computer science

Horst Feistel

Horst Feistel is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Horst Feistel rather than just read about it. In short: Horst Feistel (January 30, 1915 – 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.

Key takeaways

Horst Feistel belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Horst Feistel to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Horst Feistel from memory before moving on to harder problems.

Reference excerpt

Horst Feistel (January 30, 1915 – 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.

Life and work Feistel was born in Berlin, Germany in 1915, and moved to the United States in 1934. During World War II, he was placed under house arrest, but gained US citizenship on 31 January 1944. 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. He was subsequently employed at MIT's Lincoln Laboratory, then the MITRE corporation. In 1968, Feistel became a Research Staff Member at the IBM T.J Watson Center. During his time there he received an award for his cryptographic work. In 1971, he patented the block cipher cryptographic system at IBM. 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. Feistel lent his name to the Feistel network construction, a common method for constructing block ciphers (for example DES). Feistel obtained a bachelor's degree at MIT, and his master's at Harvard, both in physics. He married Leona (Gage) in 1945, with whom he had a daughter, Peggy.

Notes

References Whitfield Diffie, Susan Landau (1998). Privacy on the Line: The Politics of Wiretapping and Encryption. Horst Feistel, "Cryptography and Computer Privacy." Scientific American, Vol. 228, No. 5, 1973. (JPEG format scanned) Horst Feistel, H, W. Notz, J. Lynn Smith. "Some cryptographic techniques for machine-to-machine data communications." IEEE Proceedings, 63(11), 1545–1554, 1975. Levy, Steven. Crypto: How the Code Rebels Beat the Government—Saving Privacy in the Digital Age, 2001.

External links "Genealogical notes for Horst Feistel". Archived from the original on 2016-03-04. In praise of the Feistel network - MIT Technology Review

Worked examples

Example 1 — a first encounter with Horst Feistel

Start with the simplest possible case. Write down what Horst Feistel claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Horst Feistel before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Horst Feistel ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Horst Feistel

In research: Horst Feistel appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Horst Feistel in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Horst Feistel is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1915 births, 1990 deaths, Emigrants from Nazi Germany to the United States, so understanding it makes those chapters shorter.
In everyday life: Look for Horst Feistel outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Horst Feistel in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Horst Feistel means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Horst Feistel out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Horst Feistel in simple terms?

Why does Horst Feistel matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Horst Feistel?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Horst Feistel.