File fixity

File fixity is a digital preservation term referring to the property of a digital file being fixed, or unchanged.{{cite web | url=http://www.library.yale.edu/iac/DPC/AN_DPC_FixityChecksFinal11.pdf | title=Fixity Checks: Checksums, Message Digests and Digital Signatures Audrey Novak, ILTS | date=November 2006 | archiveurl=https://web.archive.org/web/20150111194253/http://www.library.yale.edu/iac/DPC/AN_DPC_FixityChecksFinal11.pdf | archivedate=2015-01-11}} Fixity checking is the process of verifying that a digital object has not been altered or corrupted.{{cite web|title=fixity check|url=https://www.loc.gov/standards/premis/pif-presentations/rebecca-SKOS/preservationEvents-FixityCheck.html|work=PREMIS 2.0 Preservation Events Collection|publisher=Library of Congress Standards & Research Data Values Registry}} During transfer, a repository may run a fixity check to ensure a transmitted file has not been altered en route. Within the repository, fixity checking is used to ensure that digital files have not been affected by data rot, or other digital preservation dangers.{{cite book|isbn= 9783642168086|last=Giaretta|first=David|title=Advanced Digital Preservation|year=2011}} By itself, fixity checking does not ensure the preservation of a digital file. Instead, it allows a repository to identify which corrupted files to replace with a clean copy from the producer or from a backup.

In practice, a fixity check is most often accomplished by computing checksum or cryptographic hash function values for a file and comparing them to a stored value or through digital signatures.{{cite web|last=Novak|first=Audrey|title=Fixity Checks: Checksums, Message Digests and Digital Signatures|url=http://www.library.yale.edu/iac/DPC/AN_DPC_FixityChecksFinal11.pdf|publisher=ILTS Digital Preservation Committee}} File fixity figures prominently in Preservation Metadata: Implementation Strategies (PREMIS), the Government Printing Office's work on the Authenticity of Electronic Federal Government Publications,{{cite web|title=Authenticity of Electronic Federal Government Publications|url=http://www.gpo.gov/pdfs/authentication/authenticationwhitepaper2011.pdf|publisher=U.S. Government Printing Office}} and fixity checking practices are used by a range of cultural heritage organizations.{{cite web|last=Bailey|first=Jefferson|title=File Fixity and Digital Preservation Storage: More Results from the NDSA Storage Survey|url=http://blogs.loc.gov/digitalpreservation/2012/03/file-fixity-and-digital-preservation-storage-more-results-from-the-ndsa-storage-survey/|work=The Signal: Digital Preservation Blog|publisher=The Library of Congress}}