WhatsApp uses SRTP, the Secure Real-time Transport Protocol, for encrypted calls.
SRTP is an extension of the Real-time Transport Protocol, or RTP, which carries time-sensitive media such as voice and video. It adds protections including encryption, message authentication, and replay protection, helping prevent attackers from reading or tampering with call media in transit.
WhatsApp’s call security involves more than SRTP alone. The application also uses signaling and key-management mechanisms to establish calls, while WhatsApp’s broader messaging system uses the Signal Protocol for end-to-end encrypted chats. SRTP specifically describes the secure transport of real-time call media.
The distractors belong to different networking roles. IMAP retrieves email, SFTP transfers files over SSH, and HTTPS secures web traffic. They can all be important internet protocols, but none is the canonical protocol named for WhatsApp’s encrypted voice and video call media.