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# Topic: Block cipher modes of operation

###### In the News (Thu 18 Apr 19)

 Block Cipher Modes of operation In CBC mode, the input message is once again divided into blocks and each block is XORed to the previous ciphertext block (the output of the previous encrytion) before being encrypted. CBC is the most commonly used mode of operation but its main drawback is that the message must be padded to a multiple of the cipher block size, and therefor is being replaced by synchronous stream-ciphers such as CFB or OFB. If at a later stage, you have several block ciphers implemented, you could change this prototype to have a pointer to a block cipher, which would then be used internally by the mode of operation. www.progressive-coding.com /tutorial.php?id=3   (1419 words)

 Kids.Net.Au - Encyclopedia > Block cipher A block cipher is a mathematical function, typically implemented in modern times by a computer program function, that takes two inputs and produces one output. A few are: RC5, Safer block cipher[?] (and its successors to be discussed in that article), IDEA, Blowfish, and also the losing AES finalists: Twofish, Serpent[?], RC6, and Mars[?]. It is occasionally practical to use a block cipher to encrypt a message exactly the same size at the plaintext block. www.kids.net.au /encyclopedia-wiki/bl/Block_cipher   (517 words)

 Block cipher modes of operation - Biocrawler   (Site not responding. Last check: ) In cryptography, a block cipher operates on blocks of fixed length, often 64 or 128 bits. The disadvantage of this method is that identical plaintext blocks are encrypted to identical ciphertext blocks; it does not hide data patterns. Because a block cipher works on units of a fixed size, but messages come in a variety of lengths, some modes (mainly CBC) require that the final block be padded before encryption. www.biocrawler.com /encyclopedia/Block_cipher_modes_of_operation   (990 words)

 Advanced Encryption Standard As the new block cipher 'standard' it is currently being deployed on a large scale. The most common way to attack block ciphers is to try various attacks on versions of the cipher with a reduced number of rounds. Along with the cipher itself, a document concerning "modes of operation" is also expected to be made an official standard. www.ebroadcast.com.au /lookup/encyclopedia/ae/AES.html   (679 words)

 Encryption software modes 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. In CFB mode the previous ciphertext block is encrypted and the output produced is combined with the plaintext block using exclusive-OR to produce the current ciphertext block. CFB mode is as secure as the underlying cipher and plaintext patterns are concealed in the ciphertext by the use of the exclusive-or operation. crypto-systems.com /modes.html   (611 words)

 FineCrypt - Encryption Software In CFB mode the previous ciphertext block is encrypted and the output produced is combined with the plaintext block using exclusive-OR to produce the current ciphertext block. CFB mode is as secure as the underlying cipher and plaintext patterns are concealed in the ciphertext by the use of the exclusive-or operation. With CFB mode and full feedback, when two ciphertext blocks are identical, the outputs from the block cipher operation at the next step are also identical. www.finecrypt.net /modes.html   (601 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.com /support/cryptography/algorithms/symmetric.html   (3707 words)

 Basic Block Cipher Modes Since each ciphertext block was a function of the plaintext block and the previous ciphertext block, each plaintext block is a function of the ciphertext block and the previous ciphertext block. In this decipherment example, the first plaintext block is totally garbled, because the erroneous ciphertext block is the input into the block cipher; the second plaintext block only has an error which matches that of the plaintext block, because the erroneous block is used in a Vigenere calculation after the block cipher. This mode was not included among the modes originally recommended for use with DES, but it is included among the basic modes of operation recommended for use with the new AES standard. www.quadibloc.com /crypto/co040601.htm   (1554 words)

 PEP 272 -- API for Block Encryption Algorithms v1.0 Block ciphers encrypt multibyte inputs of a fixed size (frequently 8 or 16 bytes long), and can be operated in various feedback modes. This mode isn't considered important enough to make it worth requiring it for all block encryption ciphers, though supporting it is a nice extra feature.) In a strict formal sense, stream ciphers encrypt data bit-by-bit; practically, stream ciphers work on a character-by-character basis. For all feedback modes, the length of strings passed to the encrypt() and decrypt() must be a multiple of the block size. www.python.org /dev/peps/pep-0272   (1115 words)

 FIPS 81 - Des Modes of Operation 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). 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. The CFB mode is a stream method of encryption in which the DES is used to generate pseudorandom bits which are exclusive-ORed with binary plain text to form cipher text. www.itl.nist.gov /fipspubs/fip81.htm   (6653 words)

 OpenSSL: Documents, des_modes(7) The CBC mode produces the same ciphertext whenever the same plaintext is encrypted using the same key and starting variable. The CFB mode produces the same ciphertext whenever the same plaintext is encrypted using the same key and starting variable. The chaining operation makes the ciphertext variables dependent on the current and all preceding variables and therefore j-bit variables are chained together and can not be rearranged. www.openssl.org /docs/crypto/des_modes.html   (801 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)

