RE: [AVT] draft-zimmermann-avt-zrtp-00.txt

["Even, Roni" <roni.even at polycom.co.il>]

Hi,
I read the draft and find it interesting I have some questions.

1. The key exchange is done after the RTP connection is established,
this means that until the end of key exchange both sides will send
non-encrypted information. I think that the document should address the
issue. One way is to recommend using no-op packets until the system will
start to encrypt and indicating this to the user.

2. It is not clear to me how does the receiver know which is the first
packet that is encrypted.

3. In section 10 you have "If both UAs support ZRTP, they will first try
ZRTP before attempting SRTP". I assume that it means that even though
the sides already have a shared secret they should not start SRTP and do
ZRTP exchange first. What is the reason for that. Based on my first
comment it will make sense to start SRTP when starting to send media and
maybe use re-key based on ZRTP.

4. In section 3.1 "If none of these are supported, an RTP packet
containing
   comfort noise can be generated to carry a ZRTP message." I understand
that ZRTP is not only for audio so comfort noise is not a video or
application payload. The common mode is no-op which was defined to all
media types.

Thank
Roni Even 

-----Original Message-----
From: Alan Johnston [mailto:alan at sipstation.com] 
Sent: Monday, February 27, 2006 3:57 PM
To: avt at ietf.org
Cc: Philip Zimmermann
Subject: [AVT] draft-zimmermann-avt-zrtp-00.txt

All,

We have just submitted a new Internet-Draft 
draft-zimmermann-avt-zrtp-00.txt.  Until it becomes available in the 
archives, you can get a copy at:

   http://www.philzimmermann.com/zfone/draft-zimmermann-avt-zrtp-00.txt
   http://www.philzimmermann.com/zfone/draft-zimmermann-avt-zrtp-00.html

We will request a slot in AVT in Dallas to discuss.  Discussion about 
the RTP extensions and mechanism are best held on the AVT list while 
discussions about key management for SRTP are best held on the MMUSIC 
list, with some cross posting as needed.

Thanks,
Alan

- - -

ZRTP: Extensions to RTP for Diffie-Hellman Key Agreement for SRTP
                   draft-zimmermann-avt-zrtp-00

Abstract

This document defines ZRTP, RTP (Real-time Transport Protocol) header
extensions for a Diffie-Hellman exchange to agree on a session key
and parameters for establishing Secure RTP (SRTP) sessions.  The ZRTP
protocol is completely self-contained in RTP and does not require
support in the signaling protocol or assume a Public Key
Infrastructure (PKI) infrastructure.  For the media session, ZRTP
provides confidentiality and, in cases where a secret is available
from the signaling protocol, authentication.


_______________________________________________
Audio/Video Transport Working Group
avt at ietf.org
https://www1.ietf.org/mailman/listinfo/avt

_______________________________________________
Audio/Video Transport Working Group
avt at ietf.org
https://www1.ietf.org/mailman/listinfo/avt