since some time SC supports the latest version of the ZRTP specification
that is currently nearly an RFC. The process at IETF is ongoing and,
according to the tracker, the last steps are processed.
Having said that I would like to give some warning about the use of ZRTP:
Due to some modifications in the ZRTP specification and hence the
implementation it is not longer possible to start ZRTP on half-duplex
Usually this is not a problem on audio sessions because these are usually
(maybe not always) full-duplex, that is each SC has a send and a receive
audio stream. After the audio stream was switched to secure mode you will
hear a short sound notification, the "security sound".
The behaviour is different for video: each party can switch on video
after some time. Only if _both_ parties enabled video for an overlapping
time thus establishing a full-duplex video stream ZRTP will start to
negotiate the required security data and can start SRTP to encrypt the
stream. If only _one_ party enables video than this half-duplex video
stream is _not_ encrypted. If the video channel is switched to secure
mode both parties again hear the short "security sound" notification and
the tool tip of the connection shows the correct security status.