Glossary

Shared vocabulary for the WhatsApp calls protocol. Generated from spec/glossary.yaml.

Term	Definition
call-creator	The JID of the device that created/initiated the call. Together with call-id it uniquely identifies a call, disambiguating cases where the same call-id space might otherwise collide across the two endpoints.
call-id	An identifier uniquely naming a single call instance. Combined with call-creator it keys the call across both peers and the server, and ties together the offer, accept/reject, transport updates, and terminate for that call.
Double Ratchet	The Signal Protocol's ratcheting algorithm that derives a fresh message key for every message, combining a Diffie-Hellman ratchet with symmetric key chains to provide forward secrecy and break-in recovery. Established messages (type msg) use it.
ICE	Interactive Connectivity Establishment, the NAT-traversal framework for negotiating a working media path between peers by gathering and testing candidate transport addresses. WhatsApp's / relay candidates are an ICE-like mechanism.
JID	Jabber/XMPP Identifier addressing a WhatsApp account or device, e.g. user@s.whatsapp.net, with a device suffix (user.deviceId@...) under multi-device. Call stanzas use JIDs in from/to and in call-creator to route between specific devices.
msg	A normal SignalMessage: the type used to deliver the call/media key over an already-established Double Ratchet session, the common case between contacts that have interacted before.
multi-device	WhatsApp's architecture allowing several linked devices (phone plus companions) to share one account, each with its own Signal identity. For calls it means an offer may carry one per peer device, and "elsewhere" terminate reasons stop other devices ringing once one answers or declines.
Noise Protocol	The Noise Protocol Framework handshake (WhatsApp uses an XX-style pattern) that establishes the encrypted transport for the multi-device WebSocket connection. All WABinary traffic, including call signaling, rides inside this Noise-encrypted channel; it secures the client-to-server link and is distinct from the end-to-end Signal layer.
pkmsg	A PreKeySignalMessage: the type used when no Signal session exists with the target device yet, carrying X3DH handshake material to establish the session before decrypting the wrapped call/media key.
prekey	A pre-generated public key (signed prekey and one-time prekeys) published to the server so others can run X3DH and start a Signal session asynchronously. Consuming a one-time prekey is what enables a pkmsg-type to establish a fresh session for call key delivery.
Signal Protocol	The end-to-end encryption protocol (X3DH key agreement plus the Double Ratchet) used between user devices. In calls it protects the payload that delivers the call/media key, so even WhatsApp servers relaying the stanza cannot read the key.
SRTP	Secure Real-time Transport Protocol, the encrypted media transport for call audio/video, carried as UDP packets to WhatsApp voip relay servers. SRTP session keys are derived from the call/media key delivered over the Signal-encrypted nodes in signaling.
TURN/relay	TURN (Traversal Using Relays around NAT) servers relay media when a direct peer path is not possible. WhatsApp routes call media through its own voip relay servers; the transport endpoints (/) advertised in signaling identify these relays.
WABinary	WhatsApp's compact binary encoding of an XMPP-like stanza tree (tag, attributes, children) used on the wire instead of textual XML. Call signaling stanzas such as are WABinary nodes. Tokenised dictionaries and binary value types make it smaller than XML while preserving the same logical structure.
X3DH	Extended Triple Diffie-Hellman, the asynchronous key-agreement step of the Signal Protocol. It lets one device establish a shared secret with another using published prekeys without both being online, bootstrapping the session that later messages (type pkmsg) ride on.

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