Obscure Attack Threatens Privacy, e-Commerce

on September 1, 2011
Reading Time: 2 minutes

An attack on a Dutch company in the obscure–to most of us–business of issuing digital certificates poses a serious challenge to secure web communications. No, you shouldn’t stop using Amazon.com or Gmail, but the attack opens another front in the never-ending war that threatens the security of the internet. The tale is a bit complicated, but I’ll try to make it simple. (And thanks to Swa Frantzen of the SANS Internet Storm Center for his detailed analysis of the incident.)

Since the early days of the the secure hypertext transfer protocol (https) has been used to lock down communications between browsers and web servers. Its use is indicated by the letters “https” in the URL, often a locked browser icon, and sometimes the use of green text in the address bar (screen shot above shows Google’s Chrome browser connected to a secure site.)

Https depends on something called a digital certificate that is supposed to do two things. First, your browser checks the certificate for proof that the server it is connecting to is what it claims to be, that is, it asks the server to present a digital ID card proving that it really is mail.google.com. Second, the certificate includes a key that is used to set up encryption of the traffic between the server and the browser.

All of this, obviously, depends on the integrity of the certificate. Some time in the past–just when is not certain yet–unknown parties breached the system of DigiNotar, a Dutch certificate authority. The attackers issued a number of fake certificates in July. On July 19, DigNotar discovered the attack an revoked a number of certificates. However at least one, for google.com, was missed. This fake certificate was used to connect users, mostly in Iran, to a fake Google site.

All of this had little immediate effect on anyone outside Iran. Microsoft, Mozilla, and Google updated their browsers so that they will no longer automatically trust any certificate issued by DigiNotar (the situation with Safari on Macs is more complicated.) This is a problem for DigiNotar and its legitimate customers, but is the best way to protect everyone else.

Furthermore, the fake certificates were only a problem if users were also directed to a fake site. This required a separate attack on the internet’s domain name system (DNS) to replace the legitimate addresses of Google servers with fake ones. That is why the attack only affected users of Iranian DNS services. (There’s only speculation at this point on why Iran,  but one possibility is that the attack was designed to allow the country’s security services to read what users thought were secure, encrypted communications with gmail and other Google services.)

Still, this is another serious warning shot telling us that major improvements are needed in internet security. Attacks redirecting traffic to fake web sites, either by compromising DNS servers or through a technique known as DNS cache poisoning, are not rare. When combined with undetected fake certificates, they have the potential to be devastating.

One obvious area for improvement is the certificate authority infrastructure. As it exists, the certificate authority is what engineers call a single point of failure. Compromise it and the entire security system, which ultimately runs on trust, fails. In particular, a speedy investigation is needed into how the audit trhat followed DigiNotar’s discovery of the breach failed to find the fake Google certificate.