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 r ...
centralized encrypted
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can deci ...
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 trigge ...
service developed by the non-profit
Signal Foundation
The Signal Foundation, officially the Signal Technology Foundation, is an American non-profit organization founded in 2018 by Moxie Marlinspike and Brian Acton. Its mission is "to develop open-source privacy technology that protects free expres ...
and its subsidiary, the
Signal Messenger LLC. Users can send one-to-one and group messages, which can include
files, voice notes,
images
An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...
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) syste ...
.
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 production in ...
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
End-to-end encryption (E2EE) is a system of communication where only the communicating users can read the messages. In principle, it prevents potential eavesdroppers – including telecommunications service providers, telecom providers, Internet ...
. 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
Mobile may refer to:
Places
* Mobile, Alabama, a U.S. port city
* Mobile County, Alabama
* Mobile, Arizona, a small town near Phoenix, U.S.
* Mobile, Newfoundland and Labrador
Arts, entertainment, and media Music Groups and labels
* 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
A desktop traditionally refers to:
* The surface of a desk (often to distinguish office appliances that fit on a desk, such as photocopiers and printers, from larger equipment covering its own area on the floor)
Desktop may refer to various compu ...
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
Google Play Services is a proprietary software package produced by Google for installation on Android devices. It consists of background services and libraries for use by mobile apps running on the device When it was introduced in 2012, it pro ...
(installed on most Android devices), though it is designed to still work without them installed. Signal also has an official client app for
iOS
iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also include ...
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 serv ...
,
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 lapt ...
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, which ...
(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.
, 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 app ...
encrypted texting program. The
beta version
A software release life cycle is the sum of the stages of development and maturity for a piece of computer software ranging from its initial development to its eventual release, and including updated versions of the released version to help impro ...
s 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 s ...
,
a startup company co-founded by security researcher
Moxie Marlinspike
Moxie Marlinspike is an American entrepreneur, cryptographer, and computer security researcher. Marlinspike is the creator of Signal, co-founder of the Signal Technology Foundation, and served as the first CEO of Signal Messenger LLC. He is als ...
and roboticist Stuart Anderson.
Whisper Systems also produced a firewall and tools for encrypting other forms of data.
All of these were