I'm thinking about moving my calendars and contacts to "the cloud". For privacy reasons I'll only consider end-to-end encrypted providers. Such exist.

Obviously (?), full end-to-end encryption and, say, serving CalDAV are incompatible requirements. The best I can hope for is to store the information as synced files which are read and written locally. Let's assume a single-user environment for simplicity, i.e. we don't have to care about concurrent updates to these files.

What are existing solutions for this? I'm interested in clients (or plugins for software) on Android and Linux.

3 Answers 3


It is possible to leverage secure cloud services together with standard tools.

For contacts, CardBook for Thunderbird can use external VCF files as storage for address books. This is part of the addressbook creation wizard.

For calendars, Thunderbird's built-in Lightning can do the same for VCS files, if a little more obscure: synchronize to a remote calendar but enter file:///path/to/file (for GNU/Linux and presumably MAC; might look different on Windows) as address.

Put those files in a folder that is synced with the cloud storage provider of your choice; I use Tresorit which works just fine.
For an additional layer of safety, you can also (manually) revision the files with Git.

I am not aware of how to connect such a setup to an android phone.


I'd look at getting your own VPS from Linode.com or similar and configuring your own private "cloud" storage. Quick search suggests multiple CalDAV servers available, or something like Citadel (email/calendar/listserv/etc) may suit your needs.

  • "For privacy reasons I'll only consider end-to-end encrypted providers."
    – Raphael
    Oct 28, 2018 at 20:17

For contacts and calendars, as far as I know, there is only EteSync (open source, but not quite cheap).

For calendars alone, there are now several platform-independent solutions:

Proton Calendar: Android and Browser-based

Tutanota; Web and desktop clients, in German

Calendar Lock PEA: Desktop client (I myself am developer)

Peergor Calendar: Relatively new

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