Heratio Help Center article. Category: Digital Preservation.

Fixity and checksums

What is fixity?

Fixity is the assurance that a file has not changed - not by a single bit - since it entered your archive. It is the most basic integrity control in digital preservation: it lets you prove that the file you hold today is exactly the file you received.

How Heratio checks it

Heratio computes a checksum (a cryptographic fingerprint, by default SHA-256) for each digital file. The fingerprint is stored. Later, Heratio recomputes it and compares:

• Match - the file is intact.
• Mismatch or missing - the file has been corrupted, truncated, or tampered with, and is flagged for investigation.

Storage media degrade silently over time ("bit rot"), so regular rechecking is essential.

Doing it in Heratio

• Generate a checksum for a record from its preservation view, or via the preservation dashboard.
• Verify a single record with the "Verify fixity" action on /admin/preservation/object/{id}.
• Verify in bulk on a schedule: Heratio runs due fixity checks automatically (set up under /admin/preservation/scheduler), and an administrator can run a sweep that targets files not checked recently.
• Review results in the fixity log at /admin/preservation/fixity-log. Every check is also recorded as a PREMIS event under /admin/preservation/events.

Self-healing

If you have configured backup / replication targets, a failed fixity check can trigger automatic repair: Heratio finds a copy on a replication target, verifies that copy against the stored checksum, restores the damaged file, and logs the repair. Without replicas, a failure can still be detected and logged, but not automatically healed - so keeping verified copies matters.

Choosing an algorithm

See also

• Digital preservation overview (help)
• OAIS packages: SIP, AIP, DIP (help)
• Your preservation maturity score (help: "Preservation Maturity Self-Assessment")