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Feb 03, 2006


Alan Johnston

Hi Irwin,

Thanks for your posting about ZRTP. I wanted to make two clarifications. First, Phil's last name has two n's ;-) Secondly, your posting makes it sound as if ZRTP is in competition with SRTP, when in fact the reverse is true. ZRTP performs key agreement (setup and configuration) for SRTP, so the two protocols must be used together.

SRTP is widely implemented, and is a proven protocol that works. However, the key agreement protocol needed to use SRTP is a source of frustration in the industry - there are multiple incompatible methods using SIP, and there are no methods when different signaling protocols (e.g. SIP and H.323, for example) are utlized in calls through a gateway. The problems I mentioned on the VOIPSA list are not problems with SRTP but with associated key agreement protocols. ZRTP aims to solve this problem by using the lowest common denominator of nearly all VoIP systems - RTP - to setup and configure SRTP sessions. As such, ZRTP should help the deployment of SRTP.

As an update, the ZRTP draft is nearly complete and will be discussed in the AVT Working Group at the next IETF meeting in Dallas, TX the week of March 19.


Irwin Lazar

Alan, thanks for your comments & clarifications. I look forward to reading the draft.

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