You uploaded family photos to Google Drive.
You uploaded tax returns to Dropbox.
You uploaded a scan of your passport to iCloud.
You assumed they were private. They are not, by default.
Google's terms of service authorize content scanning of files in Drive. Dropbox does the same. iCloud does the same. On a valid legal request, any of them hands the files over.
A small team in Germany spent more than a decade building the tool that fixes this.
It is called Cryptomator.
You install it. You point it at your Dropbox folder. It creates a vault. You drop files in. They get encrypted on your computer with AES-256 before they ever leave for the cloud.
Dropbox sees encrypted blobs. Google sees encrypted blobs. iCloud sees encrypted blobs. Only you have the password.
Works with Dropbox, Google Drive, OneDrive, MEGA, pCloud, ownCloud, Nextcloud. Works on Windows, macOS, Linux.
File contents encrypted. File names encrypted. Folder structure obfuscated. No accounts. No telemetry.
Honest disclosure. The cloud still sees the vault exists, its size, and when it syncs. Cryptomator hides what is inside, not the vault itself.
Receipts.
15,245 stars. 1,296 forks. GPL-3.0. Java. Last commit five days ago.
Desktop apps for Windows, macOS, Linux: free forever.
Mobile apps: one-time purchase. No subscription.
Built by Skymatic, near Bonn. Ten years old this March.
You did not buy cloud storage. You rented a glass house.
Cryptomator gives you curtains.
(Link in the comments)