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Body Scanners at BUD


Note: I wrote this post in the departures lounge at BUD, but it was not posted online until the 25th when I was back home.


I’m really not liking air travel. It makes me ridiculously uncomfortable. Really only one part of it though: security.

Since the introduction of the body scanners in airports, as I have something of an understanding of how they operate, going through security is a pretty terrifying prospect for me. I think that over time it’s got worse too.

My primary objection to them is that in order to function, they necessarily use radio waves that penetrate clothing (what would be the point of them otherwise?) and develop a 3D model of your naked body. Of course, try and put this point of view to the staff and you may get called a liar.

Two airports that have been consistently excellent at dealing with my wish to opt-out of this humiliating and degrading process: AMS and FRA. If you are flying in Europe and you need to go through an airport on the way, then these are my best experiences.

Airports that have been the worst are the London airports. They were so bad that I actually haven’t flown through a London airport since 32c3. Maybe they have improved now, but I’m not holding out much hope.

Despite the fact that you can opt-out of the process there have been two disturbing developments that worry me. One is computer vision. You might notice that in security you are checked without linkage to your identity documents or boarding pass (although depending on the time of day your anonymity set size may vary) and so even if these machines were storing these nude models of everyone going through they are not immediately linkable.

There are assumptions that only hold as long as we also assume that technology will never advance. Policy needs to consider likely futures where things are possible that are not possible today.

Facebook and other companies have been working on face recognition and have large databases of user photos. They even convinced users to tag the photos to provide training data for their facial recognition systems. If one of these machines is accidentally left in debug mode and a large set of these models gets leaked then we’re not that far away technically from identifying each and every person in that set. This could be used for blackmail or just to publicly embarrass someone.

The second development is what has prompted me to write this blog post today. It’s about the layout of the security area. I would have taken a photo but when an ordinary person tries to document such a thing it is considered “hostile reconnaissance” and I didn’t want to have any trouble there. Instead, here is a rough diagram:

   |x|  v  |x|
   |r|  v  |r|
   |a|  v  |a|
   |y|-|v|-|y| Metal Detector
   | |  v  | |
   |b|  v  |b|
   |e||>v<||e| Body Scanner
   |l|  v  |l|
   |t|  v  |t|

You’ll notice that whether you opt-out or not you still have to walk through the scanner. All you have to go on is that the light is yellow and not green meaning the scanner is off probably maybe unless I’ve not worked out how the lights work.

I hunched over and ran through it. It was a horrifying experience for me and probably I won’t be coming to this airport again. This is a reminder though that this technology isn’t going away and all the time we are getting closer to just having standoff millimeter wave cameras (which already exist by the way - they just need to be made a bit smaller) with clothes penetrating vision ubiquitously deployed anywhere we currently have CCTV. It will be the new “high definition” or “night vision”.

While TSA and airlines may use the “Automated Threat Detection” (ATD) software there is nothing that technically prevents others from not using it, and that data with the nude image still exists for the ATD software to process.


For more horrifying thoughts about what might happen in the future when the technology catches up, I recommend watching Charles Stross’ talk from 34c3: Dude, you broke the future!.


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