Simple definition
Secure Real-time Transport Protocol encrypts and authenticates RTP voice or video packets.
Purpose and use
SRTP, Secure Real-time Transport Protocol, protects RTP with confidentiality, integrity and replay-defense mechanisms according to the selected profile.
How does it work?
Participants use shared keys and parameters established through an associated mechanism. SRTCP protects RTCP control exchanges.
Example and verification
During a VoIP security review, verify the actually negotiated profile and protection on each segment, including intermediary devices.
Points to watch
SIP over TLS does not prove that media uses SRTP. A media-terminating SBC can create separate protected legs rather than end-to-end encryption.
In short
Assess signaling, key management and media transport separately when evaluating call protection.