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Topic: Checksum

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Redundancy check

Cksum

Cyclic redundancy check

Data corruption

Cryptographic hash function

Vertical redundancy check

Longitudinal redundancy check

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Parity bit

MD4

List of checksum algorithms

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	Distributed Checksum Clearinghouse
		The Distributed Checksum Clearinghouse source carries a license that is free only to organizations that do not sell filtering devices or services except to their own users and that participate in the global DCC network.
		A DCC client reports the checksums for a mail message to a server and is told the total number of recipients of mail with each checksum.
		Because simplistic checksums of spam would not be effective, the main DCC checksums are fuzzy and ignore aspects of messages.
	www.rhyolite.com /anti-spam/dcc (2001 words)

	Checksum - Wikipedia, the free encyclopedia
		The term "checksum" is sometimes used in a more general sense to refer to any kind of redundancy check.
		Checksums on decimal numbers are discussed under check digit.
		A checksum is a form of redundancy check, a very simple measure for protecting the integrity of data by detecting errors in data that is sent through space (telecommunications) or time (storage).
	en.wikipedia.org /wiki/Checksum (347 words)

	Cyclic redundancy check - Wikipedia, the free encyclopedia
		A cyclic redundancy check (CRC) is a type of hash function used to produce a checksum, which is a small number of bits, from a large block of data, such as a packet of network traffic or a block of a computer file, in order to detect errors in transmission or storage.
		CRCs are often referred to as "checksums," but such designations are not strictly accurate since, technically, a checksum is calculated through addition, not division.
		Alder-32 Note: D is the string of bytes for which the checksum is to be calculated, and n is the length of D.
	en.wikipedia.org /wiki/Cyclic_redundancy_check (835 words)

	FITS Checksum Proposal
		Verifying that the accumlated checksum is still equal to -0 provides a fast and fairly reliable way to determine that the HDU has not been modified by subsequent data processing operations or corrupted while copying or storing the file on physical media.
		Checksums are used to gain confidence in the continued integrity of all sorts of data.
		The normal procedure is to calculate the checksum of the data on the transmitting side of some communication channel (including magnetic media) and later to compare that checksum with the recalculated checksum on the receiving side.
	heasarc.gsfc.nasa.gov /docs/heasarc/fits/checksum23may02/checksum23may02.html (3808 words)

	CHECKSUM 1L "19 June 1992" (Site not responding. Last check: 2007-10-19)
		If the checksum has previously been installed in the input file, and the input file has not been corrupted since then, the output file will be identical to the input file.
		A zero status code is returned for a correct checksum, and a non-zero one otherwise; in UNIX, the status code may be conveniently tested in shell scripts.
		The file checksum is therefore independent of the particular representation of end-of-line.
	www.math.utah.edu:8080 /ftp/pub/misc/checksum-1-03.html (578 words)

	Fletcher's Checksum (Site not responding. Last check: 2007-10-19)
		This is Fletcher's checksum (ref. 16-18) which is a variant of the 1's complement checksum that is tuned to trap bit error patterns similar to those trapped by a CRC.
		The checksum is divided into two (16 bit) pieces--a straight 1's complement sum and a higher order sum of the running sums.
		Other checksums are also options in the binary case, especially if the checksum fields can be located at the end of the file, which simplifies the arithmetic significantly.
	heasarc.gsfc.nasa.gov /docs/heasarc/ofwg/docs/general/checksum/node20.html (209 words)

	Checksum Algorithm
		Checksums take on various forms, depending upon the nature of the transmission and the needed reliability.
		For example, the simplest checksum is to sum up all the bytes of a transmission, computing the sum in an 8-bit counter.
		This is one consideration as to why network packets are not sent as megabyte packets; errors in a megabyte transmission might result in the same checksum as the error-free transmission, while for short packet sizes (e.g., 4K, or 1500 bytes) the chances are so low as to not be of any concern in practical networking.
	www.flounder.com /checksum.htm (1474 words)

	What's an ISBN, a UPC, and a checksum
		The first nine characters are chosen as the unique number; the tenth is a checksum.
		A checksum is a digit that is the product of a series of mathematical operations on the first digits that help doublecheck that the other digits are correctly entered into a system when typed manually or barcode scanned.
		The EAN checksum was somewhat hidden, but we found the information here.
	www.isbn.nu /whatsanisbn.html (367 words)

	TCP option 14, TCP Alternate Checksum Request.
		Definition of the option: the TCP Alternate Checksum Request Option may be sent in a SYN segment by a TCP to indicate that the TCP is prepared to both generate and receive checksums based on an alternate algorithm.
		During communication, the alternate checksum replaces the regular TCP checksum in the checksum field of the TCP header.
		Should the alternate checksum require more than 2 bytes to transmit, the checksum may either be moved into a TCP Alternate Checksum Data Option and the checksum field of the TCP header be sent as 0, or the data may be split between the header field and the option.
	www.networksorcery.com /enp/protocol/tcp/option014.htm (371 words)

