It seems like every time someone tests airport security, airport security fails.
In tests between November 2001 and February 2002, screeners missed 70% of knives, 30% of guns and 60% of (fake) bombs. And recently, testers were able to smuggle bomb-making parts through airport security in 21 of 21 attempts. It makes you wonder why we are all putting our laptops in a separate bin and taking off our shoes.
The failure to detect bomb-making parts is easier to understand. Break up something into small enough parts, and it is going to slip past the screeners pretty easily. The explosive material will not show up on the metal detector, and the associated electronics can look benign when disassembled. This is not even a new problem. It is widely believed that the Chechen women who blew up the two Russian planes in August 2004 probably smuggled their bombs aboard the planes in pieces.
But guns and knives? That surprises most people.
Airport screeners have a difficult job, primarily because the human brain is not naturally adapted to the task. We are wired for visual pattern matching, and are great at picking out something we know to look for - for example, a lion in a sea of tall grass.
But we are much less adept at detecting random exceptions in uniform data. Faced with an endless stream of identical objects, the brain quickly concludes that everything is identical and there is no point in paying attention. By the time the exception comes around, the brain simply does not notice it. This psychological phenomenon is not just a problem in airport screening: It has been identified in inspections of all kinds, and is why casinos move their dealers around so often. The tasks are simply mind-numbing.
To make matters worse, the smuggler can try to exploit the system. He can position the weapons in his baggage just so. He can try to disguise them by adding other metal items to distract the screeners. He can disassemble bomb parts so they look nothing like bombs. Against a bored screener, he has the upper hand.
And, as has been pointed out again and again in essays on the ludicrousness of post-9/11 airport security, improvised weapons are a huge problem. A rock, a battery for a laptop, a belt, the extension handle off a wheeled suitcase, fishing line, the bare hands of someone who knows karate... the list goes on and on.
Technology can help. X-ray machines already randomly insert 'test' bags into the stream - keeping screeners more alert. Computer-enhanced displays are making it easier for screeners to find contraband items in luggage, and eventually the computers will be able to do most of the work. It makes sense: computers excel at boring repetitive tasks. They should do the quick sort, and let the screeners deal with the exceptions.
Sure, there will be a lot of false alarms, and some bad things will still get through. But it is better than the alternative.
And it is likely good enough. Remember the point of passenger screening. We are not trying to catch the clever, organised, well-funded terrorists. We are trying to catch the amateurs and the incompetent. We are trying to catch the unstable. We are trying to catch the copycats. These are all legitimate threats, and we are smart to defend against them. Against the professionals, we are just trying to add enough uncertainty into the system that they will choose other targets instead.
The terrorists' goals have nothing to do with aeroplanes; their goals are to cause terror. Blowing up an aeroplane is just a particular attack designed to achieve that goal. Aeroplanes deserve some additional security because they have catastrophic failure properties: if there is even a small explosion, everyone on the plane dies. But there is a diminishing return on investments in aeroplane security. If the terrorists switch targets from aeroplanes to shopping malls, we have not really solved the problem.
What that means is that a basic cursory screening is good enough. If I were investing in security, I would fund significant research into computer-assisted screening equipment for both checked and carry-on bags, but would not spend a lot of money on invasive screening procedures and secondary screening. I would much rather have well-trained security personnel wandering around the airport, both in and out of uniform, looking for suspicious actions.
When I travel in Europe, I never have to take my laptop out of its case or my shoes off my feet. Those governments have had far more experience with terrorism than the US government, and they know when passenger screening has reached the point of diminishing returns. (They also implemented checked-baggage security measures decades before the United States did - again recognising the real threat.)
And if I were investing in security, I would invest in intelligence and investigation. The best time to combat terrorism is before the terrorist tries to get on an aeroplane. The best countermeasures have value regardless of the nature of the terrorist plot or the particular terrorist target.
In some ways, if we are relying on airport screeners to prevent terrorism, it is already too late. After all, we cannot keep weapons out of prisons. How can we ever hope to keep them out of airports?
Bruce Schneier is the founder and CTO of Counterpane Internet Security. schneier@counterpane.com, http://www.counterpane.com
To subscribe to a free monthly newsletter providing summaries, analyses, insights and commentaries on security: computer and otherwise, visit http://www.schneier.com/crypto-gram.html
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