[SCITT] Re: Last Call: <draft-ietf-scitt-receipts-ccf-profile-04.txt> (CCF Profile for COSE Receipts) to Proposed Standard

[Henri Sirkkavaara <[e-mail]>]

All,

A correction to my own review of 4 September first. In finding 1 I listed n = 3, 5, 6, 7 and 11 as the sizes where the path bits decode to the wrong index. That enumeration is incomplete: 9 and 10 fail as well. Rechecking 2 through 11 against the definitions as written, every non-power-of-two size has at least one leaf that decodes wrong, and 2, 4 and 8 decode exactly. So the condition is that index recovery holds when the number of transactions is a power of two, and not otherwise.

Then one ask, and it sits where the thread already is rather than off to the side. This week has settled that the document's defect class is unnamed preimages: Nicholas on internal-evidence, Konrad's sentence binding the octets of the Signed Statement as registered, Anton's as-transmitted registering the same rule.

Finding 4 in my review is that defect one layer further out, and it is the largest instance in the document. Section 2.1 defines MTH over "a list of serialized transactions (as byte strings)" and gives MTH({d[0]}) = HASH(d[0]). Section 3.2 computes the leaf as HASH(internal-transaction-hash || HASH(internal-evidence) || data-hash). Nothing in the document says that d[i] is that concatenation. A builder working from 2.1 and a verifier working from 3.2 can produce different roots, and 2.1 is the definition that looks authoritative, because it is the one labelled Merkle Tree Hash.

If the group is naming preimages before this document leaves, that is the one to name.

On finding 1, I left the choice of remedy to the authors and will now say which I would take. Make the path length part of the decoding rule, or carry the index in the proof. Attaching the power-of-two condition to the sentence documents the hazard and leaves it in place, and an application whose author does not read that sentence still gets a wrong index and no error.

Still non-blocking, and my support for -04 as Proposed Standard stands.



On Saturday, September 5th, 2026 at 06:32, Nicholas Templeman <[e-mail]> wrote:

> Chairs, all,
> 
> Support for -04 as Proposed Standard, and one wording recommendation.
> 
> Konrad Gruszka's proposed sentence should replace the one I posted on 3 September,
> rather than sit alongside it:
> 
>   data-hash is HASH over the octets of the Signed Statement as registered, with the
>   unprotected header set to the empty map per RFC 9943 Section 6.3, over those octets as
>   registered, not over any re-serialisation of them.
> 
> Mine named the COSE_Sign1 tag because the tag was the axis in front of me. His binds the
> octets, which closes the tag, the outer array, and the next framing axis nobody has found.
> That matters because the space is combinatorial, not a list: re-emitting one Signed Statement
> under six CBOR encoding freedoms yields 64 legal encodings, 64 distinct data-hash values,
> none rejected by a stock parser, and 31 silently normalised back to the canonical form by the
> act of reading them. Enumerating framings cannot close that; binding the octets does.
> 
> Measurement, vectors and the script that recomputes them are published rather than restated
> here: https://councilof.ai/interop/scrapi-ccf/data-hash-framing-space.json
> 
> One note for the authors, no reply needed on-list: prior art exists for this rule.
> draft-mih-sokolov-scitt-payload-binding-02 §4.4 defines `as-transmitted` — "applies no
> canonicalization. The digest pre-image is the exact octet sequence already fixed by the
> container format or cryptographic envelope carrying the payload" — and marks both `jcs-n`
> (§4.2) and `cde-n` (§4.3) Withdrawn. That is Konrad's sentence as a registered algorithm, and
> it is worth the two not drifting.
> 
> Not blocking, and I was not blocking before.
> 
> Nicholas Templeman
> Council of AI (CSOAI Ltd)
> 
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Henri Sirkkavaara
Vaara - Runtime execution layer for AI agents
Built to see over the noise.
vaara.io
Helsinki, Finland