General

This GStreamer plugin zrtpfilter supports the ZRTP protocol as defined in RFC 6189. The plugin also contains a SRTP/SRTCP implementation that support different key lengths.

The current layout of zrtpfilter:

         +-------------------------------------+
         |              zrtpfilter             |
         +---------------+      +--------------+
         |recv_rtp_sink  |      |recv_rtp_src  |
from     |               |      |              |  to RTP
network  +---------------+      +--------------+  plugin,
plugin,  |                                     |  e.g.
e.g.     +---------------+      +--------------+  rtpbin
udpsrc   |recv_rtcp_sink |      |recv_rtcp_src |
         |               |      |              |
         +---------------+      +--------------+
         |                                     |
         +---------------+      +--------------+
         |send_rtp_sink  |      |send_rtp_src  |
         |               |      |              |  to
from RTP +---------------+      +--------------+  network
plugin,  |                                     |  plugin,
e.g.     +---------------+      +--------------+  e.g.
rtpbin   |send_rtcp_sink |      |send_rtcp_src |  udpsink
         |               |      |              |
         +---------------+      +--------------+
         |                                     |
         +-------------------------------------+

The plugin is a full-duplex plugin that handles up- and downstream traffic for RTP and RTCP. If connected with another ZRTP enabled client it automatically negotiates the SRTP keys and enables SRTP and SRTCP. This is fully transparent to the connected up- or downstream plugins.

Building

NOTE: This is a beta version for for testing and start production coding!

The only prerequisits the build GStreamer ZRTP are:

• openSSL development environment (optional, see CRYPTO_STANDALONE variable in CMakeLists.txt)
• a C and C++ compiler (tested with gcc and g++)
• installed GStreamer base including development environment. Make sure you have also gstreamer-rtp package installed.
• This plugin uses cmake to generate the build files.

The use git clone to get the sources from github and change into the gstZrtp directory. Before starting to build you need to get the ZRTP and SRTP sources:

sh getzrtp.sh

This script clones the current ZRTP/SRTP source repository (also on github) into the zrtp subdirectory. If this subdirectory already exists it checks if it contains a Git repository and updates the sources with git pull. The build process uses these sources and puts the compiled objects into the zrtpfilter shared library. This avoids a dependcy to the standard ZRTP library and is more inline with GStreamer's binary-only plugin concept.

Now create a build directoy and create the build scripts:

mkdir build
cd build
cmake ..

Just call make as usual to build the shared library for the plugin. cmake places this library in the build/src subdirectory und us can use it, for example with gst-launch:

gst-launch --gst-plugin-path=/your/path/gstZrtp/build/src ...

Some documentation

The zrtpfilter plugin contains gtkdoc compliant documentation. To create the documentation change to the doc directory and run the shell script generateDoc.sh. The cmake call (see above) generates this script and you can use it after you built the plugin. As usualy gtkdoc places the documentation in the html subdrirectory. Use your browser and open the index.html file.

Demo programs and sources

The demo directory contains some programs that show how to use zrtpfilter in various configurations.