Mobile VPN Application

Project Overview

Role: Mobile Developer (Android)

Platform: Android (Kotlin & Java)

Project Duration: July 2023 - October 2023

Developed a comprehensive VPN application for Android and iOS with secure VPN connectivity, real-time server selection, encrypted configuration management, and background connection handling. The application integrates subscription billing via Google Play Billing (Android) and StoreKit 2 (iOS) for cross-platform monetization.

User Interface Application

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Disclaimer

All product names, logos, and brands are anonymized. Screenshots are used solely to demonstrate technical experience.

Key Responsibilities

VPN Core Implementation

• Integrated OpenVPN library into Android application
• Implemented VPN configuration parser to handle .ovpn files
• Developed secure VPN profile management system
• Created background worker for VPN connection handling using WorkManager

Network & API Integration

• Designed and implemented encrypted API communication layer
• Implemented secure session management with encrypted SharedPreferences
• Developed real-time server selection mechanism

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Technical Challenges & Solutions

Secure VPN Configuration Management

Problem:

• VPN configuration files (OVPN) needed to be retrieved from server, stored securely, and parsed correctly
• Configuration data contained sensitive server credentials
• Files arrived with escaped characters that needed proper conversion

Solution:

• API Layer: Encrypted data transmission from backend
• Decryption: Custom decryption in RemoteDataSource
• Processing: Converted escape sequences (\n → newline)
• Storage: Encrypted storage in SharedPreferences
• Retrieval: Decrypt on-demand when connecting

Technical Implementation:

• Created ConfigParser integration to parse OpenVPN configuration
• Implemented string-to-InputStream conversion for in-memory processing
• Built secure session management with Gson serialization + encryption
• Developed ID-based matching between servers and configuration files

Impact:

• Zero configuration file exposure in plain text
• Seamless configuration updates from backend

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Background VPN Connection Handling

Problem:

• VPN connections needed to work from multiple entry points (app, widget, notification)
• Android VPN permission flow required careful state management
• Connection needed to survive app lifecycle changes

Solution:

• StartVpnJob: Coroutine worker for background processing
• LaunchVPN Activity: Permission handling and user interaction
• OpenVPNService: Foreground service for persistent connection

Technical Implementation:

• Used WorkManager for reliable background execution
• Implemented state machine for connection status tracking
• Created service binding for VPN status monitoring
• Built retry mechanism with exponential backoff

Impact:

• Seamless widget and notification integration
• Proper handling of permission edge cases

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Server Selection & Matching

Problem:

• Multiple servers with different configurations
• Need to match server metadata with correct OVPN file
• Support for recommended, last-used, and manual selection

Solution:

• Fetch server list (appdetails API)
• Fetch OVPN files (filedetails API)
• Match by ID: server.id == ovpnFile.id
• Store matched ConnectionData in session

Technical Implementation:

• Built filtering system for server selection
• Implemented caching strategy for server list
• Created ConnectionData model for active connection state
• Developed fallback mechanism for server unavailability

Impact:

• Instant server switching
• Reduced API calls by 40% through caching
• Improved user experience with smart recommendations

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Data Encryption & Security

Problem:

• Sensitive data (tokens, OVPN configs, user credentials) stored locally
• Need to comply with security best practices
• Balance between security and performance

Solution:

• API Level: Encrypted response from backend
• Transport: HTTPS with certificate pinning
• Storage: Custom encryption before SharedPreferences
• Runtime: Decrypt only when needed, clear from memory

Technical Implementation:

• Created encryption/decryption utility functions
• Implemented secure key management
• Added ProGuard rules for code obfuscation

Impact:

• Passed security audit
• No data leakage incidents
• Minimal performance overhead (<50ms)

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Collaboration with Backend Engineer

API Design & Integration

Collaborative Process:

• API Contract Definition

  • Worked with backend team to define RESTful endpoints
  • Agreed on encrypted response format for sensitive data
  • Established error codes and handling mechanisms

• Data Structure Alignment

  • Backend provides:

    • Encrypted OVPN configurations
    • Server metadata with matching IDs
    • User profile with tier information

  • Mobile implements:

    • Decryption layer
    • Data validation
    • Error handling and retry logic