Signal (software)

Signal is an open-source, encrypted messaging service for instant messaging, voice calls, and video calls. The instant messaging function includes sending text, voice notes, images, videos, and other files. Communication may be one-to-one between users or may involve group messaging. The application uses a centralized computing architecture and is cross-platform software. It is developed by the nonprofit Signal Foundation and its subsidiary Signal Messenger LLC. Signal's software is free and open-source. Its mobile clients, desktop client, and server are all published under the AGPL-3.0-only license. The official Android app generally uses the proprietary Google Play Services, although it is designed to be able to work without them. Signal is also distributed for iOS and desktop programs for Windows, macOS, and Linux. Registration for desktop use requires an iOS or Android device. Signal uses mobile telephone numbers to register and manage user accounts, though configurable usernames were added in March 2024 to allow users to hide their phone numbers from other users. After removing support for SMS on Android in 2023, the app now secures all communications with end-to-end encryption. The client software includes mechanisms by which users can independently verify their contacts' identities and the data channel's integrity. The nonprofit Signal Foundation was launched in February 2018 with initial funding of $50 million from WhatsApp co-founder Brian Acton. As of January 2025, the platform had approximately 70 million monthly active users. As of January 2025, it had been downloaded more than 220 million times.