Feistel cipher — Safekipedia Adventurer

A Feistel cipher is a special way to keep information safe. It is used in a part of science called cryptography. The idea was created by a scientist named Horst Feistel from Germany. He worked for a big company called IBM. This method helps make 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. Russia used GOST (aka Magma). Newer systems like Blowfish and Twofish also use this idea.

One nice 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 ways to keep information safe use something called Feistel networks. These networks were first used in a cipher named Lucifer. It was created by Horst Feistel and Don Coppersmith in 1973. Later, the U.S. government used a version of this called DES in 1976. This helped make Feistel networks very important for keeping data safe. The way these networks were designed made them easier to build with the technology of 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. This means 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

Many cryptographers have studied the Feistel cipher structure.

Michael Luby and Charles Rackoff discovered that using a special function, just three steps can make the cipher very secure, and four steps make it even more secure. This is why Feistel ciphers are also called Luby–Rackoff block ciphers. Later studies helped us understand these ciphers better.

Construction details

A Feistel cipher is a way to create secure codes, or ciphers, to keep information safe. 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 use almost the same steps. The only 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.