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CNET's error explaining DKIM

Declan McCullagh, writing in CNET, makes the standard schoolboy error of assuming that email sender authentication technologies are "antispam techniques."

They're not.

DomainKeys Identified Mail (DKIM) and other sender authentication technologies are simply ways to detect forgeries. At best, they give a partial indication whether a message is spam or not, but their main use is to allow recipients to look up the reputation of the sending domain.

Detecting phishing attacks via sender authentication depends on legitimate senders, such as PayPal, publishing information in the DNS. An email that purports to come from paypal.com can then be verified against that published information.

Of course, this doesn’t stop phishers from using similar domains, such as verify-paypal.com. Many users won't notice the difference. A DKIM test will "pass" because the bad actors own the fraudulent domain.

In other words, DKIM alone is almost useless. That's why we also need domain-level reputation services.

More at richij.com...

What People Are Saying

Richi, you are about 95%

Richi, you are about 95% correct. By itself DKIM is just authentication, and many people confuse that with authorization. As a real-world example, my driver's license may identify me but it says nothing about my driving record.

The 5% part is that we can fairly easily come up with a whitelist of the top few hundred phishing targets, with paypal.com at the top. This list is pretty static and can be of use today. This is a form of "reputation" (actually "accreditation"), albeit only of use to the largest players. But that usefulness encourages those sites to sign, which will encourage more sites to verify, which will increase demand for domain reputation, which will encourage even more sites to sign, etc.

As you say, we do need dynamic domain reputation services to realize the full potential of DKIM, and in particular to address the cousin domain problem. And although I believe DKIM will have impact on the spam problem, it will be indirect and will take longer.