	[No title]
		The first octet of the data portion of the datagram is a ICMP type field; the value of this field determines the format of the remaining data.
		Checksum The checksum is the 16-bit ones's complement of the one's complement sum of the ICMP message starting with the ICMP Type.
		Code 0 Checksum The checksum is the 16-bit ones's complement of the one's complement sum of the ICMP message starting with the ICMP Type.
	www.ietf.org /rfc/rfc792.txt (3481 words)

	Pescados Software - checkSum+
		These files store "checksum" information about files, and will allow this and other applications know if the related files are or not corrupted.
		Please, note that the files in question must be in the same folder as your checksum file.
		We also use ed2k_hash (available at SourceForge) to generate the md4 algorithm specific for the mlnet network, and sha2 for all the sha2 algorithms (thanks to Aaron Gifford).
	homepage.mac.com /julifos/soft/checksum (802 words)

	[No title]
		Should the alternate checksum require more than 2 octets to transmit, the checksum may either be moved into a TCP Alternate Checksum Data Option and the checksum field of the TCP header be sent as 0, or the data may be split between the header field and the option.
		Alternate checksum negotiation proceeds as follows: A SYN segment used to originate a connection may contain the Alternate Checksum Request Option, which specifies an alternate checksum-calculation algorithm to be used for the connection.
		Whether the checksum is split between the checksum field in the TCP header and the option or the entire checksum is placed in the option is determined on a checksum by checksum basis.
	www.ietf.org /rfc/rfc1146.txt (1320 words)

	6.4.1. The CRC-32 Checksum (crc32) (Site not responding. Last check: 2007-10-19)
		The CRC-32 checksum calculates a checksum based on a cyclic redundancy check as described in ISO 3309 [14].
		The resulting checksum is four (4) octets in length.
		The use of collision-proof checksums is recommended for environments where such attacks represent a significant threat.
	www.freesoft.org /CIE/RFC/1510/78.htm (74 words)

	FITS Checksum Verification in the NOAO Archive
		Various checksums may be calculated for FITS as for other data, but the results must be kept separate from the FITS file since writing the value into the header will change the checksum.
		The checksum of each FITS file is forced to zero by writing the complement of the calculated checksum into the header.
		The checksum of the data records is written into a separate header keyword and is not recomputed unless the data are modified.
	www.adass.org /adass/proceedings/adass94/seamanr.html (1237 words)

	Checksum Classes (Site not responding. Last check: 2007-10-19)
		The Checksum classes are used to compute checksums for arbitrary binary streams.
		Computes a CRC16 or CRC32 checksum, a 16 or 32-bit value which is an effective checksum of the data, for validating a data transmission.
		This can be computationally relatively expensive as compared to the rest of the checksum process, so it is wise to create one of these objects only once, and reuse it as needed.
	yaaf.sourceforge.net /docs/quickrefguide/checksum.html (677 words)

	CHECKSUM (Transact-SQL Reference (SQL Server))
		If the arguments to CHECKSUM are columns, and an index is built over the computed CHECKSUM value, the result is a hash index, which can be used for equality searches over the columns.
		CHECKSUM satisfies the properties of a hash function: CHECKSUM applied over any two lists of expressions returns the same value if the corresponding elements of the two lists have the same type and are equal when compared using the equals (=) operator.
		The checksum index can be used as a hash index, particularly to improve indexing speed when the column to be indexed is a long character column.
	msdn.microsoft.com /library/en-us/tsqlref/ts_ca-co_9p2h.asp?frame=true (556 words)

	RFC 1071 (rfc1071) - Computing the Internet checksum
		This is a consequence of the "negative" number in the checksum field exactly cancelling the contribution of the rest of the packet.
		Placement of the checksum field in the packet is critical and the CRC cannot be incrementally modified.
		The problem with attempting to validate checksums in the frontend is that it destroys the end-to-end character of the checksum.
	www.faqs.org /rfcs/rfc1071.html (5649 words)

	RFC 1624 (rfc1624) - Computation of the Internet Checksum via Incremental
		Introduction Incremental checksum update is useful in speeding up several types of operations routinely performed on IP packets, such as TTL update, IP fragmentation, and source route update.
		Since there is guaranteed to be at least one non-zero field in the IP header, and the checksum field in the protocol header is the complement of the sum, the checksum field can never contain ~(+0), which is -0 (0xFFFF).
		It is recommended that intermediate systems compute incremental checksum using the method described in this document, and end systems verify checksum as per the method described in RFC 1071.
	www.faqs.org /rfcs/rfc1624.html (1015 words)

