AMamiga386·Jun 15, 2023
You are correct: https://github.com/google/certificate-transparency/blob/mast...
You can embed CT attestations (SCTs) in the certificate itself, so yes, provided the CA is in cooperation with CT log operators, and deliberately does the pre-certificate -> SCTs -> real certificate dance, it is possible for a browser to validate embedded SCTs without an online check.
However, that assumes that the CA actively does that, they don't have to. Neither does the server. What's compelling them to is _policy_, set by Google and Apple, that their respective browsers won't accept certificates _without_ CT attestations. Google's policy specifically requires that one of the SCTs on a certificate must be a CT log run by Google. Google also controls the list of CT logs that Chrome will consider as valid CT logs, as part of deciding if an SCT is valid. Ant
Read the rest
itrust, anyone?
I was trying to make a similar point about Firefox - policy vs code. And rather than saying that it's specifically the CA/Browser Forum setting policy (which it does, but only baseline policy, which does not include CT), each org in the CA/Browser Forum has their own root cert inclusion program with their own policies, that all draw from baseline policy then add to it. You are right, _baseline_ policy does not require CT....
... and neither does _Mozilla's_ policy, now I've scanned through it. It actively acknowledges that CT exists (in that it mandates that if you issue a precertificate for CT, you _must_ issue the completed certificate), but it does _not_ require CAs to use CT. In stark contrast to Google and Apple.
Perhaps this is why they also don't implement CT checking in Firefox?