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Topic: Cipher Block Chaining

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Block cipher

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	Block Ciphers
		CBC is the most commonly used mode of operation for a block cipher.
		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)

	Protecting Message Integrity (Site not responding. Last check: 2007-10-13)
		Subjecting the previous block cipher output to a one-bit rotation in addition to switching from addition to subtraction, although fairly trivial, would seem to remove any relationship between the new value to be applied to the current block and the previous ciphertext which would be trivial enough to be useful.
		The XOR sum of all the blocks of the plaintext is encrypted using almost the same pattern, except that the addition of n+1 times the random block to the block cipher output is omitted, to produce block n+1 of the ciphertext.
		Since the length of the plaintext block and the length of the ciphertext block are equal, the plaintext of the last block is determined on decipherment by repeating the encipherment calculation, and then XORing the AES output with the last ciphertext block.
	www.quadibloc.com /crypto/co040603.htm (3745 words)

	Crypt::CBC
		First it needs the name of the block cipher algorithm that will encrypt or decrypt the data in blocks of fixed length known as the cipher's "blocksize." Second, it needs an encryption/decryption key to pass to the block cipher.
		These read-only methods return the identity of the chosen block cipher algorithm, padding method, key and block size of the chosen block cipher, and whether PCBC chaining is in effect.
		where $block is the current block of data, $blocksize is the size to pad it to, $direction is "e" for encrypting and "d" for decrypting, and $padded_block is the result after padding or depadding.
	cpan.uwinnipeg.ca /htdocs/Crypt-CBC/Crypt/CBC.html (2435 words)

	RSA Security - 2.1.4.3 What is Cipher Block Chaining Mode?
		CBC mode is as secure as the underlying block cipher against standard attacks.
		The speed of encryption is identical to that of the block cipher, but the encryption process cannot be easily parallelized, although the decryption process can be.
		PCBC (Propagating Cipher Block Chaining) mode is a variation on the CBC mode of operation and is designed to extend or propagate a single bit error in the ciphertext.
	www.rsasecurity.com /rsalabs/node.asp?id=2171 (344 words)

	FIPS 81 - Des Modes of Operation
		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.
		CBC is a block cipher system in which the first plain text data block is exclusive-ORed with a block of pseudo-random data prior to being processed through the DES.
	www.itl.nist.gov /div897/pubs/fip81.htm (6653 words)

	SecureTask - Encryption Freeware
		This means any blocks of plaintext that are identical and are either in the same message, or in a different message that is encrypted with the same key, will be transformed into identical ciphertext blocks.
		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.
	www.securetask.net /modes.html (601 words)

	Basic Block Cipher Modes (Site not responding. Last check: 2007-10-13)
		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.
		In this decipherment example, the first plaintext block only has an error which matches that of the plaintext block, but the second block is totally garbled, because the erroneous ciphertext block went through the block cipher before being applied to the plaintext.
	www.quadibloc.com /crypto/co040601.htm (1554 words)

	A Variable Size Core for Block Cipher Cryptography (Site not responding. Last check: 2007-10-13)
		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.
		Small block ciphers prevent codebook attacks by randomizing the plaintext (often with Cipher Block Chaining) so that the plaintext block values are distributed evenly across all possible block values.
	www.ciphersbyritter.com /VSBCCORE.HTM (3874 words)

	SecurityDocs: Comment on An Introduction to Block Cipher Algorithms and Their Applications in Communication Security
		Cipher Feedback is similar to Cipher Block Chaining, but instead of encrypting the XORed block, it starts by encrypting the seeded value, and then XORing that with the first block.
		Block Cipher algorithms are subject to the same attacks that Symmetric Key algorithms are.
		Block Cipher algorithms also have the advantage that it isn’t difficult to encrypt and decrypt messages, because the same key is used to encrypt and decrypt.
	www.securitydocs.com /library/3259 (1345 words)

