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Настоящий стандарт устанавливает единый алгоритм криптографического преобразования для систем обработки информации в сетях электронных вычислительных машин (ЭВМ), отдельных вычислительных комплексах и ЭВМ,
который определяет правила шифрования данных и выработки имитовставки.

In cryptography, a Feistel cipher (also known as Luby–Rackoff block cipher) is a symmetric
structure used in the construction of block ciphers, named after the German-born physicist and
cryptographer Horst Feistel who did pioneering research while working for IBM (USA); it is also commonly
known as a Feistel network. A large proportion of block ciphers use the scheme, including the US Data Encryption
Standard, the Soviet/Russian GOST and the more recent Blowfish and Twofish ciphers. In a Feistel cipher, encryption
and decryption are very similar operations, and both consist of iteratively running a function called a "round function"
a fixed number of times.