certificate-transparency VS zlint

Recently I developed a presentation about immutability as a design concept in computer security. As part of it, I have slides which cover Certificate Transparency implementation[0], which uses Trillian[1] as a distributed ledger. Part of Trillian's documentation includes a Firmware Transparency[2] example. For the year or so I've been aware of it, I've thought that it's a great idea, and wondered if it would ever grow as a project/practice. Digging through the links in this announcement, it appears Trillian is the basis for the distributed ledger here. Glad to see the idea has been taken further by Google.

[0] https://certificate.transparency.dev/

[1] https://transparency.dev/

[2] https://github.com/google/trillian-examples/tree/master/bina...

> They could say that your certificate passes validation while, in fact, said security has been already tampered with on your side, giving your website's visitors a sense of false security.

This isn't how the Web PKI works. In order to tamper with your site's traffic, Let's Encrypt (or another CA) would need to issue another certificate for your site with a key that they (rather than you) control. This would be detected via CT[1], which your browser (unless it's Firefox) is already using

And note: by design, any CA in the trusted set can already do this, regardless of whether you use them or not. The things that are stopping them are that it's (1) not in their interest to do so, (2) it's detectable due to CT, and (3) would result in their root being hell-banned by the browsers.

[1]: https://certificate.transparency.dev/

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. Antitrust, 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?

My main source is Certificate Transparency, which is kind of a database of TLS certs created so far. But use external tools like Subfinder or Amass.

Certificates signed by reputable Certificate Authorities (CA's) are publicly logged by projects like googles certificate transparency, the EFF's SSL observatory and a few CA's directly, which can be viewed on websites like https://crt.sh/ and https://ui.ctsearch.entrust.com/. We will use screenshots of the latter service for readability, but you can verify the same information on the first service as well.

The one saving grace is that Certificate Transparency makes it so that false issuances are logged. CT is now required by the big 3 browser vendors. CAs caught wrongly issuing certs without good explanation have their CA cert(s) removed or revoked. (Though sometimes more slowly than I'd like.)

I'm not sure what you're talking about. I imagine you mean certificate transparency. Certificate transparency is not available on all browsers (FF doesn't support it), and only enables detectong issuance of malicious certificates/misbehaving CAs, but does not prevent the certificate being from being actually used. This means that a compromised CA could still issue malicious certificates and use them to attack many people before anyone notices it and the malicious certificates are revoked.

Yup, the two most popular are:

https://github.com/zmap/zlint

https://github.com/certlint/certlint

They each have their strengths and weaknesses, so CAs are advised to use both.

Can you compare it with https://github.com/zmap/zlint as a cert linter?