Subject: [MMUSIC] SDP Support for exchanging different auth tag length for SRTP and SRTCP

From: Vavilapalli Srikanth-A19563 <[email-masked]>
Date: Wed, 22 Dec 2004 14:21:02 +0530

Hi

Ref: <draft-ietf-mmusic-sdescriptions-07.txt>

In this draft, I did not find a way to exchange the both SRTP and SRTCP
authentication tag lengths using SDP secure attributes. 

i.e. if a SRTP application wishes to use 32-bit weak authentication for SRTP
packets and 80-bit strong authentication for SRTCP packets and has chosen
the mechanism described in the above draft to communicate between sender and
receiver, How can a offerer/answerer include this information in the
a=crypto line of SDP offer or answer respectively?

Regards
Srikanth

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From: Mark Baugher <[email-masked]>
Date: Wed, 22 Dec 2004 06:22:18 -0800

hi Srikanth,

> authentication tag lengths using SDP secure attributes.

There is no way to specify a different cryptographic policy for SRTP 
and SRTCP in sdescriptions.  The reason for that is that I think it's a 
bad idea to have unnecessary complexity in a security protocol.
> a=crypto line of SDP offer or answer respectively?

They can't.  If someone wants to introduce this level of complexity 
into SRTP signaling, then they can write their own sdescriptions draft. 
  sdescriptions is extensible, but I think it's better to keep things as 
simple as they can be.  Allowing multiple policies within an SRTP 
session to me isn't simple.  SRTP as a protocol does admit separate 
policies for SRTP and SRTCP.  sdescriptions supports only a single 
policy per session.

Cheers, Mark

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From: Mark Baugher <[email-masked]>
Date: Mon, 27 Dec 2004 09:19:32 -0800

This question has been answered, has it not?

Mark