Date: Thu, 28 May 2009 00:55:27 +0200
   From: Zach Shelby <[email protected]>

   A new version of draft-ietf-6lowpan-nd is now available at:

   http://www.ietf.org/internet-drafts/draft-ietf-6lowpan-nd-03.txt

Zach,

The security section says that MAC sublayer cryptography
is expected to provide:

   secure unicast to/from Routers and secure broadcast from
   the Routers in a way that prevents tampering with or
   replaying the RA messages.

802.15.4 security does not provide replay protection.  It
does have a means for including frame counters in messages,
but there is no mechanism for synchronizing frame counters
in the first place.  The frame counters prevent messages
from being replayed out of order, but they do not prevent
replaying in general.  This seems particularly important for
RA messages, which are often some of the first packets
traveling over a link or the first packets received after a
reboot.

It may be that the limited replay protection that 802.15.4
security provides is sufficient in this case, but I think
that this needs to be spelled out in more detail.  Either
that or real replay protection needs to be provided by
extending 802.15.4 security or adding additional security
at the 6LoWPAN adaption layer.
                                   -Richard Kelsey
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