey, or round key, which are smaller keys derived from the main key, with a key schedule. The only difference between encryption and decryption is which round key we use at each step. We essentially reverse the order of the round keys to do the decryption. One interesting property of Feistel networks is that it doesn't really matter how the round function works. The encryption will be reversible either way. Security of Feistel networks is…

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