Re: [TLS] ct_compliant cached info field

[Martin Thomson <[e-mail]>]

On Fri, Dec 28, 2018, at 04:58, Eric Rescorla wrote:
> Please take a look at
> https://tools.ietf.org/html/draft-ietf-trans-rfc6962-bis-30#section-6.5

At a minimum, this would seem to update cached_info.

There's not a lot of meat on this text.  It seems to be saying that if you are providing transparency_info, then you can provide a certificate other than any of the certificates that the client believes to be CT compliant.  Also, you don't provide "x509_sct_v2" or "precert_sct_v2" in transparency_info.

How is the client then able to determine that this new certificate is CT compliant?  Using  "inclusion_proof_v2" and "signed_tree_head_v2" (or one or other)?  If so, the text doesn't point in that direction.

There's a lot of "why" missing in this document.  Why would a client choose to indicate "ct_compliant"?  Why is cached_info being extended in this way?

I might guess that the reason here is that the draft aims to avoid including information that might change over time, which would render caches invalid.  Isn't that motivation to recommend an SCT over an STH?

Separately, why does this establish a new registry for signature schemes?  It is obviously trying to keep TLS compatibility, based on the codepoints, but forking the registry is a great way to create problems.