checksum


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checksum

(storage, communications)
A computed value which depends on the contents of a block of data and which is transmitted or stored along with the data in order to detect corruption of the data. The receiving system recomputes the checksum based upon the received data and compares this value with the one sent with the data. If the two values are the same, the receiver has some confidence that the data was received correctly.

The checksum may be 8 bits (modulo 256 sum), 16, 32, or some other size. It is computed by summing the bytes or words of the data block ignoring overflow. The checksum may be negated so that the total of the data words plus the checksum is zero.

Internet packets use a 32-bit checksum.

See also digital signature, cyclic redundancy check.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

checksum

A value used to ensure data are stored or transmitted without error. It is created by calculating the binary values in a block of data using some algorithm and storing the results with the data. When the data are retrieved from memory or received at the other end of a network, a new checksum is computed and matched against the existing checksum. A non-match indicates an error.

Just as a check digit tests the accuracy of a single number, a checksum tests a block of data. Checksums detect single bit errors and some multiple bit errors, but are not as effective as the CRC method. Checksums are also used by the Sophos antivirus software to determine if a file has changed since the last time it was scanned for a virus. See ECC memory and Sophos.
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References in periodicals archive ?
If a node tries to tamper with the data before forwarding the packet, the checksum will not match and the Monitor will generate a negative event against that node.
They add encrypted parameters such as checksum or signature into the requests for data tampering detection.
Using Library of Congress' Bagger tool, the three tiers are "bagged" into a folder, and checksums are run on all three files.
Checksum was originally a simple addition of all bytes (sum...).
All commands are stored with a Fletcher-16 checksum and queue entries with invalid checksum are discarded.
(ii) Measurement data from sensors are verified in the sensor node via checksum verification before transmission, such that sensor nodes only transmit meaningful information to the network.
The first approach hid information in DNA binary strands and the second designed a molecular checksum. Decryption is done using PCR and subsequent gel electrophoresis.
Figure 5 shows the logical structure of a preservation copy: it includes (a) a descriptive sheet that lists all of the files in the preservation copy, the provenance of the document, the details about each audio file, and the venue of the transfer together with the person responsible for the creation of the copy; (b) the audio signal; (c) first-level metadata: checksum of the audio files; second-level metadata: technical specifications of the file formats included in the preservation copy (bwf, pdf, etc.); (d) photographical documentation of the carrier, its case, and the accompanying material and a technical sheet describing the transfer system.
Also an IETF standard, this nearly-identical-to-UDP protocol differs in one key way: It has a checksum (a number that is the result of a logical operation performed on all the data, which if it differs after a transfer indicates that the data is corrupt) and a checksum coverage range that that checksum applies to, whereas vanilla UDP--optionally in IPv4, and always in IPv6--has just a simple checksum on the whole datagram and if present the checksum covers the entire payload.
Today the concept of 'signing' software is becoming commonplace and will contain metadata such as the software author, a checksum to verify that the object has not been altered and versioning information.
Electronic signatures are possible, along with a checksum (similar to a hash function) to ensure integrity.