Subject: [AVT] SRTP_PREFIX_LENGTH

From: Vavilapalli Srikanth-A19563 <[email-masked]>
Date: Mon, 22 Nov 2004 18:31:19 +0530

Hi

Another question from my side:

RFC 3711: Section 4.1: Page 19: SRTP_PREFIX_LENGTH is the octet length of
the key-stream prefix, a non-negative integer, specified by the message
authentication code in use.

RFC 3711: Section 4.1: Page 20: SRTP_PREFIX_LENGTH, the key-stream prefix is
indicated by a positive, non-zero value of SRTP_PREFIX_LENGTH.

It looks like the second bullet is restricting zero value for
SRTP_PREFIX_LENGTH. In that case, how can HMAC-SHA1 use a zero length
key-stream prefix?

	RFC 3711: Section 4.2.1: Page 25: With HMAC-SHA1, the
SRTP_PREFIX_LENGTH SHALL be 0.

Am missing something here? Please clarify this point.

Thanks & Regards
Srikanth Vavilapalli

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of David
A. McGrew
Sent: Friday, November 19, 2004 9:25 PM
To: milo diurn
Cc: [email-masked]; [email-masked];
[email-masked]; [email-masked]
Subject: Re: [AVT] RFC3711: Srtp Parameters for Rx/Tx ?

Hi Milo,

On Nov 19, 2004, at 7:10 AM, milo diurn wrote:

> Karl, and Srtp community,
>
> In RFC3711, I do not see any clear way of setting the Srtp parameters 
> (chap 8.2)
> for both ways of the session:
> - Transmit : need the Srtp parameters for Encryption (to be sent to 
> the network)
> - Receive: need the Srtp parameters for Decryption (to be received 
> from the network).

essentially, the parameters are established out-of-band for SRTP.  The 
transmit/receive issue doesn't affect this point; either SRTP endpoint, 
or a third-party device (e.g. a call controller) could set the 
parameters.  In this respect, SRTP is like RTP: it relies on another 
protocol to signal the context information needed to get it going.  
MIKEY and the SDP Security Descriptions are two standards-track ways of 
signaling SRTP.

David

>
> Could you, please, clarify this point ?
>
> Thanks
>
> Regards
>
> _________________________________________________________________
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_______________________________________________
Audio/Video Transport Working Group
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_______________________________________________
Audio/Video Transport Working Group
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https://www1.ietf.org/mailman/listinfo/avt