Subject: Re: [TLS] New Version Notification for draft-kampanakis-tls-scas-latest-00.txt (ICA Supression)

From: Bas Westerbaan <[email-masked]>
Date: Thu, 17 Mar 2022 15:13:10 +0100

To get a sense for the size and possible issues with a list of
intermediates, I had a look at the intermediates in Certificate
Transparency. Let me stress that there are many caveats and I certainly do
not wish to suggest that this is the method to compile such a list of
intermediates.

Februari 20th, I downloaded all submissions from the CT logs
{nimbus,nessie,yeti,argon,xenon,oak}202[23], sabre and oak. Recall that
certificates are submitted to certificate transparency with a
certificate chain. Notably missing are skydiver and digicert CT1, which
have about 10m and 1m unexpired certificates each.

I found 43,280 unique intermediates. The vast majority are by browsers
untrusted intermediates used by Google for test submissions to check for
maximum-merge-delay (MMD) violations on CT logs.

For each non-MMD intermediate I recorded the latest expiring certificate,
the *example*, signed by the intermediate and submitted as such to the CT
logs, provided the certificate hasn't expired (Feb. 20th), is already valid
and has server authentication EKU.

That yields 910 intermediates.

By design CT logs are less strict about validation than browsers (the goal
is to record issuance — not check it.) Because of this expired/revoked
intermediates, there are certificates that are no longer valid with the
chain they were submitted with. Others would have never been accepted by
any browser to begin with.

For each example I verified the original chain (using the union of all
roots accepted by the CT logs.) If that didn't work, I tried to build a
chain using the other intermediates from CT which might not have popped up
earlier. Adding those and removing those that didn't work out, leaves us
with 902 intermediates.

Those account for 1,838,205,562 submissions, (here a certificate is counted
as many times as it has been submitted) although I did only check the
single example certificate

For 91,540 submissions (0.05%) I could not verify the example (for various
reasons.) For the majority of those the intermediate seemed valid, except
for 2,602 submissions.

I ignored policy constraints.

Please find details per certificate in the attached log. Hashes are sha256.

Best,

 Bas