Earlier this year, an Iranian hacker broke into servers belonging to a reseller for certificate authority Comodo and issued himself a range of certificates for sites including Gmail, Hotmail, and Yahoo! Mail. With these certificates, he could eavesdrop on users of those mail providers, even if they use SSL to protect their mail sessions.

It's happened again. This time, Dutch certificate authority DigiNotar has issued a fraudulent certificate for google.com and all subdomains. As before, Gmail appears to be the target. The perpetrator also appears to be Iranian, with reports that the certificate has been used in the wild for man-in-the-middle attacks in that country. The certificate was issued on July 10th, and so could have been in use for several weeks prior to its discovery.

DigiNotar has revoked the certificate, which provides some protection to users (though many applications do not bother checking for revocations). However, the company has so far not disclosed how the certificate was issued in the first place, making it unclear that its integrity has been restored. As a result, Google and Mozilla have both made patches to Chrome and Firefox respectively that blacklist the entire certificate authority.

Microsoft says Windows Vista, Server 2008, 7, or Server 2008 R2, check Microsoft's online Certificate Trust List. The company has removed DigiNotar from this list, so Internet Explorer on those systems should already not trust the certificate. The company will issue a patch to remove it from Windows XP and Windows Server 2003.

DigiNotar's silence also means that little is known about the perpetrator. Responsibility for the Comodo hack was claimed by a person claiming to be an Iranian sympathetic with, but independent of, the country's government. This latest hack could just as well be another independent effort, or a government action.

The absolute trust given to certificate authorities, and the susceptibility of that trust to abuse, has long been considered a problem. We wrote about the problem in March, and there has been no material improvement in the situation since then. The certificate authorities remain a weak link in the entire public key infrastructure, and though cryptographic systems can be created that reduce this possibility, the scheme we have remains firmly entrenched, regardless of its flaws.

Update: DigiNotar's parent company, Vasco, has issued a statement about the issue. It claims that DigiNotar first detected a break-in on July 19th, and called in external auditors in response. DigiNotar and the auditors believed that the company had revoked all of the fraudulent certificates; however, "at least one" was apparently missed. An additional certificate has now been revoked. The statement does not rule out the possibility that there are other fraudulent certificates that haven't been revoked.