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# Topic: Feistel cipher

 Q56: What is Feistel Cipher? In a Feistel cipher, the text being encrypted is split into two halves. A nice feature of a Feistel cipher is that encryption and decryption are structurally identical, though the subkeys used during encryption at each round are taken in reverse order during decryption. It is possible to design iterative ciphers that are not Feistel ciphers, yet whose encryption and decryption (after a certain re-ordering or re-calculation of variables) are structurally the same. www.x5.net /faqs/crypto/q56.html   (151 words)

 Measured Boolean Function Nonlinearity in Feistel Cipher Constructions MEASURED NONLINEARITY IN FEISTEL CONSTRUCTIONS Terry Ritter Ritter Software Engineering http://www.io.com/~ritter/ 1998-02-25 Abstract Nonlinearity is the number of bits which must change in the truth table of a Boolean function to reach the closest affine function, and thus is a measure of one kind of cipher strength. So the modern block cipher is a *construction* intended to *simulate* a keyed substitution of the desired size. So nonlinearity measures one form of cipher "strength." For cryptographic purposes, it is desired to take the nonlinearity of a substitution table to be the *minimum* of the nonlinearity values for each output bit in that table. www.ciphersbyritter.com /ARTS/FEISNONL.HTM   (714 words)

 Feistel cipher Information In cryptography, a Feistel cipher is a block cipher with a particular structure, named after IBM cryptographer Horst Feistel; it is also commonly known as a Feistel network. The Feistel structure has the advantage that encryption and decryption operations are very similar, even identical in some cases, requiring only a reversal of the key schedule. Many modern symmetric block ciphers are based on Feistel networks, and the structure and properties of Feistel ciphers have been extensively explored by cryptographers. www.bookrags.com /wiki/Feistel_cipher   (588 words)

 Feistel Ciphers and DES in Haskell. « codeland A Feistel network is a block cipher: that is, it’s a cipher that acts on fixed-length blocks. First, feistel is evaluated, with xor as the mixing function, f as the round function, block with “Initial Permutation” applied as the data block, and the input key schedule (note that we haven’t yet discussed how the key schedule is computed either). Once the Feistel network is applied, we apply another P-box, applyFp, the “Forward Permutation.” This is the inverse of “Initial Permutation.” In addition to this, we use a new function, merge’, to merge the results into a single ciphertext block while swapping L and R — which is a simple but subtle detail. vandreev.wordpress.com /2007/06/18/feistel-ciphers-and-des-in-haskell   (2064 words)

 security.rbaumann.net - Modern Techniques   (Site not responding. Last check: ) The idea behind a Feistel cipher is to create a cryptoographically stronger encryption by using a product cipher, which is the performing of two or more basic ciphers in sequence. Feistel proposed the use of a cipher that alternates substitution and permutations. The Feistel cipher security depends on the block size (the bigger the better, but also slower), key size (the bigger the better, matter of speed), number of rounds (typical 16 rounds), subkey generation algorithm (greater complexity leads to better security) and round function (higher complexity means greater resistance to cryptoanalysis). security.rbaumann.net /modtech.php?sel=2   (752 words)

 Feistel cipher In cryptography, a Feistel cipher is a block cipher with a particular structure, named after IBM cryptographer Horst Feistel; it is also commonly known as a Feistel network. The Feistel structure has the advantage that encryption and decryption operations are very similar, even identical in some cases, requiring only a reversal of the key schedule. Many modern symmetric block ciphers are based on Feistel networks, and the structure and properties of Feistel ciphers have been extensively explored by cryptographers. www.xasa.com /wiki/en/wikipedia/f/fe/feistel_cipher.html   (361 words)

 Feistel cipher   (Site not responding. Last check: ) In cryptography, a Feistel cipher is a block cipher with a particular structure, named after IBM cryptographer Horst Feistel; it is also commonly known as a Feistel network. The Feistel structure has the advantage that encryption and decryption operations are very similar, even identical in some cases, requiring only a reversal of the key schedule. Many modern symmetric block ciphers are based on Feistel networks, and the structure and properties of Feistel ciphers have been extensively explored by cryptographers. www.tocatch.info /en/Feistel_network.htm   (593 words)

 SSH - Support - Cryptography A-Z - Algorithms - Secret Key Cryptosystems OFB (output feedback): the cipher is used as a synchronous key-stream generator, whose output is XORed with the plaintext to obtain ciphertext, block by block. DES proved to be a very strong cipher and it took over a decade for any interesting cryptanalytical attacks against it to develop (not to underestimate the pioneering efforts that lead to this breakthrough). In the block cipher case the permutation is generated by the secret key and the key space might not cover all the possible permutations. www.ssh.com /support/cryptography/algorithms/symmetric.html   (3707 words)

