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Reference.org
Feistel cipher
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<p>In <a href="/facts/Cryptography/e94PEVau">cryptography</a>, a Feistel cipher (also known as Luby–Rackoff block cipher) is a <a href="/facts/Symmetric-key_algorithm/5zfe0b76">symmetric structure</a> used in the construction of <a href="/facts/Block_cipher/MJywAyfQ">block ciphers</a>, named after the <a href="/facts/Germany/paluuWBX">German</a>-born <a href="/facts/Physicist/cQcgvSIm">physicist</a> and cryptographer <a href="/facts/Horst_Feistel/fDRt2THf">Horst Feistel</a>, who did pioneering research while working for <a href="/facts/IBM/QszA7nwd">IBM</a>; it is also commonly known as a Feistel network. A large number of <a href="/facts/Block_cipher/MJywAyfQ">block ciphers</a> use the scheme, including the US <a href="/facts/Data_Encryption_Standard/STfBjTGb">Data Encryption Standard</a>, the Soviet/Russian <a href="/facts/GOST_(block_cipher)/AVDEpgqH">GOST</a> and the more recent <a href="/facts/Blowfish_(cipher)/H6fYatpd">Blowfish</a> and <a href="/facts/Twofish/T1pjlttA">Twofish</a> ciphers. In a Feistel cipher, encryption and decryption are very similar operations, and both consist of iteratively running a function called a "<a href="/facts/Round_(cryptography)/GDSequUg">round function</a>" a fixed number of times. </p>