Themis is a cross-platform cryptographic library developed by Cossack Labs, providing high-level security primitives such as Secure Cell (symmetric encryption with three modes: Seal, Token Protect, Context Imprint), Secure Message (asymmetric encryption and digital signing), Secure Session (mutual authentication and key exchange), Secure Comparator (zero-knowledge password comparison), and key generation (EC, RSA, symmetric). The core is implemented in C with a cryptographic engine abstraction layer (Soter) that supports OpenSSL, BoringSSL, and a custom Ed25519 implementation. The library exposes consistent APIs across 13+ language wrappers including Python, Go, Rust, Java, Swift, Objective-C, JavaScript (Node.js and WebAssembly), PHP, Ruby, C++, and React Native. The codebase is well-structured with extensive unit, integration, and fuzz testing, CI/CD pipelines for each wrapper, and cross-language compatibility tests. While the repository has deprecated older APIs and maintains multiple backends, it remains actively maintained with regular releases, security patches, and community engagement.
Threema Android is a secure messaging application with end-to-end encryption using NaCl/libsodium. It features a modular architecture following clean architecture principles with separation into app, domain, data, and common layers. The app uses MVVM with ViewModels and StateFlow/LiveData, dependency injection via Koin, and Kotlin coroutines for asynchronous operations. Key functionality includes text/media messaging, voice/video calls, group chats, polls, contact management, backup/restore, multi-device synchronization, and availability status indicators. The application supports multiple build variants for different distribution channels (Google Play, Huawei AppGallery, F-Droid, Threema Shop) and includes enterprise features for business users. It relies on SQLCipher for encrypted local storage, implements custom CSP/D2M protocols for server communication, and provides web client functionality for desktop access.