Communication protocol | |
![]() Signal Protocol full double ratchet step. | |
Purpose | End-to-end encrypted communications |
---|---|
Developer(s) | Signal Foundation |
Based on | OTR, SCIMP[1] |
Influenced | OMEMO, Matrix[2] |
OSI layer | Application layer |
Website | signal |
The Signal Protocol (formerly known as the TextSecure Protocol) is a non-federated cryptographic protocol that provides end-to-end encryption for voice and instant messaging conversations.[2] The protocol was developed by Open Whisper Systems in 2013[2] and was introduced in the open-source TextSecure app, which later became Signal. 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"[3] or Google who provides end-to-end encryption by default to all RCS-based conversations between users of their Google Messages app for one-to-one conversations.[4] Facebook Messenger also say they offer the protocol for optional Secret Conversations, as does Skype for its Private Conversations.
The protocol combines the Double Ratchet Algorithm, prekeys, and a triple Elliptic-curve Diffie–Hellman (3-DH) handshake,[5] and uses Curve25519, AES-256, and HMAC-SHA256 as primitives.[6]
advanced-ratcheting
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