Stamp it and keep it safe.

What a timestamp does

A timestamp proves your file existed on a given day. It doesn’t reveal what’s in the file: only a fingerprint of the file leaves your computer. The free OpenTimestamps servers record that fingerprint in the Bitcoin blockchain, and later anyone you choose to show can check the date.

Stamp it in your browser

On a computer:

1. Go to opentimestamps.org.
2. Find the box that says Drop here a file to stamp.
3. Drag your export file onto that box.
4. Wait a moment. A small file ending in .ots downloads by itself. That’s your proof.
5. Move the .ots file into the same folder as your export.
6. Do the same for your memories text file, if you made one.

The page talks about uploading your document, but OpenTimestamps says the fingerprint is calculated in your browser, so the file itself stays on your computer. Leave both files exactly as they are, names included. If the export changes at all, even by one character, the timestamp won’t match it.

Pending is normal

Your proof starts out pending. It’s complete once the timestamp servers have written to Bitcoin, which takes a few hours. To check it the next day, drop the .ots file onto the same box, then drop your export when the page asks for the stamped file. A Bitcoin attestation means it’s complete. Keep the .ots file whatever the page says, because the timestamp servers hold what’s needed to finish it later.

If you’re comfortable in Terminal, OpenTimestamps also has a command-line client. Its site shows how to install it, and its ots upgrade command writes the finished proof into your .ots file.

Keep it safe until it’s sealed

Your export holds your conversations, unencrypted. Until you can seal it:

• Keep it on your own computer, in a folder that doesn’t sync to the cloud: not in iCloud Drive, Dropbox, Google Drive or OneDrive.
• Check whether iCloud syncs your Desktop and Documents. Open System Settings, click your name, then iCloud, then Drive (it may say iCloud Drive), and look at Desktop & Documents Folders. If it’s on, don’t keep the export on your Desktop or in Documents. On Windows, OneDrive can back up those folders too.
• Don’t upload it to any website or app. Stamping doesn’t count: it sends only a fingerprint, never the file.
• Turn on FileVault on your Mac if it isn’t on already, so nobody can get at your files without your login password. Choose the Apple menu, then System Settings, click Privacy & Security, then FileVault (you may need to scroll down), and turn it on. If you’re given a recovery key, keep it somewhere safe: Apple warns that if you lose both your password and the key, your files are gone for good.
• Make a second copy on a USB drive, with its .ots file, and keep the drive somewhere private. Anyone who has the drive can read your export.

We’ll never ask you to send us your export, your password or your files. The Lifeboat Kit, planned for December, runs on your own Mac, and we hold nothing.