[VOIPSEC] ZRTP and Asterisk

[Alejandro Cabrera Obed]

Dear all, I have Asterisk 1.4.13 as a SIP server routing all the RTP
calls through it (there ara not any RTP traffic client-to-client) with
two types af clients: Twinkle+libzrtp and SJPhone+Zfone, both managing
ZRTP as the encryption method for SIP/RTP conversations.

I read from Phill Zimmerman that ZRTP only works if I apply a patch to
my Asterisk, but now I haven't any patch in my Asterisk and ZRTP works
among Twinkle clients but doesn't work among SJPhone-to-SJPhone nor
Twinkle-to-SJPhone clients.

Why can I use ZRTP in Asterisk just among Twinkle clients ??? After
click on the SAS (short authentication string) I see the lockpad in the
clients and I can  encrypt the calls.

Do you know the way to successfully implement ZRTP on Asterisk nowadays ???

Thanks a lot

Alejandro