In
cryptography, a
Feistel 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
Data Encryption Standard (DES). The Feistel structure has the advantage that
encryption and
decryption operations are very similar, even identical in some cases, requiring only a reversal of the
key schedule. Therefore the size of the code or circuitry required to implement such a cipher is nearly halved.