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A cryptographer who worked at IBM in the 70s. While creating a cipher for IBM, he invented a new method of designing such ciphers, now known as Feistel Ciphers or Feistel Networks. This culminated in the designs of Lucifer and later DES, which was designated for use by the US Government for securing non-classified data for 25 years (1977-2002), and is and was used around the world for securing commercial and personal traffic, including many banks.

DES has finally been replaced by Rijndael, which won a competition out of 15 different ciphers to become the AES (Advanced Encryption Standard). Interestingly enough, Rijndael is not a Feistel cipher.

Horst Feistel is one of the most important figures of modern cryptography. The ubiquitous DES cipher was primarily his invention, and the techniques he developed are still used in most modern block ciphers.

Feistel was born in Berlin, Germany in 1915, and emigrated to the United States in 1934. Here, he earned a Bachelor's degree from MIT, and a Master's from Harvard, both in Physics. Despite this, his true calling was cryptography. Unfortunately, his German background aroused suspicion, and he was harassed by the NSA, who were jealously protected the domain of crypto. He worked on crypto systems for the US Air Force and Mitre Corp, both of whom were pressured to halt his research. Eventually, he was able to find a research position at IBM's Thomas J. Watson Laboratory.

It was at IBM where Feistel developed the Lucifer cipher, in the early 1970s. The Lucifer algorithm he developed takes 64 bits of text and 64 bits of key material and produces 64 bits of cipher text. The cipher text and the key can be used to recover plaintext, making it a symmetric cipher. The specific method he used to scramble the data became known as a Feistel Network.

Lucifer was widely considered to be one of the most secure crypto systems of its time. After a few tweaks mandated by the NSA, such as scaling back the key size to 56 bits, Lucifer was dubbed Data Encryption Standard (DES) for the United States. DES remains in wide use today.

Feistel died in 1990.

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