Re: [6tisch] 6tisch join requirements for 6top

Thomas Watteyne <watteyne@eecs.berkeley.edu> Tue, 02 December 2014 06:58 UTC

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References: <D0876D12.C03C%rsudhaak@cisco.com> <32412.1415737868@sandelman.ca> <D087B62D.C081%rsudhaak@cisco.com> <10653.1415740821@sandelman.ca> <CADJ9OA_LFkGDuyG_0bf=07d7cvC9FNRr5cMGTmYw2PR=g9XQHA@mail.gmail.com> <8193.1416253349@sandelman.ca> <21619.12717.53454.214321@fireball.kivinen.iki.fi> <E045AECD98228444A58C61C200AE1BD848A77CB5@xmb-rcd-x01.cisco.com> <21620.25926.119766.130028@fireball.kivinen.iki.fi> <54750807.9070901@berkeley.edu> <CADJ9OA_FS2qsTEGCDMMu_wwN=NsfARW26rw_9g9ROP=AHorB3g@mail.gmail.com> <674F70E5F2BE564CB06B6901FD3DD78B29D05F10@TGXML210.toshiba.local> <7934.1417488456@sandelman.ca>
From: Thomas Watteyne <watteyne@eecs.berkeley.edu>
Date: Mon, 01 Dec 2014 22:58:30 -0800
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To: Michael Richardson <mcr+ietf@sandelman.ca>
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Cc: Kris Pister <ksjp@berkeley.edu>, "6tisch@ietf.org" <6tisch@ietf.org>, "yoshihiro.ohba@toshiba.co.jp" <yoshihiro.ohba@toshiba.co.jp>
Subject: Re: [6tisch] 6tisch join requirements for 6top
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Yoshi,

There is some weakness if a device does not store a frame counter (i.e.,
> ASN in TSCH) across a reboot.  There can be a replay attack by sending a
> copy of beacon fame sent in the past, letting the rebooted device to re-use
> the frame counter (until the device synch up with correct ASN).


A mote reboot will rejoin the network. The network will have advanced in
time (i.e. the value of the ASN will have increased). When the node
re-joins the network, it will hear the (updated) ASN and start using that.
So a node doesn't need to store the ASN in non-volatile memory, since it
will not reuse the same value after a reboot.

Thomas

On Mon, Dec 1, 2014 at 6:47 PM, Michael Richardson <mcr+ietf@sandelman.ca>
wrote:

>
> <yoshihiro.ohba@toshiba.co.jp> wrote:
>     > There is some weakness if a device does not store a frame counter
>     > (i.e., ASN in TSCH) across a reboot.  There can be a replay attack by
>     > sending a copy of beacon fame sent in the past, letting the rebooted
>     > device to re-use the frame counter (until the device synch up with
>     > correct ASN).
>
> First, let's assume that the node has been removed from the network, and is
> subject to a malicious beacon frame.  It can never catch up, I guess.  If
> the
> attacker had a record of subsequent (encrypted) frames that were present,
> the
> captured node would decrypt the traffic again.
>
> At this point, if one controls the node sufficiently that one can read ram,
> one could read the cleartext; but I would claim that in that case, one
> already has the key, and just decrypt the captured traffic directly.
>
> If we are talking about join traffic, it seems that already have the
> encryption key, so one doesn't even need the node, or the beacon frame.
>
> Is there another attack?
>
> Now, assuming that we have both malicious and regular transmitters of the
> beacon.  Is there something else one can do?
>
> --
> ]               Never tell me the odds!                 | ipv6 mesh
> networks [
> ]   Michael Richardson, Sandelman Software Works        | network
> architect  [
> ]     mcr@sandelman.ca  http://www.sandelman.ca/        |   ruby on
> rails    [
>
>
>