“In the hurly-burly and the infinite variety of travel, you can end up with nonsensical results in which the T.S.A. person says, ‘Well, I’m just following the rules,’” Mr. Hawley said. “But if you have an enemy who is going to study your technology and your process, and if you have something they can figure out a way to get around, and they’re always figuring, then you have designed in a vulnerability.”