David, Just checkin in on you... my cell is 918-424-9378 /b On Jul 21, 2008, at 8:33 AM, David Sugar wrote:
In an IP-PBX that must operate as a b2bua (back-to-back user agent), there are two possible arrangements for implimenting ZRTP. The first is through PBX enrollment, which makes the IP-PBX a fully trusted (and hence insecure) man-in-the-middle. The second method requires PBX transparency, where the channel between ua's is not decrypted at the server, and where this will still work when the call is routed to an insecure destination (telephony card, non-zrtp extension, etc) where decryption must occur. This latter method requires a lot more work to get correct....
In the GNU project, we have a zrtp stack as an extension to ccrtp (the GNU RTP Stack) as noted here, libzrtpcpp. There is an asterisk module for zrtp available from Phil Zimmerman's site. We also have been working on a Java based stack which is in svn but not "released" yet, and that works with SIP communicator. Our own chosen solution was not to use or extend an existing b2bua based IP-PBX architecture (like say for example Bayonne), but rather to design a new call SIP call server explicitly for handling secure calling, which is GNU SIP Witch.
Robert Clayton wrote:
Is anyone attempting to implement the ZRTP cryptographic key- agreement protocol (a method of encrypting voice data using self-generated keys, rather than keys from certificate authorities). Some softphones such as X-Lite already implement it. There is apparently an open source library at ftp://ftp.gnu.org/gnu/ccrtp/libzrtpcpp-0.9.0.tar.gz
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