Subject: [AVT] RFC 3711 - questions about cryptographic context

From: tal shahar <[email-masked]>
Date: Sun, 9 May 2004 02:03:09 -0700 (PDT)

hi 
in 3.2.1.  Transform-independent parameters
1. the RFC states that the cryptographic context should hold the the master key(s)
assuming I wish to have SRTP and SRTCP sharing the same master key, what is the situation where I have more than one key
2. if I have only one master key, why do I need to hold the MKI
 
thanks a lot
tal

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From: "David A. McGrew" <[email-masked]>
Date: Sun, 9 May 2004 06:13:39 -0700

Tal,

On May 9, 2004, at 2:03 AM, tal shahar wrote:

> assuming I wish to have SRTP and SRTCP sharing the same master key, 
> what is the situation where I have more than one key

if I understand right, you are wondering why the "(s)" appears in the 
quote from the RFC.  This is because there might be multiple master 
keys, each of which is used for a particular range of the packet index 
(that is, the 48-bit integer that is the concatenation of the ROC and 
the sequence number).  libSRTP does not support this facility, and I 
expect that the vast majority of users won't miss it.

> 2. if I have only one master key, why do I need to hold the MKI

You don't, though you might need to store the fact that you are not 
using an MKI.  libSRTP does not support MKIs as of yet.  I don't think 
that it would be hard to add this feature.

David