On 24 February 2014, Open Whisper Systems introduced TextSecure v2, which migrated to the Axolotl Ratchet. The first version of the protocol, TextSecure v1, was based on Off-the-Record Messaging (OTR). The Signal Protocol's development was started by Trevor Perrin and Moxie Marlinspike (Open Whisper Systems) in 2013. The protocol combines the Double Ratchet algorithm, prekeys, and a triple Elliptic-curve Diffie–Hellman (3-DH) handshake, and uses Curve25519, AES-256, and HMAC-SHA256 as primitives. Facebook Messenger also say they offer the protocol for optional Secret Conversations, as does Skype for its Private Conversations. Several closed-source applications have implemented the protocol, such as WhatsApp, which is said to encrypt the conversations of 'more than a billion people worldwide' or Google who provides end-to-end encryption by default to all RCS-based conversations between users of their Messages app for one-to-one conversations. The protocol was developed by Open Whisper Systems in 2013 and was first introduced in the open-source TextSecure app, which later became Signal. The Signal Protocol (formerly known as the TextSecure Protocol) is a non- federated cryptographic protocol that can be used to provide end-to-end encryption for voice calls and instant messaging conversations. Non-federated cryptographic protocol Signal Protocol Communication protocol

Signal instant messenger