Signal is an encrypted messaging service intended for use in communication methods such as images, text, videos and voice. These methods may be used for both one-on-one and group communications. While most countries have access to Signal, usage is highly concentrated in only a few countries at this time.
Signal Foundation is a non-profit organization that initially released Signal in 2014. It obtained financing for the further development of Signal in 2018 by receiving initial funding of $50 million from Brian Acton. The application had been downloaded over 105 million times as of May 2021. The Signal platform had about 40 million active users as of January 2022.
Signal is a cross-platform application with a centralized architecture that's distributed as free and open-source software, such that its clients, desktop and server are all published under the AGPL-3.0-only license. The Android app is typically sold through Google Play Services, although users can purchase it elsewhere. Signal is also distributed as an iOS app as well as desktop operating systems (OSs) like Linux, macOS and Windows.
Users must register Signal with a mobile device and to identify themselves with a mobile telephone number, even for desktop versions. The software also allows users to independently verify their contacts and their data channel's integrity.
Signal uses highly effective encryption, creating concerns in countries with strict security on internet usage. For example, Egypt blocked access to Signal in December 2016. Developers added domain fronting to Signal's services in response, allowing users make their communications appear to be connecting to some other internet-based service. As a result, Signal users are able to circumvent their government's attempts to censor their communications.
Signal's domain fronting capability is enabled by default in the following countries as of May 2022:
This feature uses the Google App Engine (GAE) service, which doesn't work in Iran because Google has blocked access to GAE in Iran to comply with U.S. sanctions for that country. Iran blocked access to Signal to Iran in January 2018, prompting Signal to switch to Amazon CloudFront for domain fronting. However, Amazon announced shortly thereafter that it would prevent their services from performing domain forwarding. Signal then switched back to Google for domain forwarding in April 2019 and announced that it would begin researching new methods for enabling domain forwarding. China also blocked Signal in March 2021.
The following table shows the top five countries in terms of Signal usage, with figures indicating relative website traffic: