It is very easy to use Linphone to place secure calls, using ZRTP encryption protocol and TLS transport.
Follow these steps:
Choose a SIP provider that supports authenticating and transporting traffic through
TLS (not all do), like Linphone SIP service or Ostel.
Install Linphone 3.7.0, mainly because this version allows to "configure multiple proxy accounts with different transports (UDP, TCP, TLS)". But this of course is not a requirement, more like cosmetics, and older versions would do just fine.
Add a SIP account in Linphone (using the above-mentioned providers) and for each account, in the
SIP Account Configuration dialogue set
TLS (instead of
Options > Prefs > Network Settings set
Media encryption type to
You can check that all works as expected by calling the Ostel Echo testing service
sip:email@example.com and verifying that you see the message:
Secured by ZRTP - [auth token: ab34]
As for the required criteria, Linphone:
- supports placing audio/video calls,
- allows encrypting the media stream using open standards,
- runs on most modern Linux distributions (Fedora, Debian, Ubuntu, Gentoo, etc.),
- apparently has some OpenBSD ports (but I have little experience with those),
- is fully open-source, although the company behind it also provides commercial support
Also, Linphone has impressive cross-platform support:
Linphone has been launched in 2001. It was the very first open source application using SIP software on Linux. For more than 10 years, a lot of improvements have been done and Linphone has been ported on the main desktop, mobile and web platforms:
on Windows Desktop in 2006
on iOS and Android in 2010
on Blackberry OS5-7 in 2011
on Windows Phone 8 in 2013
on web browsers in 2013 (Chrome, Mozilla Firefox, Microsoft Internet Explorer, Apple Safari)
And lastly some personal impressions. I played around with many SIP Softphones (including Ekiga, Jitsi and others who simply crash and burn) and by far Linphone was the most reliable, especially in terms of audio and video throughput. It may be a little choppy wrt to the UI (where Jitsi is superior), even though recently they've made progress on that, but this is just a small nitpick compared to Linphone's technical reliability. It is available on most platforms you could think of, and it is subject to active development, namely wrt codec support (it supports VP8 and H264 video codecs, and Opus and Speex for audio, among others).
As for Skype being secure, I take issue with that. There is anecdotal evidence that Skype calls can be intercepted by the authorities, which implies that Skype keeps backdoors into its encryption mechanisms. I suspect that the NSA would have a harder time intercepting a ZRTP-encrypted Linphone call..