Block Cipher

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

The modern design of block ciphers is based on the concept of an iterated product cipher. Product ciphers were suggested and analyzed by Claude Shannon in his seminal 1949 publication Communication Theory of Secrecy Systems as a means to effectively improve security by combining simple operations such as substitutions and permutations. Iterated product ciphers carry out encryption in multiple rounds, each which uses a different subkey derived from the original key. A widespread implementation of such ciphers is called a Feistel network, named after Horst Feistel, and notably implemented in the DES cipher. Many other realizations of block ciphers, such as the AES, are classified as substitution-permutation networks.

The publication of the DES cipher by the U.S. National Bureau of Standards (now National Institute of Standards and Technology, NIST) in 1977 was fundamental in the public understanding of modern block cipher design. In the same way, it influenced the academic development of cryptanalytic attacks. Both differential and linear cryptanalysis arose out of studies on the DES design. Today, there is a palette of attack techniques that a block cipher must be secure against, in addition to being robust against brute force attacks.

Even a secure block cipher is suitable only for the encryption of a single block under a fixed key. A multitude of modes of operations have been designed to allow their repeated use in a secure way, commonly to achieve the security goals of encryption and authentication. However, block ciphers may also be used as building blocks in other cryptographic protocols, such as universal hash functions and pseudo-random number generators.

Read more about Block CipherDefinition, Modes of Operation, Padding, Practical Evaluation, Relation To Other Cryptographic Primitives

Other articles related to "ciphers, cipher, block cipher, block ciphers, block, blocks":

Slide Attack
... is a form of cryptanalysis designed to deal with the prevailing idea that even weak ciphers can become very strong by increasing the number of rounds, which can ward off a differential ... way as to make the number of rounds in a cipher irrelevant ... Rather than looking at the data-randomizing aspects of the block cipher, the slide attack works by analyzing the key schedule and exploiting weaknesses in it to break the cipher ...
Message Authentication Codes - Standards
... ISO/IEC 9797-1 Mechanisms using a block cipher ISO/IEC 9797-2 Mechanisms using a dedicated hash-function ISO/IEC 9797-1 and -2 define generic models and algorithms ... to ISO/IEC 9797-1 MAC algorithm 1 with padding method 1 and a block cipher algorithm of DES ...
Block Cipher - Relation To Other Cryptographic Primitives
... Block ciphers can be used to build other cryptographic primitives, such as those below ... Stream ciphers can be built using block ciphers ... OFB-mode and CTR mode are block modes that turn a block cipher into a stream cipher ...
Initialization Vector - Motivation
... A block cipher is one of the most basic primitives in cryptography, and frequently used for data encryption ... However, by itself, it can only be used to encode a data block of a predefined size, called the block size ... The key, which is given as one input to the cipher, defines the mapping between plaintext and ciphertext ...
Block Cipher Modes Of Operation - Output Feedback (OFB)
... The output feedback (OFB) mode makes a block cipher into a synchronous stream cipher ... It generates keystream blocks, which are then XORed with the plaintext blocks to get the ciphertext ... Just as with other stream ciphers, flipping a bit in the ciphertext produces a flipped bit in the plaintext at the same location ...

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