Sync for Proton

Sync for Proton syncs your Proton Contacts and Proton Calendar into Android's native contacts and calendar, so they work everywhere on your phone: the dialer, lock screen, smartwatch, and any calendar or contacts app. No Google account required.

This repository hosts signed APK releases for installing outside the Google Play Store (for example on GrapheneOS or any de-Googled Android), and the source code of each release. Development happens in a private repository; every release adds one commit here with exactly the source that release was built from.

⬇ Download the latest APK: a permanent link that always points to the newest release.

Requirements

• Android 10 (API 29) or newer
• A Proton account
• A subscription: 7-day free trial, then €2.39 / month or €23.99 / year (see Subscribing below)

Install with Obtainium (recommended)

Obtainium installs and auto-updates apps straight from GitHub releases. With Obtainium already installed, tap the button to add this app in one step:

Or add it manually:

1. Install Obtainium.
2. Tap Add App and paste this repo URL: https://github.com/bolausson/sync-for-proton
3. Obtainium finds the latest release APK. Tap Install.
4. Future updates show up in Obtainium automatically.

Install from Uptodown

Also available on Uptodown, which can keep the app updated via the Uptodown app:

Install manually

1. Download the latest .apk from the Releases page.
2. Open it on your device and allow installing from this source if prompted.

Subscribing / activating

This build is paid via the web (no Google Play Billing):

1. Subscribe at https://apps.olausson.de/sync_provider_for_proton/checkout.html (monthly or yearly; 7-day free trial).
2. After payment, the page shows your subscription ID (starts with sub_). Copy it.
3. In the app, open Settings and tap the subscription button (Start 7-day free trial, or Renew after a subscription ended), paste the ID and tap Activate.
4. Keep the subscription ID somewhere safe, such as a password manager. You'll need it to re-activate after reinstalling or on another device.

Manage or cancel anytime via the link in your Paddle receipt email.

Updates & signing

APKs are signed with a stable key, and Android installs an update only if it carries the same signature; Obtainium picks up new releases from this repository. This build uses a different signing key than the Google Play version, so you can't switch between the two without uninstalling first.

Source code

The source is published from version 2.0.0 on. From then, each release tag points at the commit holding that release's source; tags of earlier releases point at commits that hold only a README. To compare, check out the tag of the version you have installed: git checkout v<version>.

This repository is generated from the development repository at each release, so pull requests cannot be merged here. Please report problems as issues instead.

Building from source

You need a JDK to start the Gradle wrapper, and the Android SDK; the command-line tools are enough once you have accepted their licences (sdkmanager --licenses). On the first run Gradle downloads itself, the JetBrains JDK 21 it builds with, the SDK platform and build tools it needs, NDK 27.3.13750724 (a large download, used to strip the prebuilt native library), and the libraries.

1. Point Gradle at your SDK, either with the ANDROID_HOME environment variable or with a local.properties file containing sdk.dir=/path/to/Android/Sdk.
2. Build a debug APK of the version sold outside Google Play: ./gradlew assembleDirectDebug (on Windows: gradlew.bat assembleDirectDebug). The APK lands in app/build/outputs/apk/direct/debug/.
3. Run the unit tests with ./gradlew testDirectDebugUnitTest. Seven time-zone tests stand in for a phone with outdated rules, so they need the JDK's time-zone data to predate 2026d (JetBrains JDK 21.0.10 has 2025b); on a JDK with newer data they are skipped.

Release builds (assembleDirectRelease) come out unsigned, because the signing key is not part of this repository. A build you make yourself is signed with a different key from the published APK, so Android treats it as a different app and it cannot update an installed copy.

OpenPGP runs in GopenPGP, a Go library, through a small binding that the build uses as the prebuilt app/libs/gopenpgpbridge.aar. The binding's source and build script are in native/gopenpgp-bridge/; GopenPGP and its dependencies are fetched at the versions its go.mod pins.

Licence

The source is available under the PolyForm Shield License 1.0.0. You may read, build, change and use it for any purpose except providing a product that competes with it, or with another product its licensor provides using it; the licence text decides. It is not an open-source licence.

Third-party components keep their own licences: see THIRD-PARTY-NOTICES.md.

Links

• Website: https://apps.olausson.de
• Privacy policy: https://apps.olausson.de/privacy-policy.txt