End-to-end encryption — what it does and what it doesn't

End-to-end encryption (E2EE) encrypts files locally on your device before they’re uploaded to the server. The server can’t decrypt the contents — not even we at xaweho. Sounds great at first, but it comes with hard practical trade-offs. Here’s what you need to know before switching E2EE on.

What E2EE does technically

When you mark a folder as E2EE:

1. A key pair is created on your device (the private key stays local, the public key goes to the server)
2. Files in that folder are encrypted with your public key before upload
3. The server stores only ciphertext (encrypted bytes)
4. When you fetch the file, the client downloads the ciphertext and decrypts locally with the private key

Consequence: the server never sees the plaintext. Even we, with server admin rights, can’t read the files.

Where you can enable E2EE

Per folder, not for the whole cloud:

• Files app in the browser → select a folder → ⓘ sidebar → Enable encryption
• Or in the desktop client via right-click on a folder

Important: only empty folders can be newly E2EE-enabled. Converting existing files in a folder isn’t possible — you’d have to create new folders and move things in.

Requirements

• The E2EE app has to be installed in Administration settings → Apps (inactive by default on xaweho setups, active on request)
• Desktop client v3.5+ or a mobile app with E2EE support
• On first activation a recovery mnemonic is generated — you must keep it safe

Recovery mnemonic — critically important

On activation you’re shown a 12-word phrase:

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With this phrase you can decrypt your E2EE files on a new device. Lose it, and the files are gone — we can’t restore them either.

Recommendation:

• Store it in a password manager (1Password, Bitwarden, KeePass)
• Print it on paper and put it in a safe / bank deposit box
• Don’t store it digitally unprotected (email, cloud notes)

What works with E2EE

• Uploading / downloading files via the desktop client and mobile apps
• Sharing with other Nextcloud users (within the same cloud) — the other user needs an E2EE-capable client too
• File name encryption (file names are encrypted as well; the server only sees generic IDs)

What doesn’t work (well)

No browser editing

You can’t open E2EE files in the browser. The browser can’t decrypt, because the private key isn’t in the browser.

Consequence: no OnlyOffice, no Collabora, no browser PDF viewer for E2EE files. Desktop client / mobile app only.

No public sharing

You can’t create a public link on E2EE files. Non-users can’t decrypt anything — that would defeat the point.

No full-text search

The server can’t index the content. Web search won’t find E2EE files (except by the file name hash, which helps nobody).

WebDAV only partially

WebDAV mounts can’t read E2EE files — the mount client can’t decrypt.

No office co-editing

Since browser editing doesn’t work, there’s no co-editing either. You can only edit files sequentially with a local office suite.

Version history limited

Earlier versions are stored, but only restorable via the desktop client — not via the browser.

When E2EE truly makes sense

Definitely:

• Highly sensitive documents (contracts with confidentiality clauses, patient data in limited scope, attorney-client files)
• You want even us / the provider to have no way of reading the files
• Compliance requirements that explicitly demand zero-knowledge

Not sensible:

• Normal family files, club records — server-side protection is enough
• Files your team wants to edit collaboratively — co-editing doesn’t work
• Photo uploads you want to see in the gallery — the browser gallery can’t decrypt

Limits that remain despite E2EE

E2EE protects the content of the files. Not protected:

• The fact that you have a file (the server sees: you have 50 encrypted files)
• File size (the ciphertext is the same size as the plaintext plus a bit of overhead)
• Timestamps (when what was changed)
• Who the file is shared with (the server needs to know that to make sharing work)

For very high requirements (investigative journalism, etc.) that metadata matters — then better to encrypt locally and sync only backups.

Server-side encryption vs E2EE — the difference

Nextcloud can also encrypt files server-side (an administration setting). That protects the files if someone steals the disk — but the server (i.e. us) can still decrypt, because the key sits on the server.

E2EE is much stricter: even the server admin can’t get in.

At xaweho we encrypt the server hardware’s disks anyway — server-side encryption in Nextcloud adds little on top of that.

The recovery scenario you don’t want

A user story from our setups:

A user enables E2EE on the family cloud. The mnemonic phrase disappears (note misplaced). 2 years later: new smartphone, wants to download files. Doesn’t work. No mnemonic = no access. Files lost forever.

We can’t rescue anything there. Literally nothing.

From our experience: 80% of E2EE activations are later regretted, because the limits are too hard. Before you enable it, think it through three times:

• Do you need browser editing? → No to E2EE
• Do you want co-editing? → No to E2EE
• Are the files really so sensitive that even the hoster must not see them? → Yes to E2EE
• Do you have a clean plan for keeping the recovery mnemonic safe for 10+ years? → Otherwise no

If you decide to go for it anyway

1. Install / enable the End-to-End Encryption app in Nextcloud
2. On one device: open the desktop client, generate the mnemonic, store it safely
3. Mark a test folder as E2EE, upload a test file
4. On a second device: enter the mnemonic, verify the file is readable
5. Only then move “real” data into E2EE folders

Frequently asked questions

Can I enable AND disable E2EE per folder? Enable: yes, on an empty folder. Disable: not directly — you’d have to copy the files to an unencrypted folder, then delete the E2EE folder.

Does the content stay accessible if I change my account password? Yes. The E2EE mnemonic is separate from the account password.

Can I share E2EE folders with other users? Yes, but only if the other user also has an E2EE-capable client. Public sharing doesn’t work.

Does E2EE work with OnlyOffice / Collabora? No. The office server can’t decrypt.

What about backups? We back up the encrypted ciphertext. The backups are exactly as secure as the original — but we can’t decrypt them either.

Recovery mnemonic lost — is there a master key on the admin side? No. Not for private setups. Enterprise configs offer an optional recovery admin key, but that’s an additional setup — not active in the xaweho default.

Can I enable E2EE for the whole cloud? Technically no. It’s a per-folder model. You could mark all top-level folders as E2EE, but delete the default Documents folder with its samples beforehand.

Is E2EE open source? Yes, the code is part of the Nextcloud project. It has been audited by the German Federal Office for Information Security (BSI).

What’s next

• 2FA and login security
• Desktop client
• Sharing links with protection