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.