Shredder - Secure File Deletion for Android

Shredder is a high-security Android application designed to permanently and irrecoverably delete files and directories. It implements industry-standard multi-pass shredding algorithms to thwart data recovery even from specialized hardware forensic tools.

🚀 Key Features

• Multi-Pass Shredding: Implements a robust 3-pass overwrite algorithm.
• Metadata Wiping: Renames files to random strings and truncates them before final deletion to hide original file identities.
• Free Space Wiper: Securely wipes available free space on the device storage to prevent recovery of previously deleted files.
• Nuclear Option: Integrated device administrator capability to trigger a secure factory reset (wiping all data).
• Foreground Execution: Uses Android Foreground Services to ensure long-running shredding tasks complete successfully even if the app is in the background.
• Biometric Security: Protects the entire application and high-risk operations (like the Nuclear Option) with Biometric/PIN authentication.
• Notification Support: Fully compatible with Android 13+ notification permissions for reliable foreground execution.
• Modern UI: Built entirely with Jetpack Compose for a responsive, fluid user experience, featuring a collapsible real-time console.

🛠 Technical Implementation

Shredding Algorithm (ShredderEngine.kt)

The core engine implements a 3-pass overwrite strategy:

1. Pass 1 (Random): Overwrites the entire file with cryptographically strong random data using java.security.SecureRandom.
2. Pass 2 (Pattern): Overwrites with alternating bit patterns (0xAA, 0x55) to stress test and flip bits on magnetic and flash storage cells.
3. Pass 3 (Random): A final pass of random entropy.

I/O Optimization:

• Uses RandomAccessFile in "rw" mode for direct disk access.
• Employs a 1MB buffer to maximize throughput on modern high-speed storage.
• Explicitly calls FileDescriptor.sync() after every pass to ensure the OS flushes the write buffer to physical hardware.

Service Architecture (ShredderService.kt)

Shredding is an I/O intensive and potentially long-running operation. To prevent the system from killing the process:

• The app promotes itself to a Foreground Service.
• Uses START_NOT_STICKY to manage lifecycle efficiently.
• Provides real-time progress updates via a persistent notification.

Security & Permissions

• MANAGE_EXTERNAL_STORAGE: Utilizes the Scoped Storage "All Files Access" permission (on Android 11+) to allow deep shredding across the entire user-accessible storage.
• Device Administration: Registered as a Device Admin to enable the wipeData() system call for the "Nuclear Option".
• POST_NOTIFICATIONS: Required on Android 13+ to show the foreground service notification, ensuring the shredding process is not interrupted.
• No Backups: android:allowBackup="false" is set in the Manifest to prevent sensitive app states from being cached in cloud backups.

🏗 Build Requirements

• Android SDK: 36 (target), 24 (min)
• Language: Kotlin
• UI Framework: Jetpack Compose
• Build System: Gradle Kotlin DSL (.kts)

🛡 Production Readiness

The application is configured for production with:

• R8/ProGuard: Enabled for code shrinking and obfuscation.
• Resource Shrinking: Enabled to minimize APK footprint.
• Log Sanitization: Verbose and debug logging is disabled in the core engine to prevent metadata leakage in logcat.

🆕 What's New (v1.1)

• App-wide Lock: Added biometric authentication barrier on application start.
• Refactored Architecture: Optimized MainActivity for better performance and maintainability using decomposed composables and state-driven UI.
• Kotlin Intrinsics: Migrated core math operations to kotlin.math for improved platform integration.
• Bug Fixes: Resolved resource linking issues and optimized file listing logic.

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Disclaimer: Data deleted with Shredder is IRREVERSIBLE. Use with caution.