Feistel cipher — Safekipedia Discoverer

A Feistel cipher is a special way to keep information safe, used in a part of science called cryptography. It was named after Horst Feistel, a smart scientist from Germany who worked for a big company called IBM. This method helps build strong ways to lock up data, called block ciphers.

Many important systems use Feistel ciphers to protect secrets. For example, the United States used one called the Data Encryption Standard, and Russia used GOST (aka Magma). Newer systems like Blowfish and Twofish also use this idea.

One cool thing about Feistel ciphers is that locking information away and unlocking it look almost the same. They both use a small job called a "round function" round function many times to keep data safe but still easy to read when needed.

History

Many modern encryption methods use something called Feistel networks. These networks were first used in a cipher called Lucifer, created by Horst Feistel and Don Coppersmith in 1973. Later, the U.S. government adopted a version of this called DES in 1976, which helped make Feistel networks very important in security technology. The design of these networks made them easier to build with the technology available at that time.

Main article: DES

Design

A Feistel network uses something called a "round function." This function takes two pieces of information — a block of data and a special key — and mixes them together. In each step, the round function works on half of the data, and its result is combined with the other half. This process is repeated many times to keep the data safe.

One big benefit of Feistel networks is that they can always be undone, meaning encrypted data can be decrypted again, even if the round function itself isn’t very simple. Also, locking and unlocking the data look almost the same, which makes the system easier to build. This helps save space and keeps things running smoothly.

Theoretical work

The structure of Feistel ciphers has been studied a lot by cryptographers.

Michael Luby and Charles Rackoff showed that if a special kind of function is used in the cipher, just three steps are enough to make the cipher very safe, and four steps make it even safer. This important discovery is why Feistel ciphers are sometimes called Luby–Rackoff block ciphers. Later work has helped understand these ciphers even better.

Construction details

A Feistel cipher is a way to build secure codes, or ciphers, for protecting information. It works by splitting a block of data into two parts. For each step, or "round," it changes these parts using a special function and a secret key. This process is repeated many times to make the data very hard to read.

Both encoding and decoding in a Feistel cipher follow very similar steps. The main difference is that the order of the secret keys is reversed when decoding. This makes it easy to both hide and uncover the information safely.

List of Feistel ciphers

Feistel ciphers are special types of encryption used to keep information safe. Many famous encryption methods use this structure. Some of these include: