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Comment by kmowery | Hacker News Reader

Hi! Lead author here.

We'll be giving a talk on this work tomorrow at the USENIX Security conference, but I'd be happy to answer questions here before then!

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Good luck catching your flight :-)

What were some of the challenges of carrying out these tests? And I imagine procuring the machine may have been an issue if the manufacturers knew you were exposing their shortfalls.

You'd be surprised how difficult it was to bring it on campus and actually turn it on! Over the course of the project, we worked with our IRB, radiological safety experts, regulatory compliance, and campus public safety before we put someone in front of the device. We set the machine up in a lab with a concrete wall to backstop the radiation, and had a 2 meter safety zone around it while it was actually emitting X-rays.

As for procurement, we purchased our machine on eBay from a private seller who purchased it from a U.S. government surplus auction.

You're saying that compliance with university radiation safety protocols was difficult -- for a machine that has been installed around the county and used to expose millions of passengers? I think that's a big part of the story.

Not unless the weirdnesses of ethics panels is part of the story.

Jon Corbett here. Thanks for conducting this study. For some, watching a video of me beating the scanners isn't enough to prove it, but it becomes harder to ignore when a scientific study confirms it. It's also nice to see confirmation of the "pancake exploit" which those critical of the machines have suspected for years.

Hi,

Have you tried concealing things under a couple of inches of a biological material and wrapping that to the body (beer gut, pregnant lady)?

Specifically, I'm thinking a a few large chunks of ham, coupled with some transglutaminase to aid in the forming of a "meat shield".

Yes we did! Any organic material shows up pretty well under backscatter X-ray, and so can be used to cover darker contraband. You can see this done with Teflon in our gallery: https://www.radsec.org/gallery.html under "Concealing a Knife by Masking".

We didn't try meat due to the mess, but it would almost certainly work as well!

(Technically, in this X-ray energy spectrum, the amount of backscatter is related to the "effective Z" of the material, where Z is the atomic number of the elements involved. Materials made from lighter elements like carbon and oxygen? Backscatters well. Heavy elements like iron? Absorbs x-rays.)

Yeah, I guess I thought they might have something a bit more spectographically advanced to determine molecular makeup rather than just backscatter (something that might distinguish teflon with it's abundance of fluorine from organic matter). It seems like a much more crude instrument than I thought.

For millimeter wave, I'm pretty sure the teflon wouldn't work though, since the millimeter wave machines are likely tuned for organic makeup rather than just backscatter.

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