Maybe you could describe to us how it should work for a simple protocol
running in a simple network with a single pre-shared key.
I believe that you will be able to do this without a 9 byte security header.
I believe that you will be able to do this in a fully 802.15.4-compliant
way.
ksjp
On 5/22/2015 11:11 AM, Rene Struik wrote:
Hi Kris:
The incoming frame security processing procedure in 802.15.4-2011 (or
in 802.15.4e-2012) does not have as input parameters any state along
the lines of "JOIN-0", etc. Moreover, the procedure for looking up
keys in 802.15.4 does not allow to do whatever one wishes to do: the
word "implicit" only refers to having no explicitly coded key source
field in the auxiliary security header.
Hence, my earlier question to you to describe in detail how one should
instantiate the 802.15.4 spec to arrive at the behavior you suggested.
What you describe below seems something that may look somewhat like
802.15.4 ("is based on"), but certainly does *not* comply with the
specification (to my knowledge this holds no matter whether one
compares to 802.15.4-2003, 802.15.4-2006, 802.15.4-2011, or
802.15.4e-2012).
Best regards, Rene
On 5/22/2015 1:36 PM, Kris Pister wrote:
> I do not understand this, so if you could describe how one can
instantiate a default
> key "6tisch-minimal15" via another mechanism in 802.15.4, that
would be great.
I believe that setting the Key Identified Mode field = 00 implies that
Key is determined implicitly from the
originator and recipient(s) of the frame,
as indicated in the frame header.
Implementers write state machines. When mote is in state "JOIN-0",
load hardware
register RX-MIC-KEY with value K1, set RX-Channel= ...., etc.
ksjp
On 5/22/2015 9:45 AM, Rene Struik wrote:
Hi Kris:
I just wanted to focus on one remark in your email: "You don't need
a 9B header to define this - it's just what the software does to be
compliant with a higher-layer standard."
I do not understand this, so if you could describe how one can
instantiate a default key "6tisch-minimal15" via another mechanism
in 802.15.4, that would be great.
[BTW (I can't resist) - I am not a native speaker, but if one
labels/colors all "6tisch-minimal15" with one brush, this sounds
"crude" to me....]
Rene
On 5/22/2015 12:08 PM, Kris Pister wrote:
[ So far we have fake keys and crude segmentation. I'm going to
have to start naming
any ideas that I may have to contribute. I have some thoughts on
naive networking,
pathetic PKI, and ridiculous routing... :) ]
Key K1 can be whatever you want.
0) If you're doing an interop event, maybe set it to something well
known.
1) If you have a small company and you aren't worried about people
finding
it and publishing it on the internet, set it to some global secret
value [I
don't see how this would work in practice, but maybe...]
2) If you have an out-of-band configuration step, then set it to
the particular
high-entropy cryptographic value for the network that you want the mote
to join.
3) if you have a two-phase join process (Michael - are you calling
this imprint
followed by join? I wasn't sure), then you might have one fake key
for crude
segmentation initially, and then once the production network
credentials are
installed you'd have a pristine key for holy segmentation and
joining for the
production network.
One feature of this approach is that the mechanism is exactly the
same for each choice above. The software and state machine is the
same,
it's the policy that changes according to what the higher-layer
standard
chooses to do.
Whatever value you choose for K1, you will need to store it. The
abstraction
of a macKeyTable gets implemented in software and hardware in a lot
of different
ways. The details are not standardized. Whatever the
implementation interface
is for a given chip and stack, that's the one you use for storing
K1, whatever it's value.
The software can also be written (and is written for many shipping
products)
so that when a mote is trying to synchronize it uses K1 to process
EBs. You don't
need a 9B header to define this - it's just what the software does
to be compliant
with a higher-layer standard.
ksjp
On 5/21/2015 7:29 PM, Rene Struik wrote:
Hi Pascal:
I once again completely lost track of the utterly confusing email
chain regarding the security section of the minimal draft.
With the risk of sounding like a stuck record: this topic had been
documented quite extensively in
draft-struik-6tisch-security-architectural-considerations-01 and I
have not seen any new technical argument being made on the list
(to my knowledge; it is very hard to absorb the entire sequence of
emails).
