Understanding the first imperative of a commercial Certificate Authority

> So, I'm not sure that it's strictly true that commercial CAs will refuse to do anything that cannibalizes their own sales.

Someone (ie. some CA) had to cross-sign Letsencrypt root certificate (or its direct derivative). Turns out that CA is IdenTrust, a bank consortium. [1]

I'm not disagreeing its a good rule of thumb though.

[1] https://en.wikipedia.org/wiki/Let's_Encrypt#Technology

Audit ought correctly to be a last resort, we should only audit things because the superior options were impractical (or outright impossible). Auditors are invariably conflicted (not giving a clean audit is bad for business) and other actors must work to mitigate this problem.

Part of the failure of Symantec (causing them to exit the CA business last year as a result of financial pressure) was that rather than having in place their own effective oversight they had increasingly relied upon audits from the Big Four to confirm that things were being done correctly at their "partner" companies, even though the wider PKI community had seen repeatedly that audit is not very effective and should not be a substitute for oversight roles.

As a result when problems with CrossCert were identified, Symantec found they didn't have the records that ought to have existed, and ended up asking CrossCert for them, of course CrossCert did not have such records. This situation couldn't have happened if Symantec had effective oversight, since necessarily this oversight role would examine the (non-existent) records.

Individual audit companies may prove either incompetent or corrupt too. Mozilla concluded that the Hong Kong EY (Once "Ernst and Young" but short names are cool now apparently) was either incompetent or corrupt and told its parent that it will no longer accept audits from this outfit. This was part of the problem with StartCom, their audits don't mention things that should have been evident at the time to a competent auditor.

A central purpose of Certificate Transparency is to reduce the need to rely on auditors. With all the signed certificates made public, independent researchers can interrogate data once only accessible to auditors. For example, the question "Were any certificates issued for Debian Weak Keys?" is something we might once have resolved with audit - let's ask the CA "Do you check for weak Debian keys?" and if they say "Yes" that's a pass. But today researchers can simply download all the public keys, and memcmp() them against Debian Weak Keys. Upon finding one, they raise it as a Problem Report. Sure enough the CA discovers that although of course they believed they were checking for these weak keys, for a brief period the check was disabled and they issued a certificate. Oops. Observatory tools like Censys might have helped, but Certificate Transparency gives us guaranteed coverage.

Nevertheless, audit is a necessity for some practical questions. Auditors physically visiting a facility can verify that it is indeed physically secure (are the data centre fire doors left open onto a shopping centre car park?) and that documentation physically exists (are there, in fact, binders full of procedures? It's funny, when they know nobody follows the procedures humans are often too lazy to even bother writing them down...). Likewise auditors must attend certain ceremonies e.g. to create a new private key. It would be very expensive for representatives from the major Public Trust Stores to be sent around the world to do this, and it's clearly not acceptable to just insist that all CAs must be physically located in Northern California.

The central thesis of the article seems to reject all market forces that aren’t directly controlled by the CA. For starters, CAs have to compete to maintain the trust of the browsers. The author glosses over this as if it’s barley relevant, but the browsers essentially decide whether CAs are allowed to conduct business at all. CAs also have to compete for the trust of their customers. The author seems to think that CAs publishing a bit of fud somehow entirely negates the customers ability to assess their trustworthiness. I’d say that any actor who makes decisions about trust based only on marketing content probably doesn’t care very much about the integrity of the CA system. The existence of commercial insentive doesn’t intrinsically make a system corrupt. The CAs product is essentially trust, if their product isn’t good enough, then they won’t be able to sell it. Especially since there’s a number of different supervising bodies to ensure they’re doing a sufficient job.