Re: [Lake] Ways forward on MTI cipher suite text

[Russ Housley <[e-mail]>]

I would prefer to see one MTI (Option 2).  I can live with that MIT being 0/1 or 2/3, and I have a mild preference for 2/3.

Russ


> On Jan 20, 2022, at 12:03 PM, Mališa Vučinić <[e-mail]> wrote:
> 
> Dear all,
> 
> During the last LAKE interim meeting, we discussed the issue
> of an MTI cipher suite and we agreed for the chairs to open a
> thread on the subject. As a reminder, the previous discussion
> points on this topic are summarized in github [1] and in
> John’s mail dated 13 May 2021 [2].
> 
> We’d like to see if there is rough consensus in the WG on
> this topic, at this moment in time. Knowing that the formal
> analysis of the EDHOC-12 specification is under way, we
> should keep in mind that additional input may arrive down the
> road from teams working in the computational model.
> 
> As a reminder, the most recently discussed text for this
> is in a PR [3] and states:
> 
> “For many constrained IoT devices it is problematic to support several crypto primitives. Existing devices can be expected to support either ECDSA or EdDSA. Cipher suites 0 (AES-CCM-16-64-128, SHA-256, 8, X25519, EdDSA, AES-CCM-16-64-128, SHA-256) and 1 (AES-CCM-16-128-128, SHA-256, 16, X25519, EdDSA, AES-CCM-16-64-128, SHA-256) only differ in size of the MAC length, so supporting one or both of these is no essential difference. Similarly for cipher suites 2 (AES-CCM-16-64-128, SHA-256, 8, P-256, ES256, AES-CCM-16-64-128, SHA-256) and 3 (AES-CCM-16-128-128, SHA-256, 16, P-256, ES256, AES-CCM-16-64-128, SHA-256). To enable as much interoperability as possible, less constrained devices SHOULD implement all four cipher suites 0-3. Constrained endpoints SHOULD implement cipher suites 0 and 1, or cipher suites 2 and 3. Implementations only need to implement the algorithms needed for their supported methods.”
> 
> The options we see at this moment in time are:
> 
> Option 1: Keep current text as-is unless/until more feedback
> is provided that motivates re-opening this issue
> Option 2: Proceed with selecting a single MTI cipher suite
> 
> We'd like to know if the WG can live with Option 1. Note that
> doesn't mean you think option 1 is perfect, just that it's
> something with which you can live. If you prefer option 2 or
> some other option please suggest specific text.
> 
> Mališa and Stephen
> 
> [1] https://github.com/lake-wg/edhoc/issues/22
> [2] https://mailarchive.ietf.org/arch/msg/lake/75nRaD6czYG6RqLT06Qe8C_lsaM/
> [3] https://github.com/lake-wg/edhoc/pull/225/files