The main crux of the argument that was brought up to me privately
was that using a "well-known" key could be used as mechanism for
(very crude) filtering of the very first enrollment message. {This
is not necessarily a new argument and was discussed as "network
segregation" in
draft-struik-6tisch-security-architectural-considerations-01
(Section 1.2, #8.}
As already said, segmentation can be realized in many ways (having
an identifying string seems easiest). Besides, granularity at the
level of "6tisch-minimal15" does nothing to stop neighboring
networks {including those that may be poorly managed} to interfere
with one's own network, in case these both implement that spec
(this was the toy store vs. temperature sensor example, summarized
below:
/Tanya's Toy Town buys a couple of crates full of wireless
robot toys. They all use 15.4e, although not well. Each one
broadcasts an EB every second, and it includes all of the //
//same IEs that Charlie's temperature sensors expect. So
there are 400 correctly-formed 15.4e EBs per second arriving
from the store next door, and Charlie's sensors take //
//approximately six hours to join his network. /
While cryptographic keys indeed provide a mechanism for logically
partitioning the universe during operational use of a network, it
is not necessarily appropriate for filtering the very first
enrollment message (e.g., how does one know that the list below
will be the correct one in hindsight?). Network segregation is at
least partially a policy setting issue and should be dealt with as
part of flexible device management.
Quick question, though: if one would indeed use a well-known key
as network segregation mechanism (where each device implementing
802.15.4e-2012/TSCH and the IETF minimal draft uses as key K1 in
the beacon a string that is a function of "6tisch-minimal15") and
suppose the security considerations in
draft-struik-6tisch-security-architectural-considerations-01 are
considered not of interest,
a) How would one identify this key, using 802.15.4-2011?
The only way to potentially make this work would be to use a
9-octet key identifier field, where someone would reserve a
universal EUI-64 that could serve as globally unique "key source"
for the key "6tisch-minimal15". Who would this "someone" be?
Currently, this is not defined.
b) How would one store this key, using 802.15.4-2011?
The macKeyTable is supposed to contain cryptographic keys that can
only be written to this table, but not read (to prevent easy
exposure of supposedly secret keys). However, if one of those keys
is a well-known string, the behavioral semantics of I/O seems to
be jeopardized.
Wouldn't it be much better to put these issues to rest by *not*
mingling crude network segregation with key management issues and,
if one really wants to use filtering, simply pick a
"6tisch-minimal15" string and include this into an unsecured frame
as IE instead? {This would save a 9-octet key identifier,
headaches to specify missing pieces, such as key source, and
security concerns re side effects}. This network segregation
requires only a small IE (use header IE (see 5.2.4.2) unmanaged
information element (5.2.4.21)), e.g., by picking the 2-octet
Header IE = 0x00 (length=0, unmanaged id=0x00, IE content =
emptyst {to keep with the spirit of minimal}.
Rene
On 5/8/2015 9:25 AM, Rene Struik wrote:
Hi Jonathan:
It is always great to recount anecdotal evidence. However, I fail
to see why this should necessarily apply to 6tisch.
The question is what constitutes a proper mechanism for network
segregation. This technical topic was discussed in Section 1.2,
item #8 of the draft
draft-struik-6tisch-security-architectural-considerations-01,
where it was suggested that this relates to filtering based on
checking the "language of well-formed frames" (see 2nd starred
item in 1.2, #8). In fact, some of the language in that section
re IE header fields were from Kris Pister (see acknowledgement in
Section 3, p. 16).
Once again, may I suggest, as I did in my email of April 24,
2014, 9.47am EDT, to first read that draft and only bring up
topics not already dealt with there?
[excerpt email RS as of April 24, 2015, 9.47am EDT]
I did notice lots of emails surrounding 802.15.4 security (or
perceptions thereof), but I do not entirely understand the
background of these emails.
Since some emails seem to repeat similar discussions in December
2014 (including confusions and misconceptions of 802.15.4
security), I would like to encourage everyone to read the draft
draft-struik-6tisch-security-architectural-considerations-01
(posted January 9, 2015). I wrote this draft partially in the
hope that we would not have the very repeat of arguments we now
seem to witness. So, I highly recommended reading that 3 1/2
months old draft and only bring up topics not already dealt with
there.
Best regards,
Rene
On 5/7/2015 6:01 PM, Jonathan Simon wrote:
Once again I will repeat an old story…
We went to a Zigbee demo with our pre-WirelessHART product, which uses MICs to
authenticate both the equivalent of Beacons (called advertisements in WH) and
data traffic.
The Zigbee networks fell apart in our presence, while we operated fine. The
reason why was that the Zigbee networks did not use MICs, and were interpreting
some of our data traffic as coordinator realignment frames, causing their nodes
to change channel.
No protocol owns the airwaves - any protocol that does not anticipate random
frames arriving that look like valid instructions, and taking at least minimal
steps to avoid this problem (i.e. authenticating frames with SOME key), is
poorly designed.
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