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# Topic: Block size (cryptography)

 A Variable Size Core for Block Cipher Cryptography 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. www.ciphersbyritter.com /VSBCCORE.HTM   (3874 words)

 Block size (cryptography) - Wikipedia, the free encyclopedia 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. en.wikipedia.org /wiki/Block_size_(cryptography)   (388 words)

 Encyclopedia: Block size (cryptography)   (Site not responding. Last check: 2007-10-21) In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. Category: Cryptography 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, the CS-Cipher is a block cipher invented by Jacques Stern and Serge Vaudenay in 1998. www.nationmaster.com /encyclopedia/Block-size-(cryptography)   (3000 words)

 Cryptography :: Web Articles :: Cryptography is also considered a branch of engineering, but it is considered to be an unusual one as it deals with active, intelligent and malevolent opposition (see cryptographic engineering and security engineering). In practice, the term cryptography (from the Greek kryptÃ³s, "hidden", and grÃ¡phein, "to write") is often used to refer to the field as a whole; crypto is an informal abbreviation. Asymmetric cryptography also provides mechanisms for digital signatures, which are a way to establish with high confidence (under the assumption that the relevant private key has not been compromised in any way) that the message received was sent by the claimed sender. www.webarticles.com /Computers/Computer-Science/Cryptography   (2271 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. The fixed length is called the block size, and for many block ciphers, the block size is 64 bits. 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. www.rsasecurity.com /rsalabs/node.asp?id=2168   (342 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. Modern block ciphers can be seen as a variant of this idea, in the sense that they try hide the message under a very large alphabet that depends on the key. 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)

 PEP 272 -- API for Block Encryption Algorithms v1.0   (Site not responding. Last check: 2007-10-21) Block ciphers encrypt multibyte inputs of a fixed size (frequently 8 or 16 bytes long), and can be operated in various feedback modes. For all feedback modes, the length of strings passed to the encrypt() and decrypt() must be a multiple of the block size. For algorithms with a variable block size, this value is equal to the block size selected for this object. www.python.org /peps/pep-0272.html   (1115 words)

 Cryptography | World of Computer Science Block ciphers operate on discrete blocks of data, cascading each block in turn through a series of stages, or rounds, of transpositions and substitutions. Block ciphers usually, but not always, operate on blocks of data that are the same size as the key. The DES is a block cipher that encrypts 64-bit blocks of data, one at a time using a 56-bit key over 16 stages, or rounds, of substitution and transposition. www.bookrags.com /research/cryptography-wcs   (3004 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. To decrypt, the ciphertext is broken into L and R blocks, and the key and the R block are run through the hash function to get the same hash result used in the last cycle of encryption; notice that the R block was unchanged in the last encryption cycle. www.freesoft.org /CIE/Topics/143.htm   (1497 words)

 Obviex™ - How to Calculate the Size of Encrypted Data?   (Site not responding. Last check: 2007-10-21) If the size of the original data (encrypted using a block-cipher algorithm with padding) is an exact multiple of the encryption block size, padding will increase the size of the ciphertext by one block. CipherText = PlainText + Block - (PlainText MOD Block) Before being encrypted, the first block of the plaintext data is XORed with the initialization vector and the result of the XOR operation is encrypted producing the first encrypted block. www.obviex.com /Articles/CiphertextSize.aspx   (2369 words)

 Cryptology Much of the terminology of cryptography can be linked back to the time when only written messages were being encrypted and the same terminology is still used regardless of whether it is being applied to a written message or a stream of binary code between two computers. Since different plaintext blocks are mapped to different ciphertext blocks, a block cipher effectively provides a permutation of the set of all possible messages. The number of rounds in an iterated block cipher depends on the desired security level of the encrypted ciphertext and the trade-off that must be made with performance; fairly obviously a iterated block cipher with a large number of rounds will require more processing time. www.ridex.co.uk /cryptology   (10089 words)

 [No title]   (Site not responding. Last check: 2007-10-21) A block cipher operates on a block of data (for example, multiple bytes) in a single ciphering, as opposed to a stream cipher, which operates on bytes or bits as they occur. A block cipher is a transformation between plaintext block values and ciphertext block values, and is thus an emulated simple substitution on huge block-wide values. When a codebook attack is possible on a block cipher, the complexity of the attack is controlled by the size of the block (that is, the number of elements in the codebook) and not the strength of the cipher. www.techsupport.i-p.com /cryptography.html   (13399 words)

 Cryptography in Microsoft.NET Part I: Encryption   (Site not responding. Last check: 2007-10-21) Cryptography algorithms (ciphers) are mathematical functions used for encryption and decryptions. Since Block ciphers working on CBC modes XOR each block with the previous encrypted block, the first block of the message needs a byte array, of same block size, with which it will be XORed This byte array is called IV or Initialization Vector. Often last block of the message will be smaller that the expected block size in which case a predetermined string will be repeatedly added to the end of the block to make it to the expected size. www.c-sharpcorner.com /Code/2002/Dec/CryptEncryption.asp   (1721 words)