 Feistel cipher   (Site not responding. Last check: ) In cryptography, a Feistel cipher is a block cipher with a particular structure, named after IBM cryptographer Horst Feistel ; it is also commonly known as aFeistel network. Feistel networks were first seen commercially in IBM's Lucifer cipher, designed by Feistel and DonCoppersmith. Many modern symmetric block ciphers are based on Feistel networks, and the structure and properties of Feistel ciphers havebeen extensively explored by cryptographers. www.therfcc.org /feistel-cipher-274212.html   (345 words)

 SSH - Support - Cryptography A-Z - Algorithms - Secret Key Cryptosystems OFB (output feedback): the cipher is used as a synchronous key-stream generator, whose output is XORed with the plaintext to obtain ciphertext, block by block. DES proved to be a very strong cipher and it took over a decade for any interesting cryptanalytical attacks against it to develop (not to underestimate the pioneering efforts that lead to this breakthrough). In the block cipher case the permutation is generated by the secret key and the key space might not cover all the possible permutations. www.ssh.fi /support/cryptography/algorithms/symmetric.html   (3707 words)

 ciphergoth.org: Mercy: A fast large block cipher for disk sector encryption   (Site not responding. Last check: ) We discuss the special requirements imposed on the underlying cipher of systems which encrypt each sector of a disk partition independently, and demonstrate a certificational weakness in some existing block ciphers including Bellare and Rogaway's 1999 proposal, proposing a new quantitative measure of avalanche. To address these needs, we present Mercy, a new block cipher accepting large (4096-bit) blocks, which uses a key-dependent state machine to build a bijective F function for a Feistel cipher. Ciphers by Ritter, including several patent-encumbered large block ciphers. www.ciphergoth.org /crypto/mercy   (413 words)

 Constructing Symmetric Ciphers Using the CAST Design Procedure CAST ciphers are based on the well-understood and extensively-analyzed framework of the Feistel cipher [17, 18] ­ the framework used in DES ­; but with a number of improvements (compared to DES) in both the round function and the key schedule which provide good cryptographic properties in fewer rounds than DES. The substitution layer in an SPN cipher is of critical importance to security since it is the primary source of nonlinearity in the algorithm (note that the permutation layer is a linear mapping from input to output). Ciphers designed around a new basis for cryptographic security (most notably RC-5 [47], based upon the conjectured security of data-dependent rotation operations) may prove to be extremely attractive candidates for DES replacement algorithms, but are not yet mature enough to be recommended for widespread use. cryptome.sabotage.org /cast.html   (12489 words)

 Cryptography Tutorials - Herong's Tutorial Notes - Cipher - DES Algorithm Block Cipher - An encryption scheme that "the clear text is broken up into blocks of fixed length, and encrypted one block at a time". Usually, a block cipher encrypts a block of clear text into a block of cipher text of the same length. In this case, a block cipher can be viewed as a simple substitute cipher with character size equal to the block size. www.herongyang.com /crypto/cipher_des.html   (316 words)

 Block Ciphers The general operation of all block ciphers is the same - a given number of bits of plaintext (a block) is encrypted into a block of ciphertext of the same size. Cipher feedback mode (CFB) differs from OFB in that the ciphertext (after the XOR step) is fed back rather than the output of the block cipher (before the XOR step). A block cipher operating in CFB mode can't be used as a random number generator. www.freesoft.org /CIE/Topics/143.htm   (1497 words)

 Concepts of Cryptography Cryptography, simply defined, is the art of combining some input data, called the plaintext, with a user-specified password to generate an encrypted output, called ciphertext, in such a way that, given the ciphertext, it is extremely difficult to recover the original plaintext without the encryption password in a reasonable amount of time. Various ciphers are documented in the Algorithms section. Stream ciphers can be thought of as seeded random number generators (with the seed being the key), with the random numbers being combined with the plaintext to generate ciphertext. kremlinencrypt.com /concepts.htm   (752 words)

 RSA Laboratories - 2.1.4.1 What is an iterated block cipher? In most cases, an increased number of rounds will improve the security offered by a block cipher, but for some ciphers the number of rounds required to achieve adequate security will be too large for the cipher to be practical or desirable. Feistel ciphers [Fei73] are a special class of iterated block ciphers where the ciphertext is calculated from the plaintext by repeated application of the same transformation or round function. It is of course possible to design iterative ciphers that are not Feistel ciphers, yet whose encryption and decryption (after a certain re-ordering or re-calculation of variables) are structurally the same. www.rsa.com /rsalabs/node.asp?id=2169   (354 words)

