SSL certificates have been in the news lately (again), and there’s a huge uproar. Is SSL still OK? Is PKI dead?
While most people understand the technical side of PKI, I’ve found that the “soft”, or what I call the “political” side, is not as well understood.
Anyone can set up the technical infrastructure to become a CA – but what makes the Root CAs found in your browser special? And as a corollary, how do you get into that select list? Each company officially has their own method of determining what CAs are in their list of Trusted Roots. Mozilla clearly outlines their requirements on their wiki, and Microsoft has a program for inclusion. In general, there are a few technical requirements, and “the audit” – usually a WebTrust audit. I’ve audited CAs (not a WebTrust audit), and what you look for is compliance with the stated policies. However, the stated policies might not be the best option for a Root CA. WebTrust just requires that
“Subscriber information was properly authenticated (for the registration activities performed by ABC-CA).
The integrity of keys and certificates it manages is established and protected throughout their life cycles.” (http://www.webtrust.org/item27804.pdf)
So, what is “protected”, what’s “properly authenticated?” That’s left up to the CA to decide. As long as the CP and CPS cover what the CA is doing, how they’re doing it, and the auditor thinks it’s “protected” or “properly authenticated”, it’ll pass the audit. Generally, once the audit is passed, it’s almost trivial to get into the operating systems and browsers – just a paperwork exercise.
In the case of Diginotar, we can assume they’ve had a recent audit (not necessarily WebTrust) because they’re in Windows and Firefox (NSS), and the auditor felt that they were “secure” enough. Something went wrong though in the subscriber identity proofing process (if it even happened). The CA is just a tool, it can enforce some policies, but not all – it has no clue that the people requesting the certificate for *.google.com are not really Google – the RA function checks that then instructs the CA to issue the certificate(s). If the RA function was bypassed (intrusion into the CA), then the CA will do as it’s told and issue the certificates.
Ideally, CAs have an off-line root CA – no network connection, generally turned off, and only able to be turned on by the folks who have control of the CA. This is the Root CA that is in the operating systems and browsers. Then, that Root can revoke its sub-CA certificates, and life moves on (except for folks who now have to get a new certificate), and most people won’t even know. When an on-line root is compromised, it’s a bigger deal for everyone involved to revoke that CA – patches are issued, instructions go out on how to delete it or distrust it, etc.
Most people blindly trust the Root CAs in their browser/operating system – have you looked at the list in your OS/browser of choice? Do you know anything about these CAs or are you trusting the folks at Mozilla, Apple, and Microsoft to tell you if they’re to be trusted?