SMS Tech   github.com/gitubpatrice/sms_tech

A modern, private SMS & MMS app for Android — built with Kotlin, Jetpack Compose and Material 3. No ads, no trackers, no analytics. Apache-2.0 licensed.

Status: v1.0.0 — first public release.

✨ Features

• Default SMS / MMS app for Android (KitKat → Android 14+).
• Single-Activity Compose UI, Material 3 with dynamic colors + AMOLED true-black.
• Encrypted Room database (SQLCipher), AndroidKeyStore-wrapped master key.
• App lock: PIN with PBKDF2-HMAC-SHA512, monotonic exponential backoff after failed attempts.
• Optional panic-decoy PIN: when entered, the app opens in a session where the vault (a UI-level folder of hidden conversations) is fully invisible — neither its top-bar entry point nor its rows / messages are reachable, even via saved nav state or share-target deep links. Note: the vault is currently a logical UX boundary inside the (already-encrypted by SQLCipher) Room database, not a separately-keyed cryptographic envelope. A second-layer vault crypto keyed by an setUserAuthenticationRequired = true Keystore alias is planned for v1.1.1 — see SECURITY.md for the threat model and the explicit limit.
• Inline reply & mark-as-read actions on notifications, per-conversation overrides.
• Voice SMS — on-device dictation via SpeechRecognizer (no network).
• PDF export of any conversation, generated locally via PdfDocument (no external lib).
• Scheduled sending via WorkManager (exact alarms when granted).
• Backup & restore in .smsbk (AES-256-GCM + PBKDF2) and XML SMS-Backup-Restore compat.
• Migration assistant: read the system SMS provider once SMS Tech is the default app.
• Bilingual UI: English & French, switchable at runtime.
• F-Droid friendly: no Google libraries, no proprietary blobs.

📦 Build

./gradlew assembleDebug          # → app/build/outputs/apk/debug/*.apk
./gradlew test detekt ktlintCheck lintDebug

Requires JDK 17. Min SDK 26 (Android 8.0). Compile/Target SDK 35.

🏗️ Architecture

core/      Result, AppError, crypto (AES-GCM + Keystore + PBKDF2), Timber wrapper
data/      Room (entities, DAOs, FTS4), DataStore, ContentResolver wrappers, repositories
domain/    Immutable models, repository interfaces, UseCases
system/    Receivers (SMS_DELIVER, WAP_PUSH, sent/delivered, boot), Services
           (HeadlessSmsSendService), Notifications (channels, MessagingStyle, inline reply),
           Schedulers (WorkManager)
security/  AppLockManager, AutoLockObserver (ProcessLifecycleOwner), VaultManager, PanicService
ui/        Theme (M3, dynamic, AMOLED), Navigation (type-safe), Screens (Compose), ViewModels

See ARCHITECTURE.md for the full picture and the end-to-end flow of a received SMS.

🔐 Privacy

We collect nothing. No analytics, no crash reporting, no remote logging. The only network calls SMS Tech can make are MMS transport via your carrier MMSC (INTERNET permission), and only when you actually send / receive an MMS.

SMS is not end-to-end encrypted at the protocol level — this is a limitation of the carrier network, not a choice. SMS Tech protects what's stored on your device, with SQLCipher + the AndroidKeyStore. For true end-to-end encryption, use Signal or Matrix.

See PRIVACY.md and PERMISSIONS.md.

📃 License

Apache License 2.0 — see LICENSE. © 2026 Patrice Haltaya.