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Checksum
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{{Short description|Data used to detect errors in other data}} {{more citations needed|date=January 2024}} [[File:Checksum.svg|thumb|330px|right|Effect of a typical checksum function (the Unix<code>[[cksum]]</code> utility)]] A '''checksum''' is a small-sized [[Block (data storage)|block]] of data derived from another block of [[digital data]] for the purpose of [[error detection|detecting errors]] that may have been introduced during its [[telecommunications|transmission]] or [[computer storage|storage]]. By themselves, checksums are often used to verify [[data integrity]] but are not relied upon to verify [[data authenticity]].<ref>{{Cite web |title=Definition of CHECKSUM |url=https://www.merriam-webster.com/dictionary/checksum |access-date=2022-03-10 |website=Merriam-Webster |language=en |archive-date=2022-03-10 |archive-url=https://web.archive.org/web/20220310132715/https://www.merriam-webster.com/dictionary/checksum |url-status=live }}</ref> The [[algorithm|procedure]] which generates this checksum is called a '''checksum function''' or '''checksum algorithm'''. Depending on its design goals, a good checksum algorithm usually outputs a significantly different value, even for small changes made to the input.<ref>{{Cite web |last=Hoffman |first=Chris |title=What Is a Checksum (and Why Should You Care)? |url=https://www.howtogeek.com/363735/what-is-a-checksum-and-why-should-you-care/ |access-date=2022-03-10 |website=How-To Geek |date=30 September 2019 |language=en-US |archive-date=2022-03-09 |archive-url=https://web.archive.org/web/20220309114058/https://www.howtogeek.com/363735/what-is-a-checksum-and-why-should-you-care/ |url-status=live }}</ref> This is especially true of [[cryptographic hash function]]s, which may be used to detect many data corruption errors and verify overall [[data integrity]]; if the computed checksum for the current data input matches the stored value of a previously computed checksum, there is a very high probability the data has not been accidentally altered or corrupted. Checksum functions are related to [[hash function]]s, [[fingerprint (computing)|fingerprint]]s, [[randomization function]]s, and [[cryptographic hash function]]s. However, each of those concepts has different applications and therefore different design goals. For instance, a function returning the start of a string can provide a hash appropriate for some applications but will never be a suitable checksum. Checksums are used as [[cryptographic primitive]]s in larger authentication algorithms. For cryptographic systems with these two specific design goals{{Clarify|reason=What two specific design goals?|date=March 2023}}, see [[HMAC]]. [[Check digit]]s and [[parity bit]]s are special cases of checksums, appropriate for small blocks of data (such as [[Social Security number]]s, [[bank account]] numbers, [[computer word]]s, single [[byte]]s, etc.). Some [[error-correcting code]]s are based on special checksums which not only detect common errors but also allow the original data to be recovered in certain cases.
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