Signal is a
cross-platform
In computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several computing platforms. Some cross-platform software ...
centralized
Centralisation or centralization (see spelling differences) is the process by which the activities of an organisation, particularly those regarding planning and decision-making, framing strategy and policies become concentrated within a particu ...
encrypted instant messaging
Instant messaging (IM) technology is a type of online chat allowing real-time text transmission over the Internet or another computer network. Messages are typically transmitted between two or more parties, when each user inputs text and tri ...
service developed by the non-profit
Signal Foundation and its subsidiary, the
Signal Messenger LLC. Users can send one-to-one and group messages, which can include
files, voice notes,
images and
videos
Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) system ...
.
It can also be used to make one-to-one and group
voice
The human voice consists of sound made by a human being using the vocal tract, including talking, singing, laughing, crying, screaming, shouting, humming or yelling. The human voice frequency is specifically a part of human sound producti ...
and
video calls.
The
Android version also optionally functions as an
SMS
Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text ...
app, but this functionality will be removed in 2023.
Signal uses standard cellular
telephone number
A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices f ...
s as identifiers and secures all communications to other Signal users with
end-to-end encryption. The client software includes mechanisms by which users can independently verify the identity of their contacts and the integrity of the data channel.
Signal's software is
free and open-source
Free and open-source software (FOSS) is a term used to refer to groups of software consisting of both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the source ...
. Its
mobile clients are published under the
GPL-3.0-only license
A license (or licence) is an official permission or permit to do, use, or own something (as well as the document of that permission or permit).
A license is granted by a party (licensor) to another party (licensee) as an element of an agreeme ...
,
while the
desktop client and
server
Server may refer to:
Computing
*Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients
Role
* Waiting staff, those who work at a restaurant or a bar attending customers and su ...
are published under the
AGPL-3.0-only license.
The official Android app generally uses the proprietary
Google Play Services (installed on most Android devices), though it is designed to still work without them installed. Signal also has an official client app for
iOS and desktop programs for
Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...
,
macOS
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
and
Linux
Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
(although registration requires an iOS or Android device).
The
non-profit
A nonprofit organization (NPO) or non-profit organisation, also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collective, public or social benefit, in co ...
Signal Foundation was launched in February 2018 with initial funding of $50 million from
Brian Acton
Brian Acton (born 1972/1973) is an American computer programmer and Internet entrepreneur. Acton is the executive chairman of the Signal Technology Foundation, which he co-founded with Moxie Marlinspike in 2018. , Acton also serves as interim ...
.
, the platform had approximately 40 million monthly active users. , it was downloaded more than 105 million times.
History
2010–2013: Origins
Signal is the successor of the RedPhone encrypted voice calling app and the
TextSecure
TextSecure was an encrypted messaging application for Android that was developed from 2010 to 2015. It was a predecessor to Signal and the first application to use the Signal Protocol, which has since been implemented into WhatsApp and other a ...
encrypted texting program. The
beta versions of RedPhone and TextSecure were first launched in May 2010 by
Whisper Systems
Whisper Systems was an American enterprise mobile security company that was co-founded by security researcher Moxie Marlinspike and roboticist Stuart Anderson in 2010. The company was acquired by Twitter in November 2011. Some of the company's ...
,
a startup company co-founded by security researcher
Moxie Marlinspike and roboticist Stuart Anderson.
Whisper Systems also produced a firewall and tools for encrypting other forms of data.
All of these were