Hi Laurence,

From: Laurence Lundblade <[email protected]>
Date: Thursday, 23 July 2026 at 04:00


The point is to remove mention of C509CertData from the paragraph discussing 
c5t because it has nothing to do with c5t. A c5t is a COSE_CertHash, an array 
of 2 with a hash algorithm ID and a bstr containing the hash. If you are 
sending or receiving a c5t, you are not using C509CertData at all.

The mention of C509CertData makes one think that maybe you should bstr wrap the 
C509Certificate before hashing. It leaves one trying to figure out why it is 
mentioned. (I suppose I may be missing something, but I couldn’t come up with 
any reason that it would be mentioned).

[GS:] OK, I see. I found one occurrence where C509CertData is mentioned while 
talking about c5t, and that sentence is not necessary so we can just remove it:

OLD
The value type of c5t is the COSE_CertHash structure defined in [RFC9360], 
which contains the hash value of the C509 certificate calculated over 
C509Certificate. Thus, C509CertData contains all data necessary to calculate 
the thumbprint c5t.
NEW
The value type of c5t is the COSE_CertHash structure defined in [RFC9360], 
which contains the hash value of the C509 certificate calculated over 
C509Certificate.

Thanks for pointing this out. The change is now included in 
PR#401<https://github.com/cose-wg/CBOR-certificates/pull/401/changes>.

Göran

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