A Vault9 vault opens with two things: your pattern or passphrase, and a Secret Key that your iPhone makes for you (or Face ID, if you turn it on). A copy of your vault files does not contain the Secret Key. To open such a copy, someone needs the Secret Key and your pattern or passphrase.
Pattern or passphrase
You pick one when you create the vault, and you can switch later in Settings.
A pattern is a line through dots on a 6 × 6 grid. It needs at least 8 dots and 3 changes of direction, and the order of the dots matters. We recommend 12 to 15 dots. A passphrase is typed text of at least 12 characters. We recommend 4 or more random words, and the app can make a 5-word passphrase for you.
Our advice is the passphrase if your lock must hold up against a person who has your phone. It is stronger. A pattern is faster to enter. The strength meter helps either way, and the app rejects very common choices: the letters L, Z, S and N, and squares around the edge.
Vault9 never stores your pattern or passphrase, not even in a scrambled form.
A key that stays on the phone
The Secret Key is a random 128-bit code. You do not choose it and you do not need to remember it. Your iPhone keeps it in the Keychain (the protected storage of iOS), set to “this device only”. An iPhone backup (iCloud or computer) and a Quick Start transfer do not carry it.
You get a copy on your Emergency Kit, a one-page PDF with the key as text and as a QR code. You need the kit when you move to a new iPhone.
The effect is that the iCloud backup and a copy of the phone’s storage have no Secret Key in them. The cost is the kit. If the phone is gone, the kit holds the only other copy of the key.
Where this lock stops
The iPhone holds the Secret Key, so someone who has your phone only needs to guess your pattern or passphrase. iOS makes it hard, but not impossible, to copy the key out of the Keychain. From the 5th wrong try in a row, the app makes them wait: 1 minute, then 2, 4, 8, 16, 32 and at most 60 minutes. The app never deletes the vault after wrong tries, so guessing is slowed, not stopped. A long passphrase is the best answer. More on this in the stolen iPhone page.
Three more limits:
- A kit with your pattern or passphrase written on it opens your vault for anyone who also has a copy of your files. Keep the kit like a passport.
- Vault9 does not protect you if someone holds your unlocked phone, or if malware runs on it.
- If you forget your pattern or passphrase and did not write it on the kit, you cannot open the vault. We cannot open it for you.
How the encryption works
Vault9 encrypts each file with AES-256-GCM, with a separate key for each file. This mode also detects changes: if a file is damaged or altered, the app refuses to show it. The app stretches your pattern or passphrase with PBKDF2-HMAC-SHA512 and 600,000 iterations, so each guess costs real work. The Secret Key is part of the same process, and neither secret alone gives the key that opens your files.
