Signaling over TLS and encrypted audio, for desk phones and for providers.
Phones can now connect over an encrypted connection, and the audio itself can be encrypted too.
Two things to protect
A phone call has two parts, and they are protected separately.
- Signaling: who is calling whom, and the passwords that prove it. This now travels over TLS, the same protection a bank's website uses.
- Audio: the conversation. This is encrypted with SRTP, so a recording of the network traffic is noise.
Each side on its own terms
Because every call is two legs with the system in the middle, each leg is settled separately. An encrypted phone and an older plain one can still talk to each other. So can an encrypted phone and a provider that offers no encryption.
A phone gets encrypted audio when it connected over TLS. A provider gets it when its settings say so.
Certificates
Encryption needs a certificate. The system makes its own the first time it starts and keeps it, so phones do not see a new one after every restart. An office with a proper certificate can use that instead.
Set up for you
Phones set up by link are told to use the encrypted connection, with encrypted audio required, on models that support it. Nobody has to find the right screens on the phone.
A switch for later
There is a setting to refuse any phone that is not encrypted. It is off by default, because switching it on would cut off phones set up before this existed. Turn it on once every phone has been moved over.
What it does not cover
Encryption protects the call between the phone and the system. What happens beyond a provider, on the public telephone network, is outside anyone's control.