Cloud Calendars vs Proton & Tuta Encrypted Calendars
Proton Calendar and Tuta Calendar encrypt event titles, locations, and descriptions before they leave your device so even the cloud server operator cannot read them—making them the right choice when server-side zero-knowledge cryptography is mandatory. Because iOS EventKit and standard CalDAV require unencrypted client access, encrypted calendars live inside isolated app silos that cannot merge natively with Apple Calendar, Siri, or standard iOS clients. Cloud Calendars serves iPhone and iPad users who need standard interoperability across iCloud, Google, and Microsoft—or account-free on-device local calendars that never touch a cloud server at all—paired with Apple WeatherKit forecasts. Arte Soft develops Cloud Calendars and publishes this comparison.
Feature-by-Feature Comparison Matrix
| Capability | Cloud Calendars | Proton Calendar | Tuta Calendar |
|---|---|---|---|
| Primary privacy model | Account-free local device mode + direct EventKit / Google & Microsoft OAuth | Zero-knowledge end-to-end encrypted (E2EE) cloud storage in Switzerland | Zero-knowledge post-quantum-ready E2EE cloud storage in Germany |
| Two-way iCloud / Google / M365 merge | Full read/write across iCloud/CalDAV, Google (Free) & Microsoft (Premium) | No two-way CalDAV/EventKit sync; supports read-only external ICS subscriptions | Isolated encrypted store; imports/exports ICS snapshots rather than live CalDAV |
| Planning views on iOS | Day, Week, Month, 12-month Year, List & Multi-calendar side-by-side columns | Agenda, Day, 3-Day, Week & Month views | Agenda, Day, Week & Month views inside Tuta Mail/Calendar app |
| Weather integration | Full Apple WeatherKit hub + hourly temp, wind/gusts, UV & rain beside hours | No built-in weather forecasts (avoids location telemetry) | No built-in weather forecasts |
| Account-free offline calendar | Yes — create local on-device calendars without registering any account | Requires a Proton Account (Free or Paid) to open and sync | Requires a Tuta Account (Free or Paid) to open and sync |
| Widgets & Lock Screen | Date+WeatherKit widgets, timed-event Home Screen lists & Live Activity countdown | iOS Up Next / Today Home Screen widgets | Dedicated encrypted agenda widget options |
| External attendee invitations | Standard Google, Microsoft, iCloud & App Clip/link/QR sharing | Sends standard unencrypted ICS email invites to external non-Proton guests | Sends standard or password-protected invites via Tuta Mail |
Why End-to-End Encryption Prevents Standard iOS EventKit Sync
A frequent question from Proton and Tuta users on iPhone is why their encrypted events do not show up inside Apple Calendar, CarPlay, Apple Watch’s system calendar, or third-party viewers. If Proton or Tuta decrypted your schedule into Apple’s shared iOS EventKit database—or exposed an unencrypted CalDAV endpoint—any app granted Calendar permission (and iCloud backups, if enabled) could read the cleartext records, defeating the zero-knowledge guarantee.
Proton offers a read-only secret ICS link if you explicitly choose to share a calendar externally, which Cloud Calendars or iOS Settings can subscribe to as a one-way feed. Conversely, if your threat model is avoiding cloud servers altogether on a single iPhone or iPad, Cloud Calendars lets you create purely local calendars on device without signing into Google, Microsoft, iCloud, or Arte Soft.
Account Sync, Protocol & Platform Support
| Dimension | Cloud Calendars | Proton Calendar | Tuta Calendar |
|---|---|---|---|
| Google & Microsoft OAuth | Direct Google OAuth (Free) & Microsoft OAuth (Premium) | One-time Easy Switch import or read-only ICS URL subscription | Manual .ics file import/export only |
| Apple iCloud & CalDAV | Full two-way EventKit access to iCloud & standard CalDAV accounts | No CalDAV bridge for Calendar (Proton Bridge is Mail-only) | No CalDAV support by cryptographic design |
| ICS URL Subscriptions | Reads subscribed ICS feeds configured in iOS Settings | Subscribes to external ICS links (up to plan limit) & can publish secret ICS link | Supports manual ICS file import and export |
| Server-side data visibility | Local mode stays on device; cloud providers follow Apple/Google/Microsoft policies | Server sees only encrypted ciphertext and minimal timing metadata | Server encrypts subject, body, location, and metadata with user keys |
| Supported Platforms | iPhone & iPad (iOS / iPadOS 18.0+) | iOS, Android, Web & desktop wrapper apps | iOS, Android, Web, macOS, Windows & Linux |
| Offline access | Full local calendar editing + cached iOS store events offline | Cached viewing offline; full sync resumes online | Offline cache available on paid tiers / mobile clients |
Pricing and Threat-Model Scenarios Compared
Privacy is not one uniform setting; different threat models call for different architectures. Journalists, legal teams, and activists protecting cloud-synced schedules across desktop and mobile need E2EE providers like Proton or Tuta, even at the cost of losing CarPlay, EventKit, and multi-provider OAuth convenience.
