Call encryption (SRTP and TLS)
Call encryption protects VoIP calls from interception by encrypting both the signalling that sets up the call, usually with TLS, and the audio itself, usually with SRTP.
How call encryption works
A VoIP call has two parts, and each is protected separately:
- Signalling — the messages that set up and end the call, including who is calling whom. TLS encrypts this, the same technology that secures websites. WSS (secure WebSocket) is a similar option used by browser-based phones.
- Media — the audio. SRTP (secure real-time transport protocol) encrypts it. The encryption keys are agreed in one of several ways: SDES (through the encrypted signalling), DTLS (a separate key exchange) or ZRTP (directly between the two devices).
Without encryption, someone with access to the network could, in principle, listen to calls.
Call encryption in phone.systems™
The phone.systems™ app encrypts SIP signalling and media with TLS and SRTP. For IP phones and third-party softphones, SIP accounts support TLS and WSS transports and SRTP with SDES, DTLS or ZRTP; you choose the settings that your device supports. Calls that leave phone.systems™ for the regular phone network follow the security of that network. See the business phone app.