Android App

Programming Language: Signal is primarily written in Java for Android and Swift for iOS.

Encryption Library: The app relies on the Signal Protocol, which provides end-to-end encryption for secure messaging. The Signal Protocol is implemented in the Signal app to ensure the confidentiality and integrity of messages.

VoIP (Voice over Internet Protocol): For voice and video calling, Signal uses the WebRTC (Web Real-Time Communication) library. WebRTC enables real-time communication directly between web browsers and mobile applications.

Push Notifications: Signal utilizes platform-specific push notification services, such as Apple Push Notification Service (APNs) for iOS and Firebase Cloud Messaging (FCM) for Android, to notify users of new messages.

User Interface Frameworks: The app's user interface is built using the native frameworks for each platform—UIKit for iOS and Android SDK for Android.

Database: Signal uses a database to store user data and messages. On Android, it often employs SQLite, while on iOS, it might use Core Data or another storage mechanism.

Version Control: Like many software projects, Signal uses a version control system, and the code is available on GitHub. The GitHub repository allows for collaboration, issue tracking, and contributions from the open-source community.

Build Tools: For building and managing dependencies, Signal uses build tools like Gradle for Android and Xcode for iOS.

Secure Design Practices: Signal employs various secure design practices and undergoes regular security audits to maintain user privacy and security.