Signal
Signal is an end-to-end encrypted messaging app run by a nonprofit organization; built on the open-source Signal Protocol, it offers text messaging, voice calls and other features, and its client and server code is publicly released.
Contents10 sections
Key facts
July 29, 2014Launch of Signal for iPhone
Open Whisper Systems released Signal for iPhone, offering free, worldwide encrypted voice calls compatible with RedPhone on Android, and said that TextSecure and RedPhone on Android would be combined into a unified Signal app.[1]
November 2, 2015Consolidation on Android
Signal for Android was released, completing the effort to combine TextSecure and RedPhone into a single app.[2]
November 4, 2016X3DH Protocol Specification
The first revision of the X3DH key agreement protocol specification published by Signal is dated November 4, 2016, with Moxie Marlinspike and Trevor Perrin (editor) as authors.[3]
February 21, 2018Formation of the Signal Foundation
Signal announced the Signal Foundation, a nonprofit created and funded by Brian Acton with an initial $50 million, with Acton as executive chairman; Moxie Marlinspike continued as CEO of the newly created Signal Messenger nonprofit organization.[4]
January 10, 2022CEO Transition
Moxie Marlinspike announced that he would step down as Signal’s CEO, with Brian Acton, also a member of the Signal Foundation board, serving as interim CEO during the search for a successor.[5]
September 19, 2023Introduction of Quantum-Resistant PQXDH
Signal announced an upgrade of X3DH to PQXDH, combining X25519 with CRYSTALS-Kyber so that an attacker must break both to obtain the shared secret.[6]
February 20, 2024Usernames and Phone Number Privacy
Signal introduced usernames, letting users start chats without sharing their phone number; phone numbers are by default no longer shown to people who do not already have them saved, and a new setting lets users stop others from finding them by number.[7]
As of October 2026: Operator and Open Source Status
Signal’s website describes it as an independent 501(c)(3) nonprofit with no ties to major tech companies; its trademarks are owned by Signal Technology Foundation. The app implements end-to-end encryption with the open-source Signal Protocol.[8]
Signal’s Android, iOS and desktop clients, its server, and the libsignal library implementing the Signal Protocol are published on GitHub under the AGPL-3.0 license.[9]
Related Organizations, Websites, and Public Accounts
Signal: Official website: https://signal.org/ (opens in a new window)[8]
X: Official account: https://x.com/signalapp (opens in a new window)[8]
GitHub: Official account: https://github.com/signalapp (opens in a new window)[8][9]
Sources
- Free, Worldwide, Encrypted Phone Calls for iPhone (opens in a new window)
- Just Signal (opens in a new window)
- The X3DH Key Agreement Protocol (opens in a new window)
- Signal Foundation (opens in a new window)
- New year, new CEO (opens in a new window)
- Quantum Resistance and the Signal Protocol (opens in a new window)
- Keep your phone number private with Signal usernames (opens in a new window)
- Signal >> Home (opens in a new window)
- Signal (opens in a new window)