[Lake] CDDL in EDHOC RFC 9528

["Sipos, Brian J." <[e-mail]>]

All,

I have recently started work on an embedding of EDHOC which uses EAD to
negotiate some parameters along with the normal mutual authentication
sequencing. In doing so I have run into what it seems are typos in the CDDL
rules for EDHOC in Appendix C.2 [1]. Some of these seem like simple typos
and some are more complex. Two CDDL processing tools I'm trying to use are
both CLI, one from Rust crate [1] and one from a Ruby gem [2], so these and
the CDDL spec are my references for what is correct. I can write these up as
errata on RFC 9528 but want to check with the WG first.

 

The first set I ran into is the simple non-framed multiplicities for the EAD
similar t

    EAD_1 = 1* ead

where it seems like it should be of the form

    EAD_1 = (1* ead)

 

Another is the lack of a type within the `PLAINTEXT_2` group for the field
`C_R` which just seems like a simple omission.

 

Finally, there is the use of a type `map` within the ID_CRED_x fields, which
is not actually defined anywhere for CDDL. So I added a local definition

    map = #5

I'm not sure if that is the best way to handle this situation. Another
alternative would be something more CDDL-like

    { * any => any }

I don't think the two differ in what they will match but maybe the second
form is more tool-friendly?

 

As a suggestion for readability, I also think it's helpful to have a couple
of shared-type rules to make it obvious where different fields really do
share the same type. One for connection IDs (shared between `C_I` and `C_R`)
and one for credential IDs (shared between `ID_CRED_I` and `ID_CRED_R`) as
the following

    id_conn = bstr / -24..23

    id_cred = map / bstr / -24..23

 

Thanks for any feedback,

Brian S.

 

[1] https://www.rfc-editor.org/rfc/rfc9528.html#appendix-C.2

[2] https://crates.io/crates/cddl

[3] https://rubygems.org/gems/cddl