Signal is an instant messaging application and allows you to make encrypted voice calls. The app is available for Android and iOS platforms, as well as having a Chrome browser extension. Signal is a free and open sourcesoftware, developed by Open Whisper Systems and is released under GPL v3 license.
The app leverages end-to-end encryption protocols to secure all communication between users. Signal can be used to send and receive private messages, group messages, attachments, and multimedia messages. Users can independently verify the identity of their correspondents by comparing “keys”. Theapplication also allows you to send SMS and MMS.  During calls, users can check the integrity of the data channel by checking whether two words have been answered by both people in communication.
In October 2014, the Electronic Frontier Foundation (EFF) added Signal in its updated self-defense surveillance guidance.  Edward Snowden claimed to use this app.
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