Protection of VoIP Gespchen with SRTP, and/or. additionally with ZRTP

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Hello,

I scanned the Threads of the last 2 years about SRTP, wanted however no old “to hijacken” and therefore a new to the topic opened.

It interests me whether I understood the function mode about SIPS, SRTP and ZRTP.

- SIPS is SIP over TLS, ONLY signaling/connecting negotiating is coded, no protection of the language data.

- SRTP: the audio data (normally over RTP) are coded transmitted, existing problem: Master key exchange still unencrypted, one in the Middle/Impersonation attacks further possible.

- ZRTP: compellingly if SRTP presupposes, however the possibility offers the key to surely exchange, *FALLS* the finger print of the key with the interlocutor is examined over a publication IC key procedure (Diffie Hellmann) (Zfone).

If the receiving station ZRTP supported (however SRTP), no DH-SChlsselaustausch, “do not dropbake” on SRTP, audio data become coded.

The following things interest me now:

1) internal discussions within the same VoIP providers, with me sipgate.de:
I use the Softphones NinjaLite and X-Lite; X-Lite and sipgate.de should actually support SRTP, however I do not have a receiving station with which I that at present test could, can that someone up-to-date confirm?

Sipgate Crypto offers coding of VoIP telephone calls

2) external discussions without SIP more provider, direct via IP or DynDNS/ENUM:
should be protected as far as I know then and state security service 2,0 can not monitor. For which I need then still the Provider Unrersttzung, e.g. Sipgate Crypto with direct IP-Telefonie? For discussions between Softphones with Z/SRTP support actually no more, or?

3) Discussion negotiating over VoIP Provider to other VoIP Provider of the interlocutor
both Provider and naturally the terminals must support SRTP?? here I am not completely safe me…

4) external discussions in the fixed net
would have to be unencrypted actually at the latest at the transition point to the POTS (Plain old of telephones system)

Did I understand so correctly?