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Encyclopedia > Key schedule
The key-schedule of DES ("<<<" denotes a left rotation)

In cryptography, the so-called product ciphers are a certain kind of ciphers, where the (de-)ciphering of data is done in "rounds". The general setup of each round is the same, except for some hard-coded parameters and a part of the cipher key, called a subkey. A key schedule is an algorithm that, given the key, calculates the subkeys for these rounds. Key schedule of DES This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... Key schedule of DES This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek ÎºÏÏ…Ï€Ï„ÏŒÏ‚ kryptÃ³s hidden, and the verb Î³ÏÎ¬Ï†Ï‰ grÃ¡fo write) is the study of message secrecy. ... In cryptography, a product cipher is a popular type of block cipher that works by executing in sequence a number of simple transformations such as substitution, permutation, and modular arithmetic. ... A key is a piece of information that controls the operation of a cryptography algorithm. ...

## Some types of key schedules GA_googleFillSlot("encyclopedia_square");

• Some ciphers have simple key schedules. For example, the block cipher TEA simply splits the 128-bit key into four 32-bit pieces and uses them repeatedly in successive rounds.
• DES uses a key schedule where the 56 bit key is divided into two 28-bit halves; each half is thereafter treated separately. In successive rounds, both halves are rotated left by one or two bits (specified for each round), and then 48 subkey bits are selected by Permuted Choice 2 (PC-2) — 24 bits from the left half, and 24 from the right. The rotations mean that a different set of bits is used in each subkey; each bit is used in approximately 14 out of the 16 subkeys.
• In an effort to avoid simple relationships between the cipher key and the subkeys, many modern ciphers use much more elaborate key schedules, algorithms that use a one-way function to generate an "expanded key" from which subkeys are drawn. Some ciphers, such as Rijndael (AES) and Blowfish, use parts of the cipher algorithm itself for this key expansion, sometimes initialized with some "nothing up my sleeve numbers". Other ciphers, such as RC5, expand keys with functions that are somewhat or completely different from the encryption functions.

General Designer(s) Roger Needham and David Wheeler First published 1994 Derived from - Cipher(s) based on this design XTEA Algorithm detail Block size(s) 64 bits Key size(s) 128 bits Structure Feistel network Number of rounds variable; recommended 64 Feistel rounds; 32 cycles Best cryptanalysis TEA suffers from... The Data Encryption Standard (DES) is a cipher (a method for encrypting information) selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976, and which has subsequently enjoyed widespread use internationally. ... Unsolved problems in computer science: Do one-way functions exist? A one-way function is a function that is easy to compute but hard to invert. ... This article or section is in need of attention from an expert on the subject. ... General Designer(s) Bruce Schneier First published 1993 Derived from - Cipher(s) based on this design Twofish Algorithm detail Block size(s) 64 bits Key size(s) 32-448 bits in steps of 8 bits; default 128 bits Structure Feistel network Number of rounds 16 Best cryptanalysis Four rounds of... Nothing up my sleeve numbers are the the opposite extreme of Chaitin-Kolmogorov randomness in that they appear to be random by statistical tests but are created with minimum entropy. ... RC5 is a block cipher notable for its simplicity. ...

## Notes

Knudsen and Mathiassen (2004) give some experimental evidence that indicate that the key schedule plays a part in providing strength against linear and differential cryptanalysis. For toy Feistel ciphers, it was observed that those with complex and well-designed key schedules can reach a uniform distribution for the probabilities of differentials and linear hulls faster than those with poorly-designed key schedules. Lars R. Knudsen Lars Ramkilde Knudsen (born February 21, 1962) is a Danish researcher in cryptography, particularly interested in the design and analysis of block ciphers, hash functions and message authentication codes (MACs). ... In cryptography, linear cryptanalysis is a general form of cryptanalysis based on finding affine approximations to the action of a cipher. ... Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. ... Feistel cipher - Wikipedia /**/ @import /skins-1. ... Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. ... In cryptography, linear cryptanalysis is a general form of cryptanalysis based on finding affine approximations to the action of a cipher. ...

In cryptography, a related-key attack is any form of cryptanalysis where the attacker can observe the operation of a cipher under several different keys whose values are initially unknown, but where some mathematical relationship connecting the keys is known to the attacker. ...

## References

• Lars R. Knudsen and John Erik Mathiassen, On the Role of Key Schedules in Attacks on Iterated Ciphers, ESORICS 2004, pp322–334.
Block ciphers
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Design: Feistel network | Key schedule | Product cipher | S-box | SPN

Standardization: AES process | CRYPTREC | NESSIE

Misc: Avalanche effect | Block size | IV | Key size | Modes of operation | Piling-up lemma | Weak key The Advanced Encryption Standard (AES), the block cipher ratified as a standard by National Institute of Standards and Technology (NIST), was chosen using a process markedly more open and transparent than its predecessor, the ageing Data Encryption Standard (DES). ... CRYPTREC is the Cryptography Research and Evaluation Committee set up by the Japanese Government to evaluate and recommend cryptographic techniques for government and industrial use. ... NESSIE (New European Schemes for Signatures, Integrity and Encryption) was a European research project funded from 2000&#8211;2003 to identify secure cryptographic primitives. ... This article is about cryptography; for other meanings, see snowball effect. ... In modern cryptography, symmetric key ciphers are generally divided into stream ciphers and block ciphers. ... In cryptography, an initialization vector (IV) is a block of bits that is required to allow a stream cipher or a block cipher executed in any of several streaming modes of operation to produce a unique stream independent from other streams produced by the same encryption key, without having to... In cryptography, the key size (alternatively key length) is a measure of the number of possible keys which can be used in a cipher. ... In cryptography, a block cipher operates on blocks of fixed length, often 64 or 128 bits. ... In cryptanalysis, the piling-up lemma is a principle used in linear cryptanalysis to construct linear approximations to the action of block ciphers. ... In cryptography, a weak key is a key which when used with a specific cipher, makes the cipher behave in some undesirable way. ...

Cryptography
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History of cryptography | Cryptanalysis | Cryptography portal | Topics in cryptography
Symmetric-key algorithm | Block cipher | Stream cipher | Public-key cryptography | Cryptographic hash function | Message authentication code | Random numbers

Results from FactBites:

 Key (cryptography) - Wikipedia, the free encyclopedia (854 words) Keys are also used in other cryptographic algorithms, such as digital signature schemes and keyed-hash functions (also known as MACs), often used for authentication. A newer class of "public key" cryptographic algorithms was discovered in the 1970s which use a pair of keys, one to encrypt and one to decrypt. When a password (or passphrase) is used as an encryption key, well-designed cryptosystems first run it through a key-derivation algorithm which adds salt and reduces or expands it to the key length desired, for example by reducing a long phrase into a 128-bit value suitable for use in a block cipher.
 Key schedule - definition of Key schedule in Encyclopedia (173 words) In cryptography, the algorithm for computing the subkeys for each round in a product cipher from the encryption (or decryption) key is called the key schedule. For toy Feistel ciphers, it was observed that those with complex and well-designed key schedules can reach a uniform distribution for the probabilities of differentials and linear hulls faster than those with poorly-designed key schedules. Lars R. Knudsen and John Erik Mathiassen, On the Role of Key Schedules in Attacks on Iterated Ciphers, ESORICS 2004, pp322–334.
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