| 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]
- ^ Cite error: The named reference
advanced-ratchetingwas invoked but never defined (see the help page). - ^ a b c Ermoshina, Ksenia; Musiani, Francesca; Halpin, Harry (September 2016). "Internet Science". In Bagnoli, Franco; et al. (eds.). Internet Science. INSCI 2016. Lecture Notes in Computer Science. Vol. 9934. Florence, Italy: Springer. pp. 244–254. doi:10.1007/978-3-319-45982-0_22. ISBN 978-3-319-45982-0.
- ^ "WhatsApp's Signal Protocol integration is now complete". Signal. Signal Blog. 2016. Archived from the original on 29 January 2021. Retrieved 5 April 2016.
- ^ Cite error: The named reference
:0was invoked but never defined (see the help page). - ^ Unger et al. 2015, p. 241
- ^ Frosch et al. 2016