Re: [Cose] Key management for MACs (was Re: Review of draft-schaad-cose-msg-01)

[Hannes Tschofenig <[e-mail]>]

> Particularly for constrained devices, it is unlikely that applications
> will want to pay the performance penalty of generating and encrypting a
> key management key to perform a MAC operation.  Heck, they may not have
> credible random number generation in the first place!  And they are
> likewise unlikely to want to pay the message size penalty of carrying
> the encrypted key.

It would be good to know what devices you have in mind in this discussion.

I personally don't think we should target devices that cannot even do
key management for symmetric cryptography. I would even argue that we
should aim for devices that support a random number generator and are
also able to do public key crypto.

We are not doing ourselves a flavor if we place artificial constraints
on our protocols that make them pretty insecure in practice. We already
have enough insecure IoT devices in the market.

Here is the slide deck I presented in the LWIG group at the last IETF
meeting; it explains the performance of state-of-the-art crypto on
common Cortex M class MCUs.
https://www.ietf.org/proceedings/92/slides/slides-92-lwig-3.pdf

Ciao
Hannes