nextcloud-docs/admin_manual/configuration/configuration_encryption.rst

Using Server-Side Encryption
============================

ownCloud includes a server-side encryption application. The Encryption app 
encrypts all files stored on the ownCloud server, and all files on remote 
storage that is connected to your ownCloud server. Encryption and decryption are 
performed on the ownCloud server. All files sent to remote storage (for example 
Dropbox and Google Drive) will be encrypted by the ownCloud server, and upon 
retrieval, decrypted before serving them to you and anyone you have shared them with.

When files on external storage are encrypted in ownCloud, you cannot share them 
directly from the external storage services, but only through ownCloud sharing 
because the key to decrypt the data never leaves the ownCloud server.

The main purpose of the Encryption app is to protect users' files on remote 
storage, and to do it easily and seamlessly from within ownCloud. 

The Encryption app generates a strong encryption key, which is unlocked by 
user's passwords. So your users don't need to track an extra password, but 
simply log in as they normally do.

Encryption is applied server-wide; it cannot be applied to selected users.

The Encryption app encrypts only the contents of files, and not filenames and 
folder structures.

You should regularly backup all encryption keys to prevent permanent data loss. 
The encryption keys are stored in following folders:

``data/owncloud_private_key`` 
  Recovery key, if enabled, and public share key
``data/public-keys`` 
  Public keys for all users
``data/<user>/files_encryption`` 
  Users' private keys and all other keys necessary to decrypt the users' files
``data/files_encryption``
  private keys and all other keys necessary to decrypt the files stored on a
  system wide external storage

.. note:: Encryption keys are stored only on the ownCloud server, eliminating
   exposure of your data to third party storage providers. The encryption app 
   does **not** protect your data if your ownCloud server is compromised, and it
   does not protect users from snoopy ownCloud admins. This would require client 
   side encryption, which this app does not provide. If your ownCloud server 
   is not connected to any external storage services then it is better to 
   use other encryption tools, such as file-level or whole-disk encryption. Read 
   `How ownCloud uses encryption to protect your data 
   <https://owncloud.org/blog/how-owncloud-uses-encryption-to-protect-your-data/>`_. for 
   more details. 

Enabling the Encryption App
---------------------------

The Encryption app is bundled with ownCloud, so first go to your Apps page to 
enable it.

.. figure:: ../images/encryption1.png

After you click the ``Enable`` button you must log out, and then log back in. 
If you continue to work without logging out, you'll see a yellow banner at 
the top of your Files page that warns you "Encryption App is enabled but your 
keys are not initialized, please log-out and log-in again."

.. figure:: ../images/encryption2.png

When you log out and then log back in, your encryption keys are initialized and 
your files are encrypted. This is a one-time process, and it will take a few 
minutes depending on how many files you have.

.. figure:: ../images/encryption3.png

When the encryption process is complete you'll be returned to your default 
ownCloud page. Every user will go through this process when they log in after 
you enable encryption, and each user will get unique encryption keys. Users can 
still change their passwords whenever they want on their Personal pages.

Sharing Encrypted Files
-----------------------

Only users who have private encryption keys (via logging out and logging back in to 
create their keys) have access to shared encrypted files and folders. Users who have not 
yet created their private encryption keys will not have access to encrypted shared files; 
they will see folders and filenames, but will not be able to open or download the files. 
They will see a yellow warning banner that says "Encryption App is enabled but your keys 
are not initialized, please log-out and log-in again." 

Share owners may need to re-share files after encryption is enabled; users trying to 
access the share will see a message advising them to ask the share owner to re-share the 
file with them. For individual shares, un-share and re-share the file. For group shares, 
share with any individuals who can't access the share. This updates the encryption, and 
then the share owner can remove the individual shares.

.. figure:: ../images/encryption9.png


Decrypting Encrypted Files
--------------------------

You have the option of changing your mind and disabling the Encryption app. 
Just click its Disable button on the Apps page, and when you go to your Files 
page you'll see the yellow banner warning "Encryption was disabled but your 
files are still encrypted. Please go to your personal settings to decrypt your 
files".

.. figure:: ../images/encryption4.png

Go to your Personal page and enter your password in the Encryption removal form, 
and your files will all be decrypted.

.. figure:: ../images/encryption5.png

Your users will also have to follow this step to decrypt their files. If 
something goes wrong with decryption, click the ``Restore Encryption Keys`` 
button to re-encrypt your files, and then review your logfile to see what 
happened. Though it would be very unusual for the decryption to fail as 
decryption is routine and reliable. 

Enabling a File Recovery Key
----------------------------

If you lose your ownCloud password, then you lose access to your encrypted files. If one 
of your users loses their ownCloud password their files are unrecoverable. You 
cannot reset their password in the normal way; you'll see a yellow banner 
warning "Please provide an admin recovery password, otherwise all user data will 
be lost".

To avoid all this, create a Recovery Key. Go to the Encryption section of your 
Admin page and set a recovery key password. Obviously, do not lose this 
password. 

.. figure:: ../images/encryption6.png

Then your users have the option of enabling password recovery on their Personal 
pages. If they do not do this, then the Recovery Key won't work for them.

.. figure:: ../images/encryption7.png

For users who have enabled password recovery, give them a new password and recover access 
to their encrypted files by supplying the Recovery Key on the Users page.

.. figure:: ../images/encryption8.png

Files Not Encrypted
-------------------

Only the data in your files is encrypted, and not the filenames or folder
structures. These files are never encrypted:

- Old files in the trash bin.
- Image thumbnails from the Gallery app.
- Previews from the Files app.
- The search index from the full text search app.
- Third-party app data

There may be other files that are not encrypted; only files that are exposed to 
third-party storage providers are guaranteed to be encrypted.

LDAP and Other External User Back-ends
--------------------------------------

If you use an external user back-end, such as an LDAP or Samba server, and you change a 
user's password on the back-end, the user will be prompted to change their ownCloud login 
to match on their next ownCloud login. The user will need both their old and new passwords 
to do this. If you have enabled the Recovery Key then you can change a user's password in 
the ownCloud Users panel to match their back-end password, and then, of course, notify the 
user and give them their new password.