[Suit] Ordering of elements in SUIT Manifest

[Brendan Moran <[e-mail]>]

Hi Ken,

I noticed your message in the meet echo chat; unfortunately, it wasn’t repeated at the mic and I missed it during the meeting.

> Related to the order of the manifest, I'm not convinced but I think the integrated elements should be before the suit-manifest because it would be referred by suit-install or suit-dependency-resolution section.

I think it is reasonable to say that elements the recipient requires should come before the elements the recipient does not require.

I also think it is reasonable to say that severable elements should come after non-severable elements.

But these are both “should” not “must.” So I don’t hold the opinion strongly.


Now as to the location of the integrated elements, I think I have to disagree. The problem is the order of operations:

When a constrained recipient receives a manifest, the first thing it encounters is delegation chains. This allows it to work down towards the public key that is in use. Next, it finds the authentication block. By now, it has the correct public key to validate the authentication block. The authentication block allows the constrained recipient to validate a single digest. Once it has done this, it can discard the authentication block (from memory anyway). It does not need to parse the authentication block again. Having parsed the authentication block, it has the expected hash of the manifest in memory. The next step it takes is to hash the manifest to verify/authenticate it. If this passes, then it can begin executing the manifest.

The constrained recipient won’t even know it needs an integrated element until after it has completed all these steps, so I am reluctant to put them first, since this would require random-access parsing of the manifest, rather than the linear process we have up to this point.

However, I’m happy to hear other opinions!

Regardless, the manifest now encodes integrated items with string keys, so it may well be that your CBOR encoder puts those before integers?

Best Regards,
Brendan
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