Mark Seiden gave a great talk on physical security. He believes digital security is superior to physical security, as physical security is dominated by people who believe obscurity is a legitimate way to achieve security. As a result, only criminals and locksmiths know which systems work, and the public is left vulnerable. Several years a group called Anti Security tried promoting a "closed source" movement. Their web site was down today but you can see an archive. (Incidentally, Matt Blaze's research created a firestorm in the physical security community.) Five years ago, Mark discovered a vulnerability in security systems used in airports, which "could enable terrorists to gain control of the electronic
badges that allow employees with security clearance to enter and
leave restricted areas."