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A Feistel network is a cryptographic technique used in the construction of block cipher-based algorithms and mechanisms. Designed by IBM employees Horst Feistel and Don Coppersmith, the first use of the Feistel network was in Lucifer block cipher.
A Feistel network is also known as a Feistel cipher.
A Feistel network implements a series of iterative ciphers on a block of data and is generally designed for block ciphers that encrypt large quantities of data. A Feistel network works by splitting the data block into two equal pieces and applying encryption in multiple rounds. Each round implements permutation and combinations derived from the primary function or key. The number of rounds varies for each cipher that implements a Feistel network.
Moreover, as a reversible algorithm, a Feistel network produces the same output until the input is the same.