Fixity
The property of a digital file remaining unchanged over time, verified using checksums so that any corruption or alteration can be detected.
Fixity refers to a digital object’s state of being fixed — unchanged — over time. In digital preservation, fixity is verified by computing a checksum (a cryptographic hash such as SHA-256) when a file is ingested and periodically recomputing it. If the checksum ever differs, the file has been altered or corrupted, and a clean copy can be restored from redundant storage.
Fixity checking is how a preservation program proves the integrity of its holdings: it provides evidence that a record is bit-for-bit identical to what was originally preserved. This supports both trustworthiness and chain of custody, and it is a routine, automated part of any mature digital preservation repository.