Signal is an open-source , encrypted messaging service for instant messaging , voice calls , and video calls. The application uses a centralized computing architecture and is cross-platform software. Signal's software is free and open-source. Its mobile clients, desktop client, and server are all published under the AGPL 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 to allow users to hide their phone numbers from other users. The client software includes mechanisms by which users can independently verify the identity of their contacts and the integrity of the data channel.
As of May [update] , it was downloaded more than million times. Signal is the successor of the RedPhone encrypted voice calling app and the TextSecure encrypted texting program. The beta versions of RedPhone and TextSecure were first launched in May by Whisper Systems , [ 54 ] a startup company co-founded by security researcher Moxie Marlinspike and roboticist Stuart Anderson.
In November , Whisper Systems announced that it had been acquired by Twitter. Neither company disclosed the financial terms of the deal. Marlinspike could help the then-startup improve its security". Open Whisper Systems' website was launched in January In February , Open Whisper Systems introduced the second version of their TextSecure Protocol now Signal Protocol , which added end-to-end encrypted group chat and instant messaging capabilities to TextSecure.
The developers said that their next steps would be to provide TextSecure instant messaging capabilities for iOS, unify the RedPhone and TextSecure applications on Android, and launch a web client. On 4 October , the American Civil Liberties Union ACLU and Open Whisper Systems published a series of documents revealing that OWS had received a subpoena requiring them to provide information associated with two phone numbers for a federal grand jury investigation in the first half of On 21 February , Moxie Marlinspike and WhatsApp co-founder Brian Acton announced the formation of the Signal Technology Foundation , a c 3 nonprofit organization whose mission is "to support, accelerate, and broaden Signal's mission of making private communication accessible and ubiquitous".
