Fixity

Fixity is the state or quality of being fixed or unchanging over time. In information management and digital preservation, fixity refers to the integrity of digital objects: their contents, structure, and representation remain the same as in a reference or original state. Fixity is a foundational concept for ensuring that digital materials can be accessed, understood, and trusted long after creation.

Fixity is typically established and monitored through fixity values or checksums. Common methods include cryptographic hash functions that produce a fixed-length value from a file, such as MD5, SHA-1, or SHA-256. The resulting fixity value, along with metadata about the algorithm and the date of the check, is stored in a fixity manifest or metadata record. Periodic or event-driven verifications recompute the current fixity value and compare it to the stored one to detect alterations, corruption, or tampering.

Key practices include maintaining robust fixity metadata, using multiple algorithms to guard against algorithm deprecation, and integrating fixity checks into preservation workflows. When a mismatch is detected, teams investigate potential causes (bit rot, transfer errors, intentional modification) and take appropriate corrective actions, such as restoring from a known good copy or re-boxing the object.

Limitations exist: fixity does not protect confidentiality or guarantee long-term accessibility by itself, and hash collisions or compromised storage can undermine it. Therefore, fixity is commonly used in combination with other preservation strategies, including provenance, authenticity measures, and secure, redundant storage. In metadata standards such as PREMIS, fixity information is a standard component of digital object preservation records.