Subject: [AVT] draft-ietf-avt-srtp-03.txt

From: "David A. Mcgrew" <[email-masked]>
Date: Thu, 14 Mar 2002 10:27:30 -0800

Hello,

I'd like to outline the changes to draft-ietf-avt-srtp-03.txt (from version
02) and touch on the topics for discussion next week.

We added an optional field to both SRTP and SRTCP packets, called a master
key identifier, or MKI.  This field indicates the master key used to protect
the packet, as is useful when frequent re-keying is used.  In scenarios in
which the key is static, the optional field would not be present.  This
addition was motivated by review which found synchronization problems
associated with changing master keys.

The TMMH key size for large packets was reduced, in order to facilitate its
use with large (e.g. not VoIP) packets.  TMMH version two is defined,
following the same academic work as the earlier version.  This change was
motivated by comments on the list and from other reviewers.

We tweaked our AES Counter Mode definition in order to avoid 128 bit modular
arithmetic and to take advantage of SSRC uniqueness in some scenarios.

We added a 'salt' field as an additional input to the key derivation
function, in order to make that function secure even when used with
arbitrary encryption and authentication mechanisms.  This change was
motivated by security review done by the authors.

We added ‘scenarios’ Section to provide guidance on how to use SRTP various
options in different unicast and multicast scenarios.

Martin Euchner pointed out that it might be worthwhile to allow both
orderings of SRTP and FEC.  It may be possible to do this without major
changes to the specification or to implementations.

Feedback on this issue is welcome.  I've copied my coauthors to keep them in
the loop.

See you in MN.

dam

David A. McGrew, Ph.D.
Manager, Strategic Crypto Development
IOS Technologies Division
Cisco Systems, Inc.
(301) 349 5815

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