On Wed, Oct 21, 2020 at 12:54:44PM -0700, Laurence Lundblade wrote:
> 
> > On Oct 21, 2020, at 10:58 AM, Benjamin Kaduk via Datatracker 
> > <[email protected]> wrote:
> > 
> >   x5t:  This header parameter provides the ability to identify an X.509
> >      certificate by a hash value.  The attribute is an array of two
> > 
> > I suggest using the word "thumbprint" somewhere to motivate the 't' in
> > "x5t”.
> 
> Using “thumbprint” makes sense to me, though it was changed from thumbprint 
> to fingerprint in March 
> <https://github.com/cose-wg/X509/commit/32c2bf2b2411250f6d9232b43ae0813ac9d88a44>.
>  

My point was more that we're effectively tied to the "x5t" symbol for JOSE
parity, and even if we want to call the thing it carries a "fingerprint",
we should still use the word "thumbprint" once to explain the mnemonic
value of the 't'.

> Is it the common understanding that this “x5t” identifies the end-entity cert 
> like subjectKeyIdentifier does for CMS 
> <https://tools.ietf.org/html/rfc5652#section-5.3>? I can’t imagine what else 
> it would identify, but it seems saying this explicitly would be helpful. CMS 
> certainly is explicit and detailed on this.

That's what I assumed, but probably worth a mention (one could, of course,
identify a CA by fingerprint as well).

> > 
> > Also, we may want to make a pass to check for consistent usage of
> > "attribute", "parameter", etc. -- I think this is the first time we say
> > "the attribute is”.
> 
> I believe the correct term is “header parameter”. This was settled on for 
> draft-ietf-cose-rfc8152bis-struct and Jim made a number of changes to 
> cose-x509 to use that term back in March (same PR as referenced above). 
> However, “attribute” is still used a lot and probably all those uses should 
> be “header parameter”.

That sounds right for everything except the -sender variants, which are
"header algorithm parameter"s.  (I had to look it up and check again while
reviewing the document.)

-Ben

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