Re: [Gen-art] [6tisch] Review of draft-ietf-6tisch-minimal-17

Tero Kivinen <kivinen@iki.fi> Thu, 05 January 2017 16:04 UTC

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Date: Thu, 5 Jan 2017 18:04:45 +0200
From: Tero Kivinen <kivinen@iki.fi>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Cc: gen-art@ietf.org, "6tisch@ietf.org" <6tisch@ietf.org>, Thomas Watteyne <thomas.watteyne@inria.fr>, draft-ietf-6tisch-minimal.all@ietf.org
Subject: Re: [Gen-art] [6tisch] Review of draft-ietf-6tisch-minimal-17
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Brian E Carpenter writes:
> Hi Thomas,
> 
> The responses to my comments almost all look fine to me. Just one point,
> on MINOR COMMENT 4 (slide 8):
> 
> "Shouldn't this also say that this value MUST NOT be used in
> operational networks?" 
> 
> We've seen many cases over the years of informal values making it into shipped
> products... generally a Bad Thing. But with my lack of IEEE802.15.4 expertise,
> I really don't know whether it matters in this case. Whatever the WG decides
> is good, as long as the point is considered.

It does matter. If anybody knows the key they can do single packet DoS
attack against network and kill it...

I.e. send EB to some of the nodes, so that it changes the schedule.
After that the nodes in the network are out of sync, and after few
minutes or tens of minutes they will realize this and start to
recover, but it takes long time, and can cause lots of disruption.

If node receives EB which says that the EB slot is not timeslot 0, or
that it has channel offset of 1 or something like that, then it will
be listening EBs from wrong channel after that. After it misses enough
of packets from the network it realizes it is out of sync and
reinitializes itself back to network. This means it needs to do
passive scan over the 16 channels listening each channel for slot
frame size * timeslot duration * EB_PERIOD (at minimum, perhaps twice
in case it happens to miss EB). Meaning that with 101 slot frames, and
10ms timeslot duration, and with EB_PERIOD of 3 that is 3 seconds per
channel, and for 16 channels it takes 48 seconds.

During that time nodes which were children of that node, will notice
that it has gone, and they will start doing same...

The attacker can cause even more confusion by changing the timeslot
parameters, or channel hopping order, but I would hope that
implementations would ignore changes to those IEs while the network is
running.

On the other changing channel offset or timeslot number for EBs, is
something that might happen, so nodes might need to cope with that.

I have complained this clear text password in the specification for
long time, and I do not think there is any reason to include that key
in the RFC. The early interoperability testing people can agree on key
they use in the interoperability events it does not need to be
hardcoded in the RFC or in the code.

> I hope the interim goes well, it is too far out of my time zone to attend!
-- 
kivinen@iki.fi