DigiNotar fail: “this time is different”

Incompetent certificate authorities endangering users with fraudulent certificates is nothing new. There have even been allegations of willful corruption, including accusations that at least one CA is a front for the Chinese government, a nation not exactly known for following due process when it comes to intercepting communications. From that perspective, the DigiNotar debacle would have been yet another anecdote in the growing repertoire of inept CA stories. Yet there were a few notable aspects to the incident that truly made this one different, and perhaps a welcome sign that the situation is improving.

First it was caught by end users because  of a feature in Chrome that “pins” root certificates for Google properties. This is surprising: a man-in-the-middle attack against SSL, armed with a valid certificate from a trusted issuer used to be transparent for all intents and purposes. After all, CAs are interchangeable: it does not matter whether Verisign or Honest Achmed issued the certificate for GMail– to the web browser they are equally trusted. This is great news for attackers; even if your website obtains its certificates from a semi-competent CA, they can simply go after any one of the remaining 100+ issuers in order to successfully impersonate your company. Root-pinning in Chrome is an experimental feature to mitigate this risk. It is not based on any standard, although it can be viewed as an extension to HTTP Strict Transport Security (HSTS): in addition to asserting that a website is available over SSL only, the website can assert that it only sources certificates from a small number of root CAs, working around the weakest-link-in-the-chain problem alluded to above. At least that is the idea; as implemented currently, this list of pinned websites is hard-coded into the Chrome web-browser source code. Sites can only take advantage of this by submitting a request to Google to get added to that whitelist. This is clearly a model that will not scale long term.

But we digress– the other surprise in this debacle was the swift response from Mozilla– who maintains the Firefox web browser– and Microsoft. In the past, cases of “mistaken identity” were dealt with by individually blacklisting the issued certificates. In the case of Windows such certificates are usually these are shipped as part of a monthly security update, because revocation checking can be unreliable. For example a look at the certificate store on a Windows 7 installation shows about a dozen certificates marked “untrusted,” including those impersonating Microsoft, Google, Skype, Yahoo and Mozilla.

What about the CAs responsible for these mistakes? They are still in business, hopefully more enlightened from the experience and following more stringent identity checks procedures. But they are still listed as a trusted authority by Windows and Mozilla. Revoking that privilege must have seemed unthinkable: all certificates issued by that particular CA would be instantly invalidated. Any user trying to connect to a website using such a certificate would get an ominous error message displayed by their web browser, designed to be difficult to work around. Imagine the confusion and user-support costs if this were done for Verisign, one of the largest issuers on the planet. Even for a CA with relatively small market share (“UTN-USERFirst-Hardware”– responsible for a batch of fraudulent certificates, note the delicious irony in the name of putting users first) there is the risk that the offending CA may get upset (read: litigous) and go after MSFT for this affront to their self-esteem. The inherent asymmetry in resources makes this a difficult position for MSFT: they have deep pockets and very large market share, it would be easy to paint this as a case of big-bad Microsoft effectively putting a struggling CA out of business. With tortious interference claims and hefty damages on one side, and an unappreciative press on the other side, it hardly seemed worth it to begin this fight.

Except that in the case of DigiNotar the unthinkable happened: first Mozilla and then Microsoft removed DigiNotar from its trusted roots. Mozilla prefaced their argument with: “… because the extent of the mis-issuance is not clear…” For the first time this reflects a conservative approach lacking in past incidents. Before it was the norm to assume that fraudulent certificates were isolated mistakes and unlucky days for an otherwise sound CA– this time neither Mozilla nor MSFT were willing to take that on faith, and instead removed the CA altogether. (Incidentally Chrome uses the system roots on Windows and NSS roots on other operating systems, effectively inheriting both of these.)

Apparently once the ineptitude reaches an egregious level, even certificate authorities face the consequences. Except that the “consequences” in this case are not of a financial nature: VASCO, the parent company, helpfully notes in their press release for the security incident that they “expects that the cost of [helping existing customers] will be minimal” and “… the first six months of 2011, revenue from the SSL and EVSSL business was less than Euro 100,000.” In other words, complete loss of the CA business due to gross negligence presents no serious risk to the company– even as their actions endangered the privacy of users around the world.


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