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Encyclopedia > Block size (cryptography)

In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. Block ciphers operate on a fixed length string of bits. The length of this bit string is the block size. Both the input (plaintext) and output (ciphertext) are the same length; the output cannot be shorter than the input — this is logically required by the Pigeonhole principle and the fact that the cipher must be invertible — and it is simply undesirable for the output to be longer than the input. Cryptography has had a long and colourful history. ... Symmetric-key algorithms are a class of algorithms for cryptography that use trivially related cryptographic keys for both decryption and encryption. ... This article is about algorithms for encryption and decryption. ... The operation of A5/1, a LFSR-based stream cipher used to encrypt mobile phone conversations. ... In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... This article is about the unit of information. ... The plain text term has a different meaning. ... This article is about algorithms for encryption and decryption. ... The inspiration for the name of the principle: pigeons in holes. ...


Until the announcement of NIST's AES contest, the majority of block ciphers followed the example of the DES in using a block size of 64 bits (8 bytes). However the Birthday paradox tells us that after accumulating a number of blocks equal to the square root of the total number possible, there will be an approximately 50% chance of two or more being the same, which would start to leak information about the message contents. Thus even when used with a proper encryption mode, only 2^{32} times 8 B = 32 GB of data can be safely sent under one key. In practice we want odds a lot better than 50%, so we are restricted to much less data - say a few hundred megabytes. Once that seemed like a fair amount of data, but today it is easily exceeded. (If the cipher mode does not properly randomise the input, the limit is even worse). As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... On January 2, 1997 the National Institute of Standards and Technology, or NIST, called for cryptographers to propose a new standard block cipher for United States Government use in non-classified but sensitive applications. ... General Designer(s) IBM First published 1975 (January 1977 as the standard) Derived from Lucifer (cipher) Cipher(s) based on this design Triple DES, G-DES, DES-X, LOKI89, ICE Algorithm detail Block size(s) 64 bits Key size(s) 56 bits Structure Feistel network Number of rounds 16 Best... A byte is commonly used as a unit of storage measurement in computers, regardless of the type of data being stored. ... The birthday paradox states that if there are 23 or more people in a room then there is a chance of more than 50% that at least two of them will have the same birthday. ... In mathematics, the principal square root of a non-negative real number is denoted and represents the non-negative real number whose square (the result of multiplying the number by itself) is For example, since This example suggests how square roots can arise when solving quadratic equations such as or... In cryptography, a block cipher operates on blocks of fixed length, often 64 or 128 bits. ...


Consequently AES candidates were required to support a block length of 128 bits (16 bytes). This should be acceptable for up to 2^{64} times 16 B = 256 Exabytes of data, and should suffice for quite a few years to come. The winner of the AES contest, Rijndael, supports block sizes of 128, 192, and 256 bits, although the extra block sizes were not adopted by the AES standard. An exabyte (derived from the SI prefix exa-, and abbreviated as EB) is a unit of information or computer storage equal to approximately one quintillion bytes. ... General Designer(s) Vincent Rijmen and Joan Daemen First published 1998 Derived from Square (cipher) Cipher(s) based on this design Crypton (cypher), Anubis (cipher), GRAND CRU Algorithm detail Block size(s) 128 bits note Key size(s) 128, 192 or 256 bits note Structure Substitution-permutation network Number of...


A few block ciphers, such as RC5, support a variable block size. The Luby-Rackoff construction and the Outerbridge construction can both increase the effective block size of a cipher. General Designer(s) Ron Rivest First published 1994 Derived from - Cipher(s) based on this design RC6, Akelarre Algorithm detail Block size(s) 32, 64 or 128 bits (64 suggested) Key size(s) 0 to 2040 bits (128 suggested) Structure Feistel network Number of rounds 12 suggested originally Best cryptanalysis...


Joan Daemen's 3-Way has an unusual 96-bit block size. In cryptography, 3-Way is a block cipher designed in 1994 by Joan Daemen, who also (with Vincent Rijmen) designed Rijndael, the winner of NISTs Advanced Encryption Standard (AES) contest. ...



Block ciphers edit
Algorithms: 3-Way | AES | Akelarre | Anubis | Blowfish | Camellia | CAST-128 | CAST-256 | CMEA | CS-Cipher | DEAL | DES | DES-X | FEAL | FOX | FROG | G-DES | GOST | ICE | IDEA | Iraqi | KASUMI | KHAZAD | Khufu and Khafre | LOKI89/91 | LOKI97 | Lucifer | MacGuffin | Madryga | MAGENTA | MARS | MISTY1 | MMB | NewDES | Noekeon | RC2 | RC5 | RC6 | REDOC | Red Pike | S-1 | SAFER | SEED | Serpent | SHACAL | SHARK | Skipjack | Square | TEA | Triple DES | Twofish | XTEA
Design: Feistel network | Key schedule | Product cipher | S-box | SPN   Attacks: Brute force | Linear / Differential cryptanalysis | Mod n | Related key | XSL   Standardization: AES process | CRYPTREC | NESSIE   Misc: Avalanche effect | Block size | IV | Key size | Modes of operation | Piling-up lemma | Weak key

  Results from FactBites:
 
A Variable Size Core for Block Cipher Cryptography (3874 words)
block cipher which can be expanded arbitrarily, to the byte, at ciphering time, we are necessarily limited to operations which can be applied byte-by-byte.
If the cipher block size is small (under 64 bytes), and if the plaintext is not randomized, and if dynamic keying is not used, and if the ciphering key is not changed frequently, it may be possible to build a codebook of block values with their intended meanings.
Once the block size is at least, say, 64 bytes, we expect the amount of uniqueness in each block to exceed anyone's ability to collect and form a codebook.
Block size (cryptography) - Wikipedia, the free encyclopedia (388 words)
In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers.
Until the announcement of NIST's AES contest, the majority of block ciphers followed the example of the DES in using a block size of 64 bits (8 bytes).
The winner of the AES contest, Rijndael, supports block sizes of 128, 192, and 256 bits, although the extra block sizes were not adopted by the AES standard.
  More results at FactBites »

 
 

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