 Technical Details Both CipherPack and CipherPack Pro use symmetrical key block cipher algorithms as well as a lossless compression algorithm. They are suitable for all types of data and 'pack' the resultant file with the decryption and decompression code. CipherPack implements a type of iterated block cipher known as a Feistel cipher, with 64 bit blocks, a maximum key size of 120 bits and 60 rounds. www.cipherpack.com /technical.htm   (350 words)

 Feistel cipher - CryptoDox Feistel ciphers are a special class of iterated block ciphers where the ciphertext is calculated from the plaintext by repeated application of the same transformation or round function. Feistel ciphers are also sometimes called DES-like ciphers Feistel ciphers are named after IBM cryptographer Horst Feistel; it is also commonly known as a Feistel network. cryptodox.com /Feistel_cipher   (113 words)

 The Inner Structure of the Feistel Round And here is the tableau for a Feistel round, which, for this example, is two rounds of a cipher that operates on four bit values with the S-box (3,1,0,2) as the f-function. In other words, with a two-round Feistel cipher, the f-function output is always the plaintext XOR the ciphertext, and so the subkey is found by inverting the f-function, and comparing the result to the input, which is visible in the ciphertext for the second round, and visible in the plaintext for the first round. What would be of concern in connection with the general security of block ciphers would be if one could easily take two known plaintexts, and solve a four-round Feistel cipher by imposing the constraint (essentially, on the result after the second round) that both sets of equations simultaneously have the same subkeys. www.quadibloc.com /crypto/co040906.htm   (3035 words)

 RSA Laboratories - 3.6.7 What are some other block ciphers? While the cipher does not have a Feistel structure (see Question 2.1.4), decryption is carried out in the same manner as encryption once the decryption subkeys have been calculated from the encryption subkeys. The cipher structure was designed to be easily implemented in both software and hardware, and the security of IDEA relies on the use of three incompatible types of arithmetic operations on 16-bit words. It is a Feistel cipher (see Question 2.1.4) and each round consists of a key-dependent permutation and a key-and-data-dependent substitution. www.rsa.com /rsalabs/node.asp?id=2254   (1335 words)

 Re: Schneier's "Helix" cipher is remarkably similar to the "generic fe Re: Schneier's "Helix" cipher is remarkably similar to the "generic feistel cipher", David Wagner Re: Schneier's "Helix" cipher is remarkably similar to the "generic feistel cipher", John Hadstate Re: Schneier's "Helix" cipher is remarkably similar to the "generic feistel cipher", Joe Peschel www.newsfeeds.com /archive/sci-crypt/msg07241.html   (350 words)

 CS 4803 - David Pritchett [AES - Introduction] Cast-256 is a symmetric Feistel cipher that is an extension of the Cast-128 algorithm. E2 is a twelve round, symmetric Feistel cipher that encrypts in 128-bit blocks. LOKI97 is a sixteen round, 128-bit symmetric Feistel cipher that uses a complex round function that invloves S-box Substitutions, a P-box Permutation, and logical and mathematical operations. www.prism.gatech.edu /~gte043j/CS4803/3.html   (1736 words)

 DES Cipher Applet   (Site not responding. Last check: ) Note that the plaintext is first converted to ASCII codes in binary, then the bits are grouped into 12-bit blocks and encrypted with a Feistel cipher that is similar to a simplified DES. A Feistel structure is a method for constructing a block cipher (one that encrypts a fixed number of bits at a time) using an arbitrary function. In a Feistel cipher, the block is split into two halves. www.usafa.af.mil /df/dfcs/acis/applets/DESCipherApplet.html   (327 words)

 New Document   (Site not responding. Last check: ) An iterated block cipher is a block cipher involving the sequential repetition of an internal function called a round function. The f function of the Feistel cipher may be a product cipher, though f itself need not be invertible to allow inversion of the Feistel cipher. The successive rounds of a Feistel cipher operate on alternating halves of the ciphertext, while the other remains constant. aztecsarun.brinkster.net /DES.asp   (387 words)

 ...And The Winner Of The AES Competition is Rijndael! Feistel algorithms are algorithms that use Feistel constructions. It is assumed for the duration of this article that "Extended Feistel" design is an arbitrary term for Feistel design with enough modifications to warrant a distinct design class. A Feistel cipher is an iterated block cipher composed of repeated iterations of the same transformation. www.cs.rit.edu /~mds1761/cs705paper.html   (4494 words)

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