 TrueCrypt - Free Open-Source Disk Encryption Software - Documentation - Modes of Operation CBC mode has been deprecated (however, volumes encrypted in CBC mode can still be mounted by the current version of TrueCrypt). Ciphers in a cascade use mutually independent keys (note that the header keys they use are independent as well, even though they are derived from a single password – see the section Header Key Derivation, Salt, and Iteration Count). AES operating in LRW mode is also referred to as LRW-AES. www.truecrypt.org /docs/modes-of-operation.php   (179 words)

 [No title] Cipher Block Chaining Mode A. Show F 2.7(a) B. Introduction to CBC mode 1. The input to the encryption algorithm(DES) is the XOR of the current plaintext block and the preceding ciphertext block. One desirable property of a stream cipher is that the ciphertext be of the same length as the plaintext. webspace.ship.edu /jcthom/schedule/csc432/StallingsNotes/ConvEncrMessConfid2/CphBlkMdsOp2.3.html   (869 words)

 rehpic Block cipher is a type of symmetric cipher (although some assymetric use the same concept) which is applied on group of bits. Many block ciphers can be categorised as Feistel ciphers (A feistel network is a specific way of operating functions). This mode is the most simple and one of the first applied to block ciphers. www.cipher.org.uk /index.php?p=course/Block_Cipher_modes.course   (261 words)

 Definition of Block cipher modes of operation   (Site not responding. Last check: ) In cryptography, a block cipher operates on blocks of fixed length, often 64 or 128 bits. The disadvantage of this method is that identical plaintext blocks are encrypted to identical ciphertext blocks; it does not hide data patterns. Because a block cipher works on units of a fixed size, but messages come in a variety of lengths, some modes (mainly CBC) require that the final block be padded before encryption. www.wordiq.com /definition/Block_cipher_modes_of_operation   (1054 words)

 NIST Computer Security DRAFT Publications   (Site not responding. Last check: ) GCM, submitted to NIST by David McGrew and John Viega, combines a variation of the Counter Mode for encryption with an authentication mechanism that is based on a universal hash function. The underlying (approved) block cipher must have a block size of 128 bits (i.e., the AES algorithm) and the size of the authentication tag is 96-128 bits. Further information on the development of block cipher modes of operation is available at the modes home page, http://nist.gov/modes. csrc.nist.gov /publications/drafts.html   (2373 words)

 Block cipher modes   (Site not responding. Last check: ) Block ciphers operates on blocks of plain-text and cipher-text. Operating on blocks of 64 bits (8 bytes) is not always useful, and may be vulnerable to simple cryptanalysis attacks. Several block cipher ``modes of operation'' are in use today. www.pvv.ntnu.no /~asgaut/crypto/thesis/node13.html   (62 words)

 RFC 4312 (rfc4312) - The Camellia Cipher Algorithm and Its Use With IPsec This document specifies the use of the Camellia cipher in CBC mode within ESP. This mode requires an Initialization Vector (IV) size that is the same as the block size. Use of a randomly generated IV prevents generation of identical cipher text from packets that have identical data spanning the first block of the cipher algorithm's block size. The cipher's encryption and decryption key is taken from the first 128, 192, or 256 bits of the keying material. www.faqs.org /rfcs/rfc4312.html   (1631 words)

 Print the story   (Site not responding. Last check: ) The main component of CMAC is a block cipher. Recommendation for Block Cipher Modes of Operation: The CMAC Mode for Authentication (NIST Special Publication 800-38B) is available at http://csrc.nist.gov/publications/nistpubs/index.html#sp800-38B. It is the third of a series of publications recommending modes of operation to provide confidentiality or authentication for digital data. www.physorg.com /printnews.php?newsid=4381   (268 words)

 Block Cipher and Its Modes - Associated Content In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. Operation is very similar; in particular, CFB decryption is almost identical to CBC decryption performed in reverse. CTR mode has similar characteristics to OFB, but also allows a random access property during decryption, and is believed to be as secure as the block cipher being used. www.associatedcontent.com /article/108416/block_cipher_and_its_modes.html   (463 words)

 [No title]   (Site not responding. Last check: ) For example, some block cipher algorithms are capable of operating with more than one block size and/or accepting more than one key size --e.g. For example, the block cipher Output Feedback (OFB) mode of operation is described in the literature ([HAC], chapter 7) as commonly used in one of two ways: per ISO 10116, and per FIPS 81. Modes of operation, always operate on an underlying block cipher to produce their output. www.ietf.org /proceedings/03mar/I-D/draft-naffah-naming-00.txt   (2740 words)

 [saag] Announcement of NIST Modes Recommendation (fwd)   (Site not responding. Last check: ) Five confidentiality modes are specified for use with any FIPS-approved block cipher, such as the AES. NIST also expects to publish a 2002 edition of SP 800-38A in which the domain of the CBC mode is extended (to include plaintexts whose bit lengths are not a multiple of the block size); all of the technical material that is specified in the 2001 edition is expected to remain valid. Modes development is expected be an ongoing effort; later parts of the series may be devoted to the specification of new modes. mailman.mit.edu /pipermail/saag/2001q4/000362.html   (225 words)

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