Subject: [MMUSIC] MKI length and MKI format

From: Vavilapalli Srikanth-A19563 <[email-masked]>
Date: Wed, 26 Jan 2005 00:12:21 +0530

Mark and MMUSIC community

Ref: <draft-ietf-mmusic-sdescriptions-08.txt> Section:5.1 Page:14

It was specified in the draft that the MKI length is the size of the MKI
field in the SRTP packet, specified in Bytes. And the upper limit for that
value is 128 Bytes. Is it (128) Bytes or (128) bits? What is the intention
of keeping such a big value for the MKI length value?

Also what is the data type of MKI? Is it an "integer" of length specified by
MKI-Length or a "byte string" of length specified by MKI-Length?

According to the example "1026:4" given in the draft, it was said that the
example assigns to the key a master key identifier of 1026 that is 4 bytes
long. In this case what is the value of MKI filed in each SRTP packet? Is it
"1026" or "0402" (where 1026 = 0x0402)?

Please clarify me in this regard.

Regards
Srikanth

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From: Mark Baugher <[email-masked]>
Date: Tue, 25 Jan 2005 11:04:36 -0800

hi Srikanth,

On Jan 25, 2005, at 10:42 AM, Vavilapalli Srikanth-A19563 wrote:

> value is 128 Bytes. Is it (128) Bytes or (128) bits?

It's in bytes, that's clear.
> What is the intention

It has a high upper bound in order to help with possible future 
migration of digital TV services to IP networks.  I expect that two or 
four bytes would be the typical value.  We made the upper bound 
configurable in the SRTP specification owing to the practice found in 
TV conditional access systems that use a key indicator to encode a 
variety of information for a broadcast receiver.  I was told by people 
from NDS and Nagra that they would prefer the size to be configurable.  
We did not see any reason why it should not be, but we have not yet 
seen any applications materialize for this particular feature.  I'd be 
interested to know what the Motorola Digicipher folks think - when they 
think about video over IP.

I cannot imagine that the MKI will serve any telephony purpose 
whatsoever.  The default size is zero and this is what is mandatory to 
implement (and test).

> MKI-Length or a "byte string" of length specified by MKI-Length?

It is a byte string.
> "1026" or "0402" (where 1026 = 0x0402)?

Sorry, we're using decimal and not hexadecimal.  That should have been 
pointed out in the document.

Mark