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ZRTP encryption


   ZRTP is a key agreement protocol to negotiate the keys for encryption
   of RTP in phone calls. It is a proposed public standard: [8]ZRTP: Media
   Path Key Agreement for Secure RTP.

   Even though it uses public key encryption, a PKI is not needed. Since
   the keys are negotiated in the media path, support for it in signaling
   is not necessary. ZRTP also offers opportunistic encryption, which
   means that calls between UAs that support it are encrypted, but calls
   to UAs not supporting it are still possible, but unencrypted. The
   actual RTP encryption is done with [9]SRTP. For more information about
   ZRTP, see the [10]Zfone project, the [11]draft and the [12]wikipedia


   Since the version 1.0 SEMS supports ZRTP with the use of the [13]Zfone

   To build SEMS with ZRTP support, install the SDK and set WITH_ZRTP=yes
   in Makefile.defs, or build with
 $ make WITH_ZRTP=yes

   The conference application is enabled to tell the caller the SAS phrase
   if it is compiled with WITH_SAS_TTS option, set in
   apps/conference/Makefile. For this to work, the [14]flite
   text-to-speech synthesizer version 1.2 or 1.3 is needed.

Online demo



   for a test drive of ZRTP conferencing. If you call that number with a
   ZRTP enabled phone, you should be told the SAS string that is also
   displayed in your phone. Press two times the hash (##) while in the
   call to read out the SAS string again.

How to use ZRTP in your application

   Have a look at the conference application on how to add ZRTP support in
   your application. There is a void AmSession::onZRTPEvent(zrtp_event_t
   event, zrtp_stream_ctx_t *stream_ctx) event that is called with the
   appropriate ZRTP event type and the zrtp stream context, if the state
   of the ZRTP encryption changes. The zrtp_event are defined in the Zfone


   The Zfone SDK is licensed under the Affero GPL v3. As SEMS is licensed
   under GPL 2+, you may use SEMS under GPLv3 and link with libZRTP under
   Affero GPL v3. You may use the resulting program under the restrictions
   of both GPLv3 and AGPLv3.

   Note that due to the nature of the GPL, without written consent of the
   authors of SEMS as with any other non-free library, it is not possible
   to distribute SEMS linked to specially licensed commercial version of
   the libZRTP SDK, nor the AGPL version. If in doubt, talk to your

Phones with ZRTP

     * [17]Zfone turns every softphone into a secure phone by tapping into
       the RTP sent and received
     * [18]Twinkle is a very good free softphone for Linux. It can speak
       ZRTP with the use of GNU [19]libzrtpcpp.

    Generated on Thu Feb 3 02:29:25 2011 for SEMS by  [20]doxygen 1.6.1


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   8. http://tools.ietf.org/html/draft-zimmermann-avt-zrtp
   9. http://www.ietf.org/rfc/rfc3711.txt
  10. http://zfoneproject.com/
  11. http://tools.ietf.org/html/draft-zimmermann-avt-zrtp
  12. http://en.wikipedia.org/wiki/ZRTP
  13. http://zfoneproject.com/prod_sdk.html
  14. http://cmuflite.org/
  15. mailto:secureconference@iptel.org
  16. mailto:zrtp@iptel.org
  17. http://zfoneproject.com/
  18. http://twinklephone.com/
  19. http://www.gnutelephony.org/index.php/GNU_ZRTP
  20. http://www.doxygen.org/index.html