Re: [Ace] Design Consideration Document as one milestone?

[Hannes Tschofenig <[e-mail]>]

Hi Goeran,

you raise another difficult question that relates a bit to the type of
IoT devices have in mind. I fully agree with the challenge you
identified regarding symmetric vs. asymmetric key crypto. It will be
difficult to reach a consensus on that topic since most people in the
group are actually not building devices themselves and therefore just
use what fits their solution best.

The cost of transmission that you mention is also important but the
implication of just having fewer round-trips is a bit too simplistic
since a constrained resource server will obviously suffer a lot since he
has to listen for incoming connection attempts.

So, I fear that (while these are super important aspects) we will have a
hard time to make any useful decisions about them is two-fold:

 * We are not designing complete systems in the IETF and the energy
assumption relates to the overall system (rather than a single
protocol). Most of it is outside the IETF protocol design.

 * The processing capability obviously depends on the hardware and we
are not making any statement about hardware in the group. Looking at
Carsten's presentation from the BOF it also relates to cost, which is
again a very complicated topic since hardware cost is not the only cost
in product development.

The classes in the LWIG terminology document do not go into any level of
details regarding computational power and energy consumption. Only the
memory requirements are listed in more detail and they seem to be rather
hand-wavy.

Ciao
Hannes


On 03/13/2014 04:00 PM, Göran Selander wrote:
> Hi Hannes
> 
> Thanks for bringing this up. Let me give some context.
> 
> In the preparation for the BOF (and as was later shown in the BOF) it was
> clear that there are strong opinions about the (in)feasibility of /public
> key/ crypto in constrained devices. Some people state that ³there will
> only be two public key operations in the lifetime of this device²,
> referring to the high cost for asymmetric crypto so that they are only
> used to establishing secret keys that are used thereafter. Yet other
> people state ³the cost for public key crypto is negligable in today¹s
> devices² 
> 
> Looking into the literature it is clear that public key crypto is in many
> cases affordable, but also that it does not come for free. Moreover, when
> comparing e.g. with message transmission and reception in wireless
> embedded devices, you get another picture what may be expensive in
> security protocol execution from an energy consumption point of view.
> Section 3.2.2 discusses this in a symmetric crypto context.
> 
> This draft was put together in a rush a few days before cutoff and
> contains mainly obvious things. As said, I¹m happy to use this as a basis
> for a Wiki or restart the discussion. What I would like to see documented
> is the (non-obvious) cost comparisons  and trade-offs between e.g.
> round-trips and crypto operations, symmetric vs asymmetric operations etc.
> to be able to refer to in future discussions when we need to assess the
> feasibility of a particular security protocol in a constrained environment.
> 
> 
> Göran
> 
> 
> On 13/03/14 02:09, "Hannes Tschofenig" <[e-mail]> wrote:
> 
>> Goeran raised a question about adding a milestone for a document that
>> captures assumptions and design criteria.
>>
>> He contributed an initial version of such a document with
>> https://tools.ietf.org/html/draft-seitz-ace-design-considerations-00
>>
>> What does the rest of the group think about that idea?
>>
>> Would you be willing to review such a document?
>> Would you be willing to contribute to such a document?
>>
>> Ciao
>> Hannes
>>
> 
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