BurnerPad

Encrypted. Plain. Private.

BurnerPad is an open-source, plain-text notepad for Android with no ads, no cloud, no tracking, and no formatting. Your notes are encrypted on your device and unreadable without your PIN — even to us.

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Features

• PIN-protected — PBKDF2-derived encryption key, minimum 5 characters
• Duress PIN — a second PIN that silently wipes all notes and opens a blank app
• Double encryption — Android Keystore outer layer + AES-256-CBC inner layer
• No cloud — notes never leave your device
• No formatting — plain text only, rich formatting stripped on paste
• Autosave — optional; off by default, with shadow/recovery copies when disabled
• Status bar — optional word and character count footer in the editor
• Folders — organize notes into subdirectories
• Import / Export — plaintext files via Android SAF; exports go to Downloads
• Backup / Restore — encrypted archive (AES-256-CBC, PBKDF2-derived key, 12+ char password) saved to Downloads; compatible with archives from the original React Native version
• No-PIN mode — set PIN to 12345 to skip the lock screen silently
• Themes — dark, light, and system-default

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Security Architecture

BurnerPad uses a two-layer encryption model:

Outer layer — Android Keystore Managed by EncryptedSharedPreferences. Key material is stored in the Android Keystore, tied to the app's package name and signing certificate. This layer protects against extraction of key material from the device filesystem.

Inner layer — AES-256-CBC + HMAC-SHA256 Each note is encrypted with a key derived from the user's PIN using PBKDF2WithHmacSHA256 (100,000 iterations, 128-bit random salt per installation). Authentication is provided by HMAC-SHA256 over the ciphertext. This layer protects notes even if the outer layer is bypassed.

Key derivation — CryptoManager.java All cryptographic operations (PBKDF2, AES-256-CBC, HMAC-SHA256, secure random) are implemented in javax.crypto exclusively. No third-party crypto libraries.

Session key The PIN-derived session key is held in memory only. It is never written to disk. It is cleared when the app goes to the background, requiring PIN re-entry on return.

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Building

BurnerPad is a native Android Java app. It is built using a remote build server that pulls from GitHub, scaffolds the Gradle project, and returns signed artifacts.

Prerequisites

• x86-64 Linux build host (AAPT2 is x86-64 only — ARM build hosts are not supported)
• Python 3
• Java 17 (JAVA_HOME must point to JDK 17)
• Android SDK with platform-tools, android-36, and build-tools/36.0.0 (ANDROID_HOME must be set)
• imagemagick (sudo apt install imagemagick) for icon density generation

Build

Push your changes to GitHub, then trigger a build:

python3 build_server.py --repo BurnerPad

Add --clean to force a full scaffold rebuild (required after dependency changes or when files are deleted).

Artifacts are produced at:

• BurnerPad-<version>.apk — unsigned release APK
• BurnerPad-<version>-signed.apk — debug-signed APK for sideload testing
• BurnerPad-<version>.aab — Android App Bundle for Play Store upload

The generated scaffold directory is outside the repo in ~/build_server/workspace/ and is never committed.

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Repository Structure

BurnerPad/
├── build.json                    # Build configuration (version, SDK, dependencies)
├── icon-512.png                  # Source icon (512×512, generates all density variants)
├── docs/
│   └── privacy.html              # Privacy policy (served via GitHub Pages)
└── app/src/main/
    ├── AndroidManifest.xml
    ├── java/com/github/zaegan/burnerpad/
    │   ├── MainActivity.java         # Cold-start router
    │   ├── PinActivity.java          # Lock screen
    │   ├── OnboardingActivity.java   # First-launch PIN setup
    │   ├── WalkthroughActivity.java  # Post-setup feature walkthrough
    │   ├── FileBrowserActivity.java  # Note and folder browser
    │   ├── EditorActivity.java       # Plain text editor with autosave
    │   ├── SettingsActivity.java     # Settings (theme, autosave, PIN, backup, duress)
    │   ├── BurnerPadApp.java         # Application class, background lock management
    │   ├── crypto/
    │   │   └── CryptoManager.java    # PBKDF2, AES-256-CBC, HMAC-SHA256, session key
    │   ├── storage/
    │   │   └── StorageManager.java   # Note CRUD, shadow/recovery, archive backup/restore
    │   ├── prefs/
    │   │   ├── PinManager.java       # PIN lifecycle, preferences
    │   │   └── SecurePrefs.java      # EncryptedSharedPreferences wrapper
    │   ├── theme/
    │   │   └── ThemeManager.java     # Theme application (dark/light/system)
    │   └── tutorial/
    │       └── TutorialManager.java  # In-app tutorial state and dismissal
    └── res/
        ├── layout/                   # Activity layouts
        ├── values/                   # Light theme colors, strings, attrs
        └── values-night/             # Dark theme colors

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Important Warnings

• There is no PIN recovery. If you forget your PIN, a full reinstall is the only option and it destroys all notes.
• The duress PIN permanently wipes all notes when entered. There is no undo.
• Backup archives are encrypted. If you forget the archive password, the backup is unrecoverable.

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License

MIT