If I move my file to a new computer or its date changes, is my EMOZ proof still valid?
Yes. Your proof is anchored to the content of your file, not to its dates, its name, or where you keep it.
When you create a timestamp, EMOZ computes a fingerprint (a SHA-256 hash) from the exact bytes of your file. That fingerprint ignores everything the operating system stores around the file: the "Date created", "Date modified" and "Last opened" dates, the file name, the folder, and system tags or attributes. On both macOS and Windows those live in the filesystem, next to the file, not inside it, so they are never part of the fingerprint.
This means all of the following are safe and leave your proof intact:
- Opening, playing or viewing the file
- Copying, moving or renaming it
- Backing it up and restoring it (Time Machine, File History, an external drive)
- Moving everything to a new computer
- Any of the file's dates changing as a result
The only thing that changes the fingerprint is a change to the file's actual content. That happens when an application re-saves or re-exports the file, or edits metadata that is stored inside it. For example, a photo's "Date Taken" (EXIF, i.e. the metadata inside the photo) or a song's title and artist tags (ID3) are stored inside the file, so editing them changes the fingerprint, while simply moving the file does not.
A couple of habits make this a non-issue:
- Keep the original untouched. Archive a clean copy of the exact file you timestamped, and do any further editing on a separate copy. If you change the master later, timestamp the new version too.
- Even better, zip them together. Put your EMOZ certificate (the PDF) and the original file into a single ZIP archive. A ZIP is a container that stores your file's exact bytes, so the two stay together and the original is shielded from apps that might otherwise re-tag it. Extracting the file later gives back byte-for-byte the same file, so its fingerprint still matches your certificate.
- You can always check. Your certificate shows the fingerprint. Recompute your file's fingerprint (you can use our hash calculator) and compare it: if they match, the file is intact and your proof holds; if they differ, that copy was modified and you should go back to your archived original.
And even in the worst case, where a copy gets altered, the record on the blockchain stays permanent and unchanged: it always proves that this exact fingerprint existed on that date. But the blockchain holds the fingerprint, not your file, so you do need the original file itself to make use of the proof: you demonstrate your case by presenting a file whose fingerprint matches the record. That is precisely why keeping the exact, unaltered original safe is the one thing that really matters. Without it (or a byte-for-byte copy of it) you have the record, but nothing to match against it.