Offline 36

During major socio-political events and civic disruptions—such as the July Movement in Bangladesh—students, volunteers, civil society groups, and ground activists faced severe operational hurdles in communication, resource allocation, and continuous data verification. Rapidly shifting situations require real-time coordination, transparent reporting, and lightweight, decentralized tools that remain functional even under low bandwidth or constrained technical environments. Ordinary citizens and field coordinators often struggle with fragmented information, slow-loading applications, and tools that lack continuous offline-first workflow capabilities. Without efficient, low-overhead digital systems to handle rapid estimations, data collection, and sequential monitoring, grassroots initiatives and student-led organizers lose precious time when swift decision-making and continuous operational feedback matter most.

Offline 36 is an offline-first communication system engineered to maintain uninterrupted local connectivity during internet blackouts. Built to address the communication shutdown experienced during Bangladesh’s July Movement, Offline 36 bypasses centralized network infrastructure by combining low-energy mesh protocols, direct peer-to-peer links, and cellular SMS fallback. Key Technical Pillars SOSBlue BLE Mesh Networking: Utilizes the custom SOSBlue protocol leveraging Bluetooth Low Energy (BLE). It forms a dynamic, multi-hop mesh network that relays messages across nearby devices without requiring internet access, router infrastructure, or manual device pairing. F2P (Friend-to-Friend / Peer-to-Peer) Direct Channels: Establishes encrypted direct-link connections between trusted pairs. F2P allows high-priority point-to-point updates, group broadcasts, and direct status checks within line-of-sight distance with near-zero latency. Automated SMS Fallback Routing: When target nodes extend beyond local Bluetooth reach, Offline 36 automatically bridges messages to standard SMS channels. This ensures vital alerts reach their destination even if only basic cellular coverage is available. Zero-Server Architecture & Privacy: Operates entirely without centralized servers, user accounts, or external tracking. Messages are processed and stored strictly on local device storage, preserving user privacy in high-risk environments. How It Works Node Discovery & Link Setup: Upon launch, Offline 36 scans the local environment for active BLE radio signals using SOSBlue. It establishes peer-to-peer (F2P) links with neighboring devices to join the local mesh. Message Routing & Mesh Relay: When a user sends an emergency alert or status update, the system encrypts the payload and relays it hop-by-hop across nearby SOSBlue nodes to extend communication coverage far beyond standard Bluetooth range. Failover to SMS: If no active BLE mesh path is detected for distant contacts, Offline 36 seamlessly routes the payload as an SMS text message, providing a final layer of connectivity.

Language: Java 11 (Pure Android SDK, no C/C++ or NDK) Mesh Transport: UDP Broadcast (DatagramSocket) + Wi-Fi Direct (WifiP2pManager) Encryption: AES-256-GCM with SHA-256 phone-derived keys (MessageEncryptor.java); ECDH (secp256r1) engine crypto SMS Fallback: SmsManager (Cellular SMS send/receive with runtime permissions) Persistence & Storage: SharedPreferences + In-memory ConcurrentHashMap (no SQLite); MediaStore API for local media handling Notifications: NotificationCompat (MessagingStyle with Chat and News channels)

* PUKU Editor * Freebuff * GitHub Copilot * Google Gemini