block ciphers

In cryptography, a block cipher is a deterministic algorithm processing on fixed-length data string. Which called a block, with an unvarying transformation that is specified by a symmetric key. Block ciphers run as important elementary components in the design of many cryptographic protocols, and are used to implement encryption of bulk data.

The design of modern block ciphers is based on the definition of an iterated product cipher. Claude Shannon ,In 1949 on Communication Theory of Secrecy Systems, he analyzed product ciphers and suggested them as a way effectively improving security by combining simple operations such as permutations and substitutions

Iterated product ciphers perform encryption in multiple rounds, in each rounds it uses a different subkey derived from the original key. One famous block ciphers named a Feistel network after Horst Feistel, is notably implemented in the DES cipher. Many other implementations of of block ciphers, such as the AES, are categorized as substitution–permutation networks.

The publication of the DES cipher which is designed by the United States National Bureau of Standards (subsequently the U.S. National Institute of Standards and Technology, NIST) in was fundamental in the public understanding of modern block cipher.

As of 2016 there is a palette of attack techniques against which a block cipher must be secure, in addition to being robust against brute-force attacks.

The design of des cipher also influenced the development of cryptanalytic attacks

There are multiple modes modes of operation for a block ciper, . However, block ciphers may also feature as building blocks in other cryptographic protocols, such as universal hash functions and pseudo-random number generators.