Fixity checks
Fixity is the property of a file that has stayed identical to itself. Obscura Vault checks it with SHA-256 checksums, during scheduled audits, and never reports as verified what was not.
SHA-256 is a standardized hash function (FIPS 180-4). It sums up a file as a 256-bit checksum; the slightest change to the file gives a different checksum.
A file's checksum serves as its reference: later checks are compared with it.
An alteration can happen silently: an aging medium, a faulty copy, an unlucky edit. Scheduled audits recompute checksums at regular intervals, without waiting for the day you need the file.
A recomputed checksum that differs from its reference signals an alteration.
“Verified good” applies to a file that was actually read again and whose checksum matches its reference.
A check that could not be completed gives “not verifiable”. Obscura Vault keeps the two results apart: a missing check never counts as a success.
An audit reads files again in full: the whole library, or a single project. The automatic library audit can be set to Never (the default), Every week or Every month; it runs while Vault is open, which checks at launch and then every hour whether an audit is due.
Only a complete audit pushes back the due date. A stopped or failed audit leaves the audit due; an audit that could not read every file (an unplugged disk) is marked incomplete and retried the next day.
Every file read adds a line to the fixity log (date, result, expected and observed checksum), which only ever grows. The Integrity screen and the dashboard show verified, altered, not verifiable and never checked files, and the list of files to examine. Verifying integrity needs no license.
Next step
Obscura Vault is available for macOS. Download it from your Obscura member area, or write to us to learn more.