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Topic: Block cipher


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  Block cipher - Wikipedia, the free encyclopedia
In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation.
Block ciphers can be contrasted with stream ciphers; a stream cipher operates on individual digits one at a time, and the transformation varies during the encryption.
An early and highly influential block cipher design was the Data Encryption Standard (DES), developed at IBM and published as a standard in 1977.
en.wikipedia.org /wiki/Block_cipher   (1058 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.
The disadvantage of CBC is that the encryption of a data block becomes dependent on all the blocks prior to it.
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).
www.freesoft.org /CIE/Topics/143.htm   (1497 words)

  
 SSH : Support : Cryptography A-Z : Algorithms : Secret Key Cryptosystems
Block ciphers: A block of cipher transforms n-bit plaintext blocks to n-bit ciphertext blocks under the influence of a cipher key k.
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.
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   (3577 words)

  
 cipher block chaining - a Whatis.com definition - see also: CBC
Cipher block chaining (CBC) is a mode of operation for a block cipher (one in which a sequence of bits are encrypted as a single unit or block with a cipher key applied to the entire block).
Cipher block chaining uses what is known as an initialization vector (IV) of a certain length.
One of its key characteristics is that it uses a chaining mechanism that causes the decryption of a block of ciphertext to depend on all the preceding ciphertext blocks.
searchsecurity.techtarget.com /sDefinition/0,,sid14_gci344945,00.html   (336 words)

  
 How Security is Implemented
Block ciphers use a specified sized key on a specified sized block of plaintext to generate a specified sized block of ciphertext.
Each plaintext block is exclusive-ored with the ciphertext of the previous block (or IV for the first block) then encrypted with the key, thus making paralellization difficult for piped plaintext.
Feistel Ciphers are a special case of iterated block ciphers in which the plaintext is halved.
www.mis2.udel.edu /~hector/telecomm/ciphers.html   (1400 words)

  
 A Variable Size Core for Block Cipher Cryptography
The first known publication of the concept of a Variable Size Block Cipher (VSBC) -- and the first published VSBC design -- was the 1995 Aug 20 sci.crypt announcement by Ritter and the resulting discussion.
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.
www.ciphersbyritter.com /VSBCCORE.HTM   (3874 words)

  
 Ritter's Crypto Glossary and Dictionary of Technical Cryptography
When used with a conventional block cipher, an AONT appears to increase the cost of a brute-force attack by a factor which is the number of blocks in the message.
Typically, a form of stream cipher where the ciphertext output is fed back to modify the state of the random number generator producing the running key or confusion sequence.
The observed property of a block cipher constructed in layers or "rounds" with respect to a tiny change in the input.
www.ciphersbyritter.com /GLOSSARY.HTM   (9299 words)

  
 RSA Security - 2.1.4 What is a block cipher?
A block cipher is a type of symmetric-key encryption algorithm that transforms a fixed-length block of plaintext (unencrypted text) data into a block of ciphertext (encrypted text) data of the same length.
For those with a mathematical background (see Appendix A): Since different plaintext blocks are mapped to different ciphertext blocks (to allow unique decryption), a block cipher effectively provides a permutation (one to one reversible correspondence) of the set of all possible messages.
When we use a block cipher to encrypt a message of arbitrary length, we use techniques known as modes of operation for the block cipher.
www.rsasecurity.com /rsalabs/node.asp?id=2168   (342 words)

  
 FIPS 81 - Des Modes of Operation   (Site not responding. Last check: 2007-10-21)
The second cipher text block is then used as the input block and is processed through the DES in the decrypt state and the resulting output block is exclusive-ORed with the first cipher text block to produce the second plain text data block, i.e., (D1,D2,...,D64) = (O1 C1,02 C2,...,064 C64).
Cipher text representing a partial data block must be decrypted in a manner as specified for the application.
In a block method, the DES input block is (or is a simple function of) the plain text to be encrypted and the DES output block is the cipher text.
www.itl.nist.gov /fipspubs/fip81.htm   (6653 words)

  
 New Page 3
Rijndael can operate over a variable-length block using variable-length keys; the version 2 specification submitted to NIST describes use of a 128-, 192-, or 256-bit key to encrypt data blocks that are 128, 192, or 256 bits long; note that all nine combinations of key length and block length are possible.
Rijndael is an iterated block cipher, meaning that the initial input block and cipher key undergoes multiple rounds of transformation before producing the output.
For ease of description, the block and cipher key are often represented as an array of columns where each array has 4 rows and each column represents a single byte (8 bits).
home.twcny.rr.com /vbgods/AESbottom_about.htm   (1367 words)

  
 ciphergoth.org: Mercy: A fast large block cipher for disk sector encryption   (Site not responding. Last check: 2007-10-21)
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.
Cryptanalysis of the Mercy block cipher, Scott Fluhrer, FSE 2001.
www.ciphergoth.org /crypto/mercy   (413 words)

  
 Programming with GNU Crypto 2.0.0   (Site not responding. Last check: 2007-10-21)
Cipher modes operate on the next level up from the underlying block cipher.
Or "ECB" mode, is the most obvious cipher mode: the cipher block is the direct output of the forward function, and the plain block is the direct output of the inverse function.
Like the other stream modes, the input block i is transformed by the exclusive-or of the block with X_i.
www.gnu.org /software/gnu-crypto/manual/Modes.html   (419 words)

  
 Cipher (Java 2 Platform SE 5.0)
The returned parameters may be the same that were used to initialize this cipher, or may contain a combination of default and random parameter values used by the underlying cipher implementation if this cipher requires algorithm parameters but was not initialized with any.
- if this cipher is a block cipher, no padding has been requested (only in encryption mode), and the total input length of the data processed by this cipher is not a multiple of block size; or if this encryption algorithm is unable to process the input data provided.
- if this cipher is a block cipher, no padding has been requested, and the length of the encoding of the key to be wrapped is not a multiple of the block size.
java.sun.com /j2se/1.5.0/docs/api/javax/crypto/Cipher.html   (5917 words)

