Horst Feistel (January 30, 1915[1] – November 14, 1990) was a German-American cryptographer who worked on the design of ciphers at IBM, initiating research that culminated in the development of the Data Encryption Standard (DES) in the 1970s.
The structure used in DES, called a Feistel network, is commonly used in many block ciphers.
The following day he was granted a security clearance and began work for the US Air Force Cambridge Research Center (AFCRC) on Identification Friend or Foe (IFF) devices until the 1950s.
[5] His research at IBM led to the development of the Lucifer and Data Encryption Standard (DES) ciphers.
Feistel was one of the earliest non-government researchers to study the design and theory of block ciphers.