In the OAIS reference model ( ISO, 2012 ) these are the producers, the OAIS itself is the repository, and the consumers.Ī short video explaining the basics of Integrity (Fixity) Checking in Digital Preservation
This allows a ‘chain of custody’ to be established between those who produce or supply the digital materials, those responsible for its ongoing storage, and those who need to use the digital material that has been stored. To be given to users of the file in the future so they know that the file has been correctly retrieved from storage and delivered to them.To know that file fixity has been maintained when that file is being stored.To know that a file has been correctly received from a content owner or source and then transferred successfully to preservation storage.It is important to note that whilst checksums can be used to detect if the contents of a file have changed, they do not tell you where in the file that the change has occurred.
Checksums are typically created using cryptographic techniques and can be generated using a range of readily available and open source tools. However, files are currently the most common way of storing digital materials and fixity of files can established and monitored through the use of checksums.Ī checksum on a file is a ‘digital fingerprint’ whereby even the smallest change to the file will cause the checksum to change completely. Fixity could be applied to images or video inside an audiovisual object, to individual files within a zip, to metadata inside an XML structure, to records in a database, or to objects in an object store.
#Generate checksum series
Fixity doesn’t just apply to files, but to any digital object that has a series of bits inside it where that ‘bitstream’ needs to be kept intact with the knowledge that it hasn’t changed. “Fixity, in the preservation sense, means the assurance that a digital file has remained unchanged, i.e. Illustration by Jørgen Stamp digitalbevaring.dk CC BY 2.5 Denmark Fixity
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