	CBC - Cipher Block Chaining
		Data from this survey is used to generate the CBC maps.
		Determines whether the proper number of red blood cells, white blood cells and platelets are present in the patient's blood.
		CBC is the test that indicates the amount of red blood cells, white blood cells and platelets that are in the body.
	www.auditmypc.com /acronym/CBC.asp (306 words)

	Kryptographie FAQ: Frage 84: What are the Counter and PCBC Modes?
		Instead of deriving one data block as the encryption of the previous data block, Diffie proposed encrypting the quantity i + IV (mod 264) for the ith data block, where IV is some initialization vector.
		The Propagating Cipher Block Chaining (PCBC) mode of encryption is another mode of operation using block ciphers.
		The PCBC mode is a variation on the CBC mode of operation and is designed to extend or propagate a single bit error in the ciphertext.
	www.iks-jena.de /mitarb/lutz/security/cryptfaq/q84.html (180 words)

	The ESP CBC-Mode Cipher Algorithms
		While this document illustrates certain cipher algorithms such as Blowfish [Schneier93], CAST-128 [1], 3DES, IDEA [10][12], and RC5 [3], any other block cipher algorithm may be used with ESP if all of the variables described within this document are clearly defined.
		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.
		The cipher's encryption and decryption key is taken from the first bits of the keying material, where represents the required key size.
	xml.resource.org /public/rfc/html/rfc2451.html (2285 words)

	Cipher (GNU Classpath 0.93 Documentation)
		where algorithm is the base name of a cryptographic cipher (such as "AES"), mode is the abbreviated name of a block cipher mode (such as "CBC" for cipher block chaining mode), and padding is the name of a padding scheme (such as "PKCS5Padding").
		Finally, when requesting a block cipher in stream cipher mode (such as AES in OFB or CFB mode) the number of bits to be processed at a time may be specified by appending it to the name of the mode; e.g.
		Initialize this cipher with the public key from the given certificate and the specified source of randomness.
	developer.classpath.org /doc/javax/crypto/Cipher.html (3270 words)

	[No title]
		Abstract This document describes the use of the DES Cipher algorithm in Cipher Block Chaining Mode, with an explicit IV, as a confidentiality mechanism within the context of the IPSec Encapsulating Security Payload (ESP).
		Introduction This document describes the use of the DES Cipher algorithm in Cipher Block Chaining Mode as a confidentiality mechanism within the context of the Encapsulating Security Payload.
		In CBC mode, the "effective plaintext" for an encryption is the XOR of the actual plaintext and the ciphertext of the preceeding block.
	ietf.org /rfc/rfc2405.txt (2271 words)

	Cipher block chaining (Site not responding. Last check: 2007-10-13)
		Cipher Block Chaining (CBC) uses feedback to feed the result of encryption back into the encryption of the next block.
		The subsequent block will have bit errors at the same positions as the original erroneous block.
		A system that uses CBC must therefore ensure that the block structure remains intact.
	www.pvv.ntnu.no /~asgaut/crypto/thesis/node15.html (232 words)

	FIPS PUB 81 -- DES MODES OF OPERATION (Site not responding. Last check: 2007-10-13)
		INITIALIZATION VECTOR (IV): A binary vector used in the initial input block in the CFB and OFB modes and as the randomizing block that is exclusive-ORed with the first data block in the CBC mode.
		The resulting output block, which equals the original input block to the DES during encryption, is exclusive-ORed with the IV (must be same as that used during encryption) to produce the first plain text block, i.e., (D1,D2,...,D64)= (O1ÅIV1,O2ÅIV2,...,O64ÅIV64).
		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) = (O1ÅC1,02ÅC2,...,064ÅC64).
	www.columbia.edu /~ariel/ssleay/fip81/fip81.html (6910 words)

	Cipher 2.2 Information
		Cipher is a small application to keep your secrets really secret by enciphering them with one of the most reliable encryption algorithms.
		The program uses the IDEA block cipher encryption algorithm which is patented by Mediacrypt.
		The block cipher is being used with cipher block chaining (with zero initialization).
	www.klawitter.de /palm/cipher.html (1420 words)

