by Rik Ferguson

DigiNotar, where did our trust go?

Oct 17, 20115 mins
Security Software

The story that recently caused the biggest stir in IT security and government circles was the compromise at Dutch certificate authority DigiNotar and the subsequent “theft” of many important credentials. This event and related attacks at other Certificate Authorities, most notably Comodo, is of huge importance for internet users, governments and even the trust foundation that underlies the internet in general.
DigiNotaris a trusted authority. That means that they can issue certificates that allow websites offering secure, encrypted communications to prove that they are who they say they are. When you browse to your bank, your email provider or any other “secure” site, in the background these certificates are exchanged before encrypted communications can begin. Your web browser contains a list of “root” authorities whose certificates are trusted by default. If a web site presents a valid certificate and your browser is configured to trust the signing authority encrypted communications can begin, transparently to the end user. A valid certificate is one that matches the name of the site that is using it, that has an expiry date that has not yet been exceeded and critically is signed by a trusted authority. It is this last step that is normally difficult for those with malicious intent to overcome. DigiNotar’s security was compromised and a large number of fraudulent certificates were issued for services such as Google mail and Windows update.
The implications of this breach are serious. If an attacker can set up a proxy server, between you and your “secure” destination, the malicious proxy can pose as the real secure site. It can present the right credentials and the attacker can decrypt and read all your content, before passing it on, transparently, to the real final destination, a classic man-in-the-middle attack.
In a normal situation where you are browsing the internet you can connect directly from your computer to your secure destination, you are not at a great deal of risk. If however all my traffic must pass through a proxy, either at my Internet Service Provider or at state level, which is the case in some more restrictive nations then the risk increases. The proxy can make use of fraudulent certificates and act as a man-in-the-middle. There is also a risk on public networks such as Wi-Fi hotspots, where again the hot-spot provider will often use a proxy. Alternatively, an attacker could infect your system with malware that configures your computer to pass all traffic through a proxy of the attacker’s choice, wherever you are located. For this to be effective the attacker would need to be able to install code on your system to make these changes. At least one of the fraudulent certificates allows “code signing” meaning it can be used to certify that a program is from a valid publisher so this possibility certainly exists in theory and the booming cybercrime economy is proof positive that the means to deliver code to infect PCs are abundant.
The breach at DigiNotar is significant for a number of reasons. As a CA, DigiNotar’s entire business was built on a foundation of trust; they had a duty to ensure that the security and integrity of their systems was second-to-none. Certificates of this kind are used to secure the most sensitive of communications and allow online entities to assure their identities when dealing with customers. To say that these events and the earlier associated breach at Comodo have undermined trust in secure web transactions would certainly not be overstating the matter.
The failures were numerous:
•The first breaches were detected on the 19th July and yet hacker activity had been ongoing since June 17th. No public statement about fraudulent certificates was made until the press release of August 30th
•The fraudulent certificate was generated on July 10th and was actively used in Iran until August 29th when it was finally revoked.
•According to the report by Fox-IT many basic failures in securing processes and infrastructure were apparent, single AD domains, weak passwords, no anti-malware installed, lack of effective separation of critical networks and outdated or unpatched software on public-facing web servers.
Trust in all certificates issued by DigiNotar was revoked by most major browser and operating system manufacturers and the consequences for DigiNotar as a company were fatal, within two weeks, they were declared bankrupt at an estimated cost to the parent company of $3.3 to $4.8 million (US), excluding costs that may be incurred as a result of any claims that may arise.
The industry and other Certificate Authorities will need to ask some difficult questions now. When a relatively small group of organisations is trusted with assuring the identity of the rest of the web then an incident of this nature seriously undermines both public and professional confidence in the viability of the current system.
We should be promoting and enforcing regulatory standards for an industry of this level of importance. In much the same way that organisations who handle credit cards are required to conform to PCI standards; CAs should also conform to an audited minimum level of security. This would have eliminated many (hopefully all) of the failures listed above. By the same token there need to be standards set around rapid and effective disclosure in the event of a breach.
Looking to the future, I imagine we will move away from the model where a single client trusts a single CA and move more towards the model used by the backward compatible Convergence ( which can be configured to require a consensus of trust from multiple “notaries” before a certificate is considered valid.