	Checksum
		The checksum number is represented as a 16-bit unsigned number, encompassing the range 0...
		The checksum program must itself be portable and freely available, because verification of the checksum may be required on any machine that the file is transported to.
		The file must contain the checksum, but somehow, the checksum itself must not be counted when the checksum is computed.
	www.math.utah.edu /~beebe/software/filehdr/node15.html (843 words)

	Checksum Transmission
		Then a stronger checksum, strong enough to prevent blocks being identified as in common with the target file incorrectly, must be used for verification.
		The download time is proportional to the amount of checksum data we transmit; part of the processing time on the client is proportional to the number of strong checksums that need to be calculated.
		The number of false matches on weak checksums (and hence unnecessary strong checksum calculations) are proportinal to the number of hashes calculated by the client (which is roughly the file size on the client) times the likelyhood of a false match.
	zsync.moria.org.uk /paper/ch02s03.html (882 words)

	Checksum Task
		If you set the verifyproperty attribute, property specifies the checksum you expect to be generated (the checksum itself, not a name of a property containing the checksum).
		The individual checksums and the relative paths to the files within the filesets they are defined in will be used to compute this checksum.
		When this is set, the generated checksum is not written to a file or property, but rather, the content of the file or property is used to check against the generated checksum.
	ant.apache.org /manual/CoreTasks/checksum.html (635 words)

	CheckSum
		CheckSum strives to protect security of your information.
		In some circumstances, CheckSum may request personal information from you, such as your name, e-mail address, and company name and/or telephone number.
		In addition, CheckSum may use this information for other business purposes, such as to alerting you to products and services that can assist you in your business or assisting in order processing.
	www.checksum.com /privacy.asp (431 words)

	Michael Barr's Embedded Systems Glossary - C
		A checksum is most often used when sending a packet of data over a network or other communications channel.
		One checksum formula is a simple addition, with overflow ignored, wherein the bytes of the packet are added together into a variable of a fixed size/width (say, 16 bits) as they are sent.
		The checksum is typically sent at the end of the packet and used at the receiving end to confirm the integrity of the preceding data.
	www.netrino.com /Publications/Glossary/C.html (773 words)

	Definition: checksum (Site not responding. Last check: 2007-10-19)
		Note 2: The checksum is calculated by treating the data items as numeric values.
		Note 3: Checksums are used in error detecting and correcting.
		Note: Checksums are stored or transmitted with data and are intended to detect data integrity problems.
	www.its.bldrdoc.gov /fs-1037/dir-007/_0950.htm (101 words)

	CheckSum In-Circuit Test (ICT) Equipment
		Expand your Agilent in-circuit test (ICT) capacity at a fraction of the cost
		CheckSum and Corelis provide a complete Boundary-Scan solution
		See how one high-volume manufacturer slashed annual test costs by 60%.
	www.checksum.com (76 words)

	RFC 1146 (rfc1146) - TCP alternate checksum options
		The octets covered by this algorithm should be the same as those over which the standard TCP checksum calculation is performed, with the pseudoheader being D[1] through D[12] and the TCP header beginning at D[13].
		Note that, unlike the OSI version of the Fletcher checksum, this checksum does not adjust the check bytes so that the receiver checksum is 0.
		The two bytes reserved for B should be set to zero during the calculation of the checksum.
	www.faqs.org /rfcs/rfc1146.html (1300 words)

	REBOL: Checksum - Function Summary
		Generally, a checksum is a number which accompanies data to verify that the data has not changed (did not have errors).
		The /TCP refinement is used to compute the standard TCP networking checksum.
		This is a weak but fast checksum method.
	www.rebol.com /docs/words/wchecksum.html (87 words)

	Checksum Transformation
		The Checksum Transformation computes a hash value, the checksum, across one or more columns, returning the result in the Checksum output column.
		All input columns are passed through the transformation unaltered, those selected are used to generate the checksum which is passed out through a single output column, Checksum.
		The Checksum output column is in addition to all existing columns within the pipeline buffer.
	www.sqlis.com /default.aspx?21 (236 words)

	Advanced CheckSum Verifier - SFV and MD5 utility for Windows, GUI replacement of MD5SUM.
		Another good feature of the checksums is the fixed length of the checksum irrespective of the size of an source file.
		These features of the checksums may be used for revealing the damaged files or compare two files for identity.
		Adding an little checksum file to your data files will allow in further easily to verify their integrity at any time.
	www.irnis.net /soft/acsv (1054 words)

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