	Bellare - CBC (Site not responding. Last check: 2007-10-13)
		where f is some underlying block cipher (e.g., the Data Encryption Standard) and a is its key.
		We provide its first formal justification, showing the following general lemma: that cipher block chaining a pseudorandom function gives a pseudorandom function.
		Underlying our results is a technical lemma of independent interest, bounding the success probability of a computationally unbounded adversary in distinguishing between a random ml-bit to l-bit function and the CBC MAC of a random l-bit to l-bit function.
	www-cse.ucsd.edu /users/mihir/papers/cbc.html (160 words)

	What is cipher block chaining? - a definition from Whatis.com - 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).
		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.
		Basically, in cipher block chaining, each plaintext block is XORed (see XOR) with the immediately previous ciphertext block, and then encrypted.
	searchsecurity.techtarget.com /sDefinition/0,,sid14_gci344945,00.html (470 words)

	BBC - h2g2 - Block-Chaining Ciphers
		A block-chaining, or feedback, cipher is a type of block cipher in which some portion of the previous encryption block is used to modify the current encryption block.
		Generally polyalphabetic ciphers are more secure than monoalphabetic ciphers and generally longer blocklengths are more secure than shorter blocklengths so to combine a large block with a huge potential range of alphabets should provide a truly difficult challenge for a cryptanalyst.
		It is a 128bit cipher with a 256bit keyspace, where DES was only 64bit with a 56bit keyspace and it resists types of theoretical attack not even discovered when DES was selected.
	www.bbc.co.uk /dna/h2g2/A611272 (340 words)

	Block cipher modes of operation - Wikipedia, the free encyclopedia
		CBC has been the most commonly used mode of operation.
		However, because the plaintext or ciphertext is only used for the final XOR, the block cipher operations may be performed in advance, allowing the final step to be performed in parallel once the plaintext or ciphertext is available.
		They are generally used in modes of operation similar to the block modes described here.
	en.wikipedia.org /wiki/Block_cipher_modes_of_operation (1970 words)

	Cipher feedback mode (Site not responding. Last check: 2007-10-13)
		In the Cipher Feedback Mode (CFB) is data encrypted in units smaller than the block size.
		Figure 2.6 shows how single bytes can be encrypted and decrypted using a block cipher in CFB mode.
		This cipher block will then be fed to the shift register and cause bit errors in the plain text for as long as the erroneous bits stay in the shift register.
	www.pvv.ntnu.no /~asgaut/crypto/thesis/node16.html (342 words)

	Crypt-BabyRijin-0.70
		For CBC mode, the IV (initial vector) can be changed by a fucntion call suited for the purpose.
		In this implementation, it adds on an extra block to the end of the message, is the size of the message, and the continues with the hashing operation.
		Encrypts the $input block (string) using the $key block using the current set mode ECB or CBC.
	www.public.iastate.edu /~ironstar/portfolio/docs/crypt-babyrijin.html (903 words)

	Java Program 1 for Triple DES Encryption with Cipher Block Chaining, by J. Orlin Grabbe (Site not responding. Last check: 2007-10-13)
		The program here uses CBC mode (Cipher Block Chaining mode) to encrypt the data.
		This block is encrypted first; then the encrypted block is XOR'd with the next plain text block (the first 8 bytes of the target file to be encrypted) before it is encrypted.
		The result of that encryption is then X0R'd with the next plain text block (the second 8 bytes of the target file) before that block is encrypted.
	www.orlingrabbe.com /3des1_cbc.htm (440 words)

	[No title]
		The Data Encryption Standard Algorithm is a block cipher that enciphers identical eight-byte plaintext blocks into identical eight-byte ciphertext blocks.
		Repetitions of some other blocks may also be visible; for example, telephone numbers in the plain text when aligned with the eight-byte DES blocks, can be recognized as identical in the ciphertext.
		By using Mutation's Cipher Block Chaining option it is possible to use DES in such a manner that identical eight-byte plaintext blocks virtually always yield different ciphertext blocks, without altering the security of the existing algorithm.
	www.textfiles.com /computers/DOCUMENTATION/mutation.txt (2721 words)

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