ProtonDrive (from the makers of ProtonMail and ProtonVPN) is in the final stages of development before it gets a beta launch later in 2020. The team revealed its end-to-end encryption security in a blog post.
Files and folders are arranged in a tree structure. Therefore, there is a recurring pattern where a file or folder’s asymmetric key is locked with a passphrase, which in turn is encrypted with the asymmetric key of their parent folder. All passphrases are signed with the address key of the user, without which a malicious server could forge the contents of the tree.
Check It Out: ProtonDrive’s End-to-End Encryption Security Revealed