Professionals and families whose employers or relatives already run on Google Workspace, Microsoft 365, or iCloud gain little from an isolated E2EE calendar if every shared invite immediately travels over standard unencrypted email ICS anyway. For those workflows, Cloud Calendars unifies standard providers on iOS from $0 (Free) or $4.99/year ad-free (Advanced).
Pricing & Best Choice by User Scenario
| User Scenario | Cloud Calendars | Proton / Tuta | Best Choice |
|---|---|---|---|
| Zero-knowledge E2EE cloud sync across iPhone, Web & Linux/Windows | iPhone/iPad only; relies on standard provider clouds or device-local storage | Free basic E2EE calendar; paid plans ~$3.30–$9.99/mo add more calendars & sharing | Proton or Tuta |
| Strictly offline calendar on iPhone with zero cloud account at all | Account-free Local calendars included in Free ($0) or $4.99/yr ad-free | Requires creating a cloud account to initialize mailbox/calendar keys | Cloud Calendars (Local mode) |
| Unifying work Google/Microsoft 365 with personal iCloud on iOS | Two-way Google + iCloud (Free) and Microsoft (Premium $49.99/yr) | Cannot sync two-way with Google, Exchange, or iCloud CalDAV | Cloud Calendars |
| Viewing encrypted Proton schedule read-only beside iCloud + weather | Displays Proton’s published secret ICS URL via iOS Subscriptions + WeatherKit | Creates the secret read-only ICS link (note: publishing link exposes cleartext to URL holders) | Proton + Cloud Calendars |
| Outdoor schedule planning with hourly wind, rain & UV | Built-in Apple WeatherKit station and hourly timeline indicators | No weather integration in either app | Cloud Calendars |
| Encrypted email + calendar bundle under one subscription | Calendar-only iOS app ($0 / $4.99 yr / $49.99 yr) | Proton Unlimited / Mail Plus or Tuta Revolutionary bundles mail + calendar | Proton or Tuta |
What Happens When You Export a Secret ICS Link from Proton
If you publish a Proton Calendar via its "Share via link" ICS feature so iPhone Calendar or Cloud Calendars can read it, Proton must decrypt and re-encrypt that feed for the URL token so standard calendar clients can fetch cleartext iCalendar records over HTTPS.
Treat any secret ICS link like a bearer password: anyone who obtains the URL can read those events without logging in, and you should never publish sensitive medical or legal details over a public ICS feed if your goal was strict end-to-end encryption.
Using Account-Free Local Calendars on iPhone
When you want events to stay exclusively on your iPhone or iPad hardware without syncing to Apple iCloud, Google, or Microsoft, create a Local calendar inside Cloud Calendars and skip account sign-in.
Remember that local-only calendars are not backed up to an external calendar provider—if you lose your phone without an encrypted device backup, local-only schedules cannot be recovered from a web login.
What it looks like
What to do
- Decide first whether your threat model requires cloud-synced E2EE (Proton/Tuta) or device-only local storage / standard OAuth interoperability (Cloud Calendars).
- To run Cloud Calendars without any cloud account, skip Google/Microsoft sign-in and create a Local calendar on your iPhone.
- If you bridge Proton into iOS via a secret ICS link, subscribe in iOS Settings > Apps > Calendar > Calendar Accounts > Add Subscription Calendar.
- Keep sensitive E2EE events inside Proton or Tuta directly rather than exposing them through bearer ICS links.
Questions
- Can Cloud Calendars sync two-way with Proton Calendar or Tuta?
- No. Proton Calendar and Tuta use end-to-end encryption without standard CalDAV or iOS EventKit write access. At most, Proton allows a read-only secret ICS URL subscription, which iOS and Cloud Calendars can display one-way.
- Does Cloud Calendars store my iCloud or Google events on Arte Soft servers?
- No for device, iCloud, Google, and Microsoft sync—those connect directly via Apple EventKit and official Google/Microsoft OAuth. Cloud Calendars account sign-in is only used if you explicitly use Cloud Calendars’ own cross-user calendar/event sharing.
- Can I use Cloud Calendars without creating any account?
- Yes. You can create local calendars directly on your iPhone or iPad with no email registration and no cloud calendar provider required.