 The Laws of Cryptography: Conventional Block Ciphers   (Site not responding. Last check: 2007-10-21) Block ciphers take a block of plaintext, whose size depends on the cryptosystem, and use a fixed key of some block length also depending on the cryptosystem, to produce a block of ciphertext, usually the same length as the block of plaintext. In cryptography, a random code with no duplicate code words could be considered for a cryptographic code, but the code table would need to be unacceptably large, and the decoding algorithm would be difficult to make efficient. Each ciphertext block depends on the current plaintext and on all plaintext that came before: If a single bit of the initialization vector of of the first plaintext block is changed, then all ciphertext blocks will be randomly altered (50% of bits different from what they were on the average). www.cs.utsa.edu /~wagner/laws/blockcipher.html   (1974 words)

 Cryptography : Basic techniques, Crypto System - Ankit If the message is too long to fit in a single block, the message will be broken in to as many blocks as necessary. Decryption is performed by applying the reverse procedure to the cipher text block, whilst using the same secret key. The fixed length is called the block size, and for many block ciphers, the block size is 64 bits. www.ankitjain.info /articles/Cryptography_ankit3.htm   (726 words)

 B-Con: Links: Cryptography   (Site not responding. Last check: 2007-10-21) Cryptography is a huge subject to study, to aid those seeking to learn the basics of it, I have compiled a list of links, organized by subject. If the entire idea of cryptography really interests you think you may be interested in a career in it, read Schneier's article on pursuing a crytography-related career, and you might want to look into the NSA. Blowfish -- No effective attacks have been found against it, but its block size is smaller than prefered, so more attention is being given to AES and the like. b-con.us /security/intro_cryptography.php   (653 words)

 Python Cryptography Toolkit The message block's serial number is placed on the chaff block and all the packet's chaff blocks are randomly interspersed with the single wheat block. Chaffed blocks will contain multiple instances of 3-tuples with the same serial number, but the only way to figure out which blocks are wheat and which are chaff is to perform the MAC hash and compare values. After the random block is generated, the magic string, length of the original file, and original filename are all encrypted before the file data is finally processed. www.amk.ca /python/writing/pycrypt   (7734 words)

 Cryptography Technology The standard code implements block sizes of 16, 24 and 32 bytes, fixed during compilation, and a variable block size option covering these block sizes chosen at time of use. The block and key sizes are specified in units of bytes to match the associated input arrays (legal values 16, 24 and 32). For the variable block size version there is a call to set the block size, a value of 16 being assumed if this is not set (i.e. fp.gladman.plus.com /cryptography_technology/rijndael/index.htm   (1735 words)

 Block size (cryptography) - InfoSearchPoint.com   (Site not responding. Last check: 2007-10-21) Both the input (plaintext) and output (ciphertext) are the same length; this is more-or-less required by the Pigeonhole principle, and the fact that the cipher must be invertible. Thus even when used with a proper encryption mode, only $2^\left\{32\right\} \times 8$ B = 32 GB of data can be safely sent under one key. A few block ciphers, such as RC5, actually support a variable block size, while Joan Daemen's 3-Way has a 96 bit block. www.infosearchpoint.com /display/Block_size_(cryptography)   (336 words)

 RSA Laboratories - 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. A more general version of the standard [ISO92b] generalized the four modes of DES to be applicable to a block cipher of any block size. www.rsa.com /rsalabs/node.asp?id=2168   (321 words)

 What are block and stream ciphers? DES is a block cipher with a 64 bit block size. AES is a block cipher with a 128 bit block size. RSA and Diffie-Hellman are block ciphers with variable block sizes. www.tech-faq.com /block-stream-cipher.shtml   (160 words)

 Cryptography in the Database: The Last Line of Defense Block ciphers encrypt a chunk of several bits all at once, while stream ciphers generally encrypt one bit at a time as the data stream flows past. When a block cipher must encrypt data longer than the block size, the data is first broken into blocks of the appropriate size, and then the encryption algorithm is applied to each. Given that block ciphers operate on a fixed block size, any blocks of data smaller than that size must be padded. www.securityfocus.com /excerpts/20/2   (1383 words)

 biology - GOST In cryptography, GOST (Russian ГОСТ) (GOsudarstvennyi STandard, Russian for "Government Standard") is a symmetric key block cipher published in 1990 as the Soviet standard (GOST 28147-89). It is the Soviet equivalent of the United States standard algorithm, DES, and is similar in structure. GOST has a 64-bit block size and a key length of 256 bits. www.biologydaily.com /biology/GOST   (436 words)

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