NullKey 
Keep one protected master copy
Passport and ID scans usually end up in several places at once: the gallery, the downloads folder, a message thread and a cloud backup. Each extra copy is another place to check and another place a file can leak from. The first job is to find them all, then choose one protected home for the master copy.
An encrypted vault is one option for that master copy. It protects stored contents with encryption and a secret you hold, but a readable copy you make later sits outside that protection.
Why loose copies are a problem
A scan in the downloads folder can be read by any app your permissions allow to see storage. A gallery copy appears in photo views and may be uploaded by a backup service. A scan sent in a chat also sits on the recipient's phone and may sit in their backups. None of this means something has gone wrong, but it does mean you need to know where your copies are.
Screenshots are a common hidden copy. Each time you capture a passport page, check whether the image has landed in your gallery and where it is synced.
A routine for scans
Run through this list whenever you add a new document, rather than letting copies build up.
- Search for scans on the phone, including screenshots, downloads and attachments.
- Choose one place for the master copy and write down where it is.
- Import the master copies and check each one at full size.
- Make an encrypted backup and keep its passphrase or recovery key apart from the phone.
- Delete stray copies only after the backup has been checked and restored into a test vault.
How NullKey handles this
NullKey stores photos, files and notes encrypted in the app's private storage. You unlock the vault with your passphrase, or with a biometric option or another method you have enabled. Photos open inside the vault. The app has no in-app PDF viewer, so a scan saved as a PDF needs a readable export before another app can show it.
Limit: that export is no longer encrypted by the app, and the vault cannot protect a scan that sits visibly on an unlocked phone. If you delete a scan without a checked backup, Alvento cannot recreate it.
Name and store with care
A scan is most useful when you can find it quickly and still recognise it. Give files a plain label that describes the document without spelling out the number, because file names can show up in lists, notifications and sync activity. Keep the labelling consistent, so an older backup and a newer one are easy to tell apart.
Because you rarely need these scans, one checked copy in the vault is usually enough, kept alongside the physical document rather than instead of it.
