[Cbor] To be signed with packed CBOR

[Jim Schaad <[e-mail]>]

Brendan,

I know that this is currently an academic question, but something you said
in the SUIT meeting has me slightly worried.  The problem with being the
note taker is that you never have anytime to mentally go down the channels
of ideas that pop up.

One of the things that you said is that the use of packed CBOR would make
things better when there are multiple authentication structures on what is
basically the same data.  The problem is that if you do the packing prior to
doing the signature, then you end up in the situation where you need somehow
to also include the packing dictionary in the data that is being signed.  I
don't have enough knowledge of how the manifest works but if after a
signing, one can add more information to the manifest and then apply packing
to that section which could add more items to the packed lookup tables thus
breaking the signatures.  

All,

This is one of the reasons that I was asking questions about doing the
signature on a packed or unpacked version of the data.  The idea of adding
things which might alter the lookup tables at the root means that you have
problems knowing that what was signed is what is validated without doing
things like walking the content to extract a new pair of lookup tables to
include as part of the signed content.

Jim