Subject: Re: [6tisch] ANIMA vs. join process

From: "Turner, Randy" <[email-masked]>
Date: Fri, 22 May 2015 19:43:50 +0000

I don’t think we wait for a  complete solution from ANIMA , but I did like the 802.1AR bootstrap presentation that was given at the ANIMA meeting in Dallas – maybe there’s some ideas we could borrow.

It would be unfortunate if 6tisch and ANIMA come up with completely different ways of solving problems –

My $0.02
Randy

From: Rene Struik <[email-masked]<mailto:[email-masked]>>
Date: Friday, May 22, 2015 at 3:21 PM
To: Kris Pister <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>
Subject: Re: [6tisch] Shipping minimal

Hi Kris:

I tried to do this for the key "6tisch-minimal", but could not come up with something else than using a 9-octet key identifier and the need to define a key source and allocate a universal EUI-64. Hence, my question. BTW - I am not trying to be difficult here and simply ask how one could instantiate the 802.15.4-2011 and 802.15.4e-2012 specs so as to do what seems to be an approach you would favor.

I do know how one should be able to do this with a 2-octet header information element that seems to have the following properties:
a) it realizes crude network segregation (at granularity "6tisch-minimal") you aim for as well;
b) it saves (net) 6 octets in the enhanced beacon frame, with following breakdown:
    --- saves 8 octets in the auxiliary security header (1 octet vs. 9 octets for key identifier fields);
    --- costs 2 octets by including a 2-octet header information element (unmanaged header IE), with format 0x0000 {indicaing "6tisch-minimal");
    --- {this assumes EBs to be protected with a key}
c) it allows devices already in the network to synch their clock (using frame-based synchronization [assuming beaconing device as clock tower parent]).
d) it allows us not to have to worry about side effect of incoming frame security processing.

If all devices already have a pre-shared *cryptographic* key (that somehow got provisioned via out of band means and distributed only to devices that should be in the same network), they can still use the approach above, but do not need to include the 2-octet header IE as network segregation identifier. BTW - I did address an alternative mechanism to implement the "6tisch-minimal" network segregation issue, with metrics as above, not the strictly different problem of trying to pre-provision a pre-shared key via a work bench type approach.

Does this make sense?

Best regards, Rene

On 5/22/2015 2:36 PM, Kris Pister wrote:
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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