Where

A cross-platform, end-to-end encrypted real-time location sharing app for iOS and Android, built with Kotlin Multiplatform.

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Links

• Webpage: where.af0.net
• Android: Google Play
• iOS: App Store
• Beta Testing: Join the closed testing group

Screenshots

Privacy model

Where is designed so the server learns as little as possible:

• No accounts. Identity is a device-scoped ephemeral X25519 key pair — no usernames, email addresses, or persistent IDs.
• End-to-end encrypted by default. Location payloads are encrypted with a Double Ratchet protocol before they leave the device. The server routes opaque ciphertext and cannot read coordinates.
• No social graph. Routing uses pairwise anonymous tokens; the server cannot reconstruct who is sharing with whom.
• Forward secrecy. Automated keepalives advance the ratchet even when only one party is sharing, so past sessions cannot be decrypted if a key is later compromised.

Architecture

[iOS / Android]
  GPS → LocationService
      → encrypt (Double Ratchet)
      → POST /inbox/{send_token}

[Server]
  routes opaque ciphertext, no decryption

[Recipient]
  GET /inbox/{recv_token}
      → decrypt
      → update map pin

Module	Description
shared/	KMP library — data models, Double Ratchet E2EE, LocationClient
android/	Android app — Jetpack Compose UI, FusedLocation foreground service, Google Maps
ios/	iOS app — SwiftUI, MapKit, CoreLocation
server/	Ktor server — Anonymous Mailbox API, DynamoDB-backed message store
cli/	Command-line tool for scripting and testing

Getting started

Server

Uses an in-memory store by default; set AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY and AWS_REGION to use DynamoDB.

./gradlew :server:run
curl localhost:8080/health   # → ok

Android

1. Add your keys to local.properties:

   MAPS_API_KEY=your_google_maps_key
   SERVER_HTTP_URL=http://10.0.2.2:8080   # emulator; use LAN IP for a real device
   

2. Build and install:

   ./gradlew :android:assembleDebug
   

iOS

1. Generate the Xcode project:

   cd ios && xcodegen generate
   

2. Open ios/Where.xcodeproj in Xcode and run on simulator or device.
   • The KMP shared framework is built automatically as a pre-build step.
   • Debug builds on the simulator talk to a local server (./scripts/run-server.sh); other builds use production. Override with WHERE_SERVER_HTTP_URL in the Xcode scheme (see ios/Sources/Where/ServerConfig.swift).

CLI

Useful for scripting, integration testing, and pairing two terminals to verify the protocol end-to-end.

./gradlew :cli:installDist

# Terminal A — create an invite
./cli/build/install/cli/bin/cli init
./cli/build/install/cli/bin/cli invite          # prints a where.af0.net/invite#… URL

# Terminal B — accept and start syncing
./cli/build/install/cli/bin/cli join <url> bob
./cli/build/install/cli/bin/cli sync

See MANUAL_TESTING.md for a full walkthrough.

Development

Running tests

./gradlew :shared:jvmTest

The E2EE crypto tests live in shared/src/commonTest/kotlin/net/af0/where/e2ee/.

Local configuration

Machine-specific paths go in gitignored local files — never in checked-in config:

File	Purpose
local.properties	Android SDK path, Maps API key, server URL
local.gradle.kts	Build output dirs, cache dirs, SDK locations
.envrc	Environment variables (GRADLE_USER_HOME, KONAN_DATA_DIR, etc.)

Protocol documentation

See E2EE location sync design

License

MIT