  
 The Khazad Block Cipher
As such, it operates on data blocks of length 64 bits, and uses keys of length 128 bits.
The S-box and the diffusion matrix were chosen in a way which guarantees that encryption and decryption are the same operation except in the round subkeys.
The rationale for this is that a considerable safety margin is taken with respect to all known attacks.
paginas.terra.com.br /informatica/paulobarreto/KhazadPage.html   (529 words)

  
 [No title]
Use of a randomly generated IV prevents generation of identical ciphertext from packets which have identical data that spans the first block of the cipher algorithm's blocksize.
Some cipher algorithms have weak keys or keys that MUST not be used due to their weak nature.
Common practice is to use random data for the first IV and the last block of encrypted data from an encryption process as the IV for the next encryption process.
www.ietf.org /rfc/rfc2451.txt   (2413 words)

  
 C [Security]
A block cipher method that encrypts the base data with a block cipher and then uses the last encrypted block as the hash value.
For example, if the block size is 64 bits with eight bits processed at a time, then the shift register would be divided into eight sections.
A block cipher mode (each block is encrypted individually) that can be specified by using the CryptSetKeyParam function.
msdn.microsoft.com /library/en-us/secgloss/security/c_gly.asp   (2000 words)

  
 The MARS cipher
The MARS cipher - IBM submission to AES
MARS is a shared-key (symmetric) block cipher, supporting 128-bit blocks and variable key size.
It is designed to take advantage of the powerful operations supported in today's computers, resulting in a much improved security/performance tradeoff over existing ciphers.
www.research.ibm.com /security/mars.html   (342 words)

  
 Standard Cryptographic Algorithm Naming
Ciphers that have different key schedules, but are otherwise identical are given different names (for example, SAFER-K and SAFER-SK).
The name of such a cipher is derived by adding "-Direct" to the standard name (except that if part of the name already specifies the key schedule, that part is dropped).
BMGL is an alias for "Rijndael-256/KFB(40)"; that is, Rijndael with a 256-bit block size, used in KFB mode, with 40 bits of keystream taken for each application of Rijndael.
www.users.zetnet.co.uk /hopwood/crypto/scan/cs.html   (6436 words)

  
 NetAction's Guide to Encryption (whole guide, no reviews)
A Block Cipher is a method for encrypting data in chunks (several or many contiguous bits) as opposed to encoding bit-by-bit like a stream cipher.
A Stream Cipher is a method of encrypting data bit-by-bit, as opposed to encoding a contiguous chunk of data all at once like a block cipher.
AES is the block cipher being developed as a successor to DES.
www.netaction.org /encrypt/guide.html   (8187 words)

  
 Cryptographic Algorithms: Block and Stream Ciphers, Hash Algorithms. Kremlin Encrypt Security Software: Encrypt and ...
The block size is generally dependent on the word size of the machine the particular version of RC5 was designed to run on; on 32-bit processors (with 32-bit words), RC5 generally has a 64-bit block size.
While bitslicing is generally used to encrypt multiple blocks in parallel, the designers of Serpent have embraced the technique of bitslicing and incorporated it into the design of the algorithm itself.
SQUARE is an iterated block cipher that uses a 128-bit key length and a 128-bit block length.
kremlinencrypt.com /crypto/algorithms.html   (3164 words)

  
 Crypt::Loki97 - Crypt::CBC compliant block cipher
Loki97 is 128-bit block cipher that accepts a variable-length key.
Returns the size (in bytes) of the block (16, in this case).
This library is free software; you can redistribute it and/or modify it under the same terms as the GNU General Public License.
cpan.uwinnipeg.ca /htdocs/Crypt-Loki97/Crypt/Loki97.html   (317 words)

  
 block cipher - a Whatis.com definition
text (to produce ciphertext) in which a cryptographic key and algorithm are applied to a block of data (for example, 64 contiguous bits) at once as a group rather than to one bit at a time.
So that identical blocks of text do not get encrypted the same way in a message (which might make it easier to decipher the ciphertext), it is common to apply the ciphertext from the previous encrypted block to the next block in a sequence.
This ensures that all subsequent blocks result in ciphertext that doesn't match that of the first encrypting.
searchsecurity.techtarget.com /sDefinition/0,,sid14_gci213594,00.html   (207 words)

  
 ABC-Dir: Cipher
Warlock is a stream cipher that uses a key as long or longer then the plain text, where the key...
HC-256 is a stream cipher developed by Hongjun Wu at the Institute for Infocomm Research in Singapore.
SC128 is a new block cipher whose design is quite original.
www.abc-directory.com /view/cipher   (259 words)

  
 Hash Functions and Block Ciphers
A block cipher is a reversible function g:KxB->C, which maps a key in K and a block in B into a block in C. Usually B and C are the same set, so the block cipher permutes B in a key-specific way.
I also wrote code to find characteristics in block ciphers, choose magic constants, and test for bias in supposedly random sequences.
Go here to see how to add a key to a pseudorandom permutation, making it a block cipher.
burtleburtle.net /bob/hash   (1349 words)

  
 SecuriTeam™ - The CS^2 Block Cipher
This paper describes a new CS block cipher that is an extension of the original CS-Cipher.
The CS-Cipher is a 64-bit block cipher designed for efficiency on 8-bit processors as well as in hardware.
In this paper the CS-Cipher is extended using the results of [5] and [7] to produce an efficient 128-bit block cipher with a 128-bit secret key.
www.securiteam.com /securityreviews/5IP0515FFE.html   (304 words)

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