DigiNotar – why is Google special? – Tales from the Crypto

DigiNotar – why is Google special?

So, you’ve probably heard about the recent flap concerning a Dutch Certificate Authority, DigiNotar, who was apparently hacked into, allowing for the hackers to issue certificates for sites such as Yahoo, Mozilla and Tor.

I’ve been reading a few comments on this topic, and one thing just seems to stick out like a sore thumb.

DigiNotar’s servers issued over 200 fraudulent certificates. These certificates were revoked – but, as with all certificate revocations, you can’t really get a list of the names related to those revoked certificates to go back and see which sites you visited recently that you might want to reconsider. [You can only check to see if a certificate you’re offered matches one that was revoked.]

What behaviour would you reconsider on recently visited sites? Well, I’d start by changing my passwords at those sites, at the very least, perhaps even checking to make sure nobody had used my account in my stead.

But that’s not the thing that sticks out

What does stick out is that DigiNotar’s own certificate was removed from, well, just about everyone’s list of trusted root Certificate Authorities, once it was discovered that a fraudulent certificate in the name of *.google.com had been issued, and had not yet been revoked.

Yeah, given the title of my blog posting, I’m sure you could guess that this was the thing that I was concerned about.

So, why is Google so special?

I’m not sure I buy that DigiNotar’s removal from the trusted certificate list was simply because they failed to find one fraudulently issued certificate. It seems like, if that fraudulent certificate was for Joe Schmoe Electrical Repair, it would just have been revoked like all of the other certificates.

Removing a CA from the trusted list, after all, is pretty much going to kill that CA – every certificate ever issued by them will suddenly fail. All of their customers will have to install a new certificate, and what’s the chance those customers will go back to the CA that caused them a sudden outage to their secure web site?

So it’s not something that companies like Google, Microsoft, Mozilla, etc would do at the drop of a hat.

It certainly seems like Google is special.

The argument I would buy

There is an argument I would buy, but no one is making it. It goes something like this:

“Back in July, when we first discovered the fraudulent certificates, we had no evidence that anyone was using them in the wild, and the CRL publication schedule allowed us to quietly and easily render unusable the certificates we had discovered. Anyone visiting a fraudulent web site would simply have seen the usual certificate error.

“Then, when we discovered in August that there was still one undiscovered certificate, and it was being used in the wild, it was not appropriate to revoke the certificate, because the CRL publishing schedule wasn’t going to bring it to people’s desks in time to prevent them from being abused. So, we had to look for other ways to prevent people from being abused by this certificate.

“We could have trusted to OCSP, but it’s unlikely that the fraudulent certificate pointed to a valid OCSP server. Besides, the use of a fraudulent certificate pretty much requires that you are a man-in-the-middle and can redirect your target to any site you like.

“We could have added this certificate to the ‘untrusted’ certificate list, but only Microsoft has a way to quickly publish that – the other browser and app vendors have to release new versions of their software, because they have a hard coded untrusted certificates list.

“And maybe there’s another certificate – or pile of certificates – that we missed.

“So we chose, in the interests of securing the Internet, and at the risk of adversely affecting valid customers, we chose to remove this one certificate authority from everyone’s list of trusted roots.”

I’ve indented that as if it’s a quote, but as I said, this is an argument that no one is making. So it’s just a fantasy quote.

Is there another possible argument I might be missing, but willing to accept?

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