When PGP signatures can be misleading
The trust that PGP signatures generates can be deceptive, one researcher, a regular poster to the full-disclosure vulnerability mailing list, has discovered.
Gadi Evron, an information security researcher based in Israel, generally signs his posts to the list with his PGP signature, due to the fact that his email address is constantly used by spammers. Anyone who wants to verify an signed email is actually from the person claiming to send it, can do so.
What he did not reckon was that someone would try to use his PGP signature inside a spam email to impersonate him.
Ironically, the spammer in question copied his PGP signature from a message which he had sent on May 1 - about a new mailing list he had created called Spam Research.
Of course, in this case if anyone had verified the signature, he or she would have known that it did not belong to the sender.
On May 26, Evron received an email from a developer who is part of the Debian GNU/Linux project who informed him about a spam message he (the developer) had received that got through his filters.
Upon further examination the developer discovered a PGP signature. Using Google he quickly found the post which the signature originally belonged to.
"Spammers have been known for a while now to use PGP signed messages to get through spam filters. Although some spam filters mark PGP messages as a higher risk of being spam, most would give signed messages a better chance of being legitimate email messages," Evron wrote in an essay detailing his experience.
"Signing messages with self-created legitimate keys is risky. Forging a PGP signed message is time consuming and more difficult than just ripping one. Spammers usually search Google for the very first signed message they can find online and copy the text of the signature," he said.
