signal (software)

signal (software). Signal is a cross-platform encrypted messaging service developed by the Signal Technology Foundation and Signal Messenger LLC. It uses the Internet to send one-to-one and group messages, which can include files, voice notes, images, and videos, as well as make one-to-one voice and video calls. The service is distinguished by its focus on privacy, employing end-to-end encryption for all communications by default through its proprietary Signal Protocol.

History

The origins of Signal trace back to Open Whisper Systems, a project founded by Moxie Marlinspike and Stuart Anderson. The first standalone application, Signal, was launched for iOS in 2014, following earlier encrypted communication projects like TextSecure and RedPhone. In 2018, Marlinspike and Brian Acton, co-founder of WhatsApp, established the Signal Technology Foundation as a non-profit entity to oversee development. Significant growth occurred following policy changes at rival platforms like Facebook (now Meta Platforms) and endorsements from privacy advocates such as Edward Snowden and Jack Dorsey. The 2021 WhatsApp privacy policy update prompted a major surge in Signal's user base, with millions of new registrations reported.

Features

Signal's core functionality includes text messaging, group chats, and high-definition voice and video calls. All forms of communication are protected by end-to-end encryption. Additional features include disappearing messages, view-once media, message reactions, and stories. The app supports media sharing, including documents and contacts, and allows users to customize chat wallpapers. Notably, Signal introduced Signal PINs to facilitate secure data transfer between devices without relying on cloud backups. Its Desktop applications for Linux, macOS, and Microsoft Windows operate as linked companions to a primary mobile device.

Security and privacy

Signal's security model is built upon the Signal Protocol, an open-source cryptographic library that provides end-to-end encryption for text, voice, and video. This protocol has been adopted by other major services, including WhatsApp, Facebook Messenger, and Google Messages. Signal collects minimal metadata, storing only the date of account creation and the last connection time. Messages are stored encrypted on user devices, not on Signal's servers. The app's code is open-source, subject to independent audits by organizations like Trail of Bits. Its use of Perfect Forward Secrecy and resistance to decryption via quantum computing are frequently highlighted by security researchers.

Technical details

The Signal client applications are primarily written in Java for Android, Swift for iOS, and a combination of C, C++, and Rust for core cryptographic libraries and desktop clients. Communication relies on the Internet Protocol Suite, with messages routed through Signal's servers. The service uses a centralized architecture but is designed so that the server software, also open-source, cannot compromise the encryption. Registration requires a telephone number for identity, but the company has explored alternatives like usernames to enhance privacy. The AGPLv3 license governs its open-source distribution.

Reception and impact

Signal has received widespread acclaim from the security community, with endorsements from figures like Edward Snowden and organizations such as the Electronic Frontier Foundation. It is often recommended as a gold standard for private communication by journalists, activists, and political dissidents in regions with oppressive regimes. The app has faced temporary blocks in countries like Iran and China. Its influence is evident in pushing broader industry adoption of end-to-end encryption, impacting the design of applications from Meta Platforms and Apple Inc.. Criticisms have centered on its requirement for a phone number and its centralized server infrastructure, though its non-profit model is generally viewed as aligning its incentives with user privacy.

Category:Instant messaging clients Category:Cryptographic software Category:Free software