[ 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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