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Calendar Sync

Calendars contain some of your most sensitive data; use products that implement E2EE at rest to prevent a provider from reading them.


Tuta logo Tuta logo

Tuta offers a free and encrypted calendar across their supported platforms. Features include: automatic E2EE of all data, sharing features, import/export functionality, multi-factor authentication, and more.

Multiple calendars and extended sharing functionality is limited to paid subscribers.



Proton Calendar


Proton Calendar is an encrypted calendar service available to Proton members via web or mobile clients. Features include: automatic E2EE of all data, sharing features, import/export functionality, and more. Those on the free tier gain access to 3 calendars, whereas paid subscribers can create up to 25 calendars. Extended sharing functionality is also limited to paid subscribers.



Unfortunately, as of May 2024 Proton has still not released the source code for their mobile Calendar app on Android or iOS, and only the former has been audited. Proton Calendar's web client is open source, however, and has been audited.


Please note we are not affiliated with any of the projects we recommend. In addition to our standard criteria, we have developed a clear set of requirements to allow us to provide objective recommendations. We suggest you familiarize yourself with this list before choosing to use a project, and conduct your own research to ensure it's the right choice for you.

Minimum Qualifications

  • Must sync and store information with E2EE to ensure data is not visible to the service provider.


Our best-case criteria represents what we would like to see from the perfect project in this category. Our recommendations may not include any or all of this functionality, but those which do may rank higher than others on this page.

  • Should integrate with native OS calendar and contact management apps if applicable.

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