Astraea

A private, offline-first calendar with optional end-to-end encrypted sync over Nostr.

About

Astraea keeps the network optional. Events, recurrences, reminders, calendar views, widgets, imports and exports work locally without an account. Users who want multi-device synchronization can connect a Nostr identity and explicitly choose the relays that will store their encrypted calendar.

Calendar contents are NIP-44 self-encrypted before publication. Relay operators can observe protocol metadata such as the public key, IP address, timestamps and event sizes, but cannot read event titles, descriptions, locations or reminder details.

Features

• Offline-first calendar with month, week, day and upcoming-list views.
• Recurring events with daily, weekly, monthly and yearly presets.
• Local reminders scheduled by the operating system, including recurring occurrences and reboot restoration on Android.
• Optional Nostr sync using encrypted kind 30078 parameterized-replaceable events and NIP-09 deletion requests.
• Flexible identity through an imported key, a locally generated account or the Amber NIP-55 external signer on Android.
• Explicit relay choice during onboarding and in Settings. nos.lol and relay.damus.io are suggestions, not mandatory infrastructure.
• Personal relay support as an additional backup destination.
• Encrypted exports using PBKDF2-HMAC-SHA256 and AES-256-GCM, alongside standard unencrypted iCalendar (.ics) import/export.
• Android home-screen widgets for daily, weekly and monthly agendas.
• Timezone-aware storage: instants are stored in UTC and rendered in the selected or device timezone.
• Light and dark themes, with dark mode as the privacy-oriented default.

How synchronization works

1. Every mutation is written to the local Hive store first.
2. When sync is enabled, the event JSON is encrypted to the user's own Nostr identity with NIP-44.
3. Astraea signs and publishes a kind 30078 event under a stable d tag.
4. Each configured relay must acknowledge the publication before the local version is marked as synchronized.
5. Pulls verify the NIP-01 event ID and Schnorr signature, decrypt valid events, then merge them using the latest updatedAt timestamp.
6. Deletions publish both an encrypted tombstone and a NIP-09 request so other devices can learn the deletion even when a relay ignores retractions.

No Astraea server, account service or analytics backend sits in this path.

Platform status

Platform	Status	Notes
Android	Supported	Primary audited target; Amber and home-screen widgets available.
Web	Experimental	Builds are scaffolded, but sensitive production use needs a browser/CSP review.
iOS	Not configured	Platform project and release hardening are not included yet.
Desktop	Not configured	No packaged desktop targets yet.

Getting started

Requirements

• Flutter stable with Dart 3.12.2 or newer
• JDK 17
• Android SDK 36 for Android builds
• A configured device or emulator

Check the local toolchain, install locked dependencies and run Astraea:

flutter doctor
flutter pub get --enforce-lockfile
flutter run

Quality checks

dart format --output=none --set-exit-if-changed lib test
bash tool/check_repository_hygiene.sh
flutter analyze
flutter test
flutter build apk --debug

The test suite covers NIP-44 official vectors, iCalendar round trips, recurrence expansion, relay settings and the first-launch onboarding flow.

Project structure

lib/
  models/       Calendar, account, profile and settings data
  providers/    Riverpod state and application orchestration
  screens/      Calendar, editor, onboarding and settings UI
  services/     Storage, Nostr, sync, notifications, widgets and exports
  utils/        NIP-44, recurrence, iCalendar, formatting and validation
android/        Android host app and native home-screen widgets
test/           Unit, crypto-vector and widget tests
web/            Experimental Flutter web shell
docs/           Architecture, release notes and security audit

Release builds

Release builds intentionally fail unless a dedicated keystore is configured; the project never falls back to Android's debug signing identity. See Releasing for the complete checklist.

Never commit android/key.properties, a keystore, private Nostr keys, service credentials or local environment files. The repository ignore rules cover the common variants, but release operators remain responsible for reviewing every staged change.

Documentation

• Architecture
• Privacy policy
• Security policy
• Security audit
• Contributing
• Changelog

Contributing

Bug reports and focused pull requests are welcome. Please read CONTRIBUTING.md and run the full quality checks before opening a pull request. Security vulnerabilities must follow the private process in SECURITY.md, not a public issue.

Acknowledgements

Astraea is part of the Echoes ecosystem and is built on open protocols and open-source projects including Flutter, Nostr, Riverpod, Hive, Amber and dart_nostr.

License

Copyright holders license Astraea under the GNU General Public License v3.0 or later.