Why Is the TSA Scanning Paper? | Hacker News Reader

Why Is the TSA Scanning Paper?

schneier.com

173 pointspavel_lishin124 comments

My guess, already voiced by "Ron" on Schneier's blog: they're looking for nitrocellulose. Nitrated paper is not obviously different in appearance from ordinary paper. Sheets of nitrocellulose have negligible vapor pressure and little dust so they could be missed by other means like the "puffer" detectors.

If they're putting these materials through a separate machine my guess would be another detector based on optical spectroscopy - maybe Raman? Something like that. It wasn't clear from the article whether the paper products in their separate bin just went through the same inspection chute as everything else.

Agreed. IMO the other plausible theory is disguising a bladed weapon of some kind in stacks of paper. The rest of the speculation appears to be based on misinterpretations of the headlines (scanning vs X-ray).

They're not putting them through a different detector, though. They take out the books and all papers the passenger has, put them in one of the normal trays, and run the trays through the xray.

My wife traveled out of Kansas City last weekend and was subject to this. She's a teacher, and traveled with grading, so they took out tests, her books, everything that was paper. The line agent said they were worried about papers being used to obfuscate other things in the xray machine. But that was the line agent, so he could have been (a) uninformed or (b) lying.

Trying to de-clutter the images by separating paper would fit the observed procedure too. It seems a little odd that it would start only now. Maybe screener testing recently showed better performance when paper is separated out.

Or perhaps there was some intel, or some cases where luggage was searched post scanner that came up with items that should have been caught. That might trigger a revision in procedures to prevent or reduce future cases, which is how I would expect and want a program that was actually meant to reduce danger to operate.

It may have involved some original research on the spectral properties of the material their looking for; in relation to the radiant energy they have available; and the spectral sensitivities of the sensors (radiant energy source spectra, object spectra, sensor spectra = information to derive a reflectance/absorption spectra for the object and match it with whatever you're looking for). But this research also requires any software changes and testing, and possibly changes to the light source (to change the wavelength(s) available), changes to filters on the light source or the sensor or both.

I think the limiting factor is the spectral response of this specific material, given a limited radiant energy source.

Another way to do this, would be via resolution. Maybe they aren't doing spectra matching, they might be able to differentiate the physical pattern of the material, sorta like a scanning microphotograph.

EDIT: One of the comments says, "They went through the Xray machine in a separate bin, much like your laptop does."

Stacks of paper may have densities similar enough to certain restricted liquids and polymers that distinguishing one from the other via x-ray is difficult.

i.e. plastic explosive sheets sharing space in a file folder, or bound with surrounding paper into what looks like a legitimate book.

They say it is a test program. Maybe they are not testing if it is effective but rather how much it slows down the screening?

It doesn't need to be nitrocellulose, you can impregnate ordinary paper with military high explosive using an appropriate solvent. But I doubt that is the purpose here because that could be handled by normal explosive detection mechanisms.

If this is the case (and I agree that it sounds likely) then what's the appropriate response from a bad guy? You don't take an action without considering a reaction...

Could this method be applied to fabric? Perhaps certain types of plastics? What if the bad guy hints that this is their plan with no actual intent other than misdirection. This could overwhelm screening resources, frustrating passengers, and stressing security agents while the actual threat could travel through another means, if it exists at all.

I traveled this weekend and can't help performing threat analysis against these security models. It's never made me feel better.

I flew out of MCI (American Airlines) on Sunday evening, confirmed this definitely happened. They asked for books, papers, notebooks, etc.

However, I disagree with one point in the article: I didn't witness them "scanning" the documents with a scanner. They went through the Xray machine in a separate bin, much like your laptop does. Perhaps I missed something.

Agreed. "Scanning paper" has spying implications. They are just xraying it in its own bin.

They seem to like dense things to be in their own bin. Books are pretty dense.

Maybe someone got caught with a lead-lined hollow book concealing a weapon?

Going a little off topic now...

I'm surprised nobody has combined 3D X-Ray Scanning with computer vision technology. At the moment we're depending on the human eye flicking between three dimensions and spotting bad things, with very basic shape detection to "hint" at objects of interest. This system kind of works, but has human error weaknesses.

If you fed 3D X-Rayed objects into a computer vision engine, eventually you'd have a big enough catalogue so the computer could list off every object inside and flag things which may be odd or problematic, for example a book with seemingly no internal dimensions.

Now this is an imperfect system, for example when a new form factor of laptop started getting sold it might flag it as unusual, but isn't that somewhat working as intended? Then they can scan it, clear it, and send back the scan as a reference image.

Eventually it could speed up and improve the reliability of bag checks.

That already exists, but are commonly used on baggage, not at checkpoints. I can't remember what airport I was at, but they were scanning bags in the terminal area before loading them on a belt.I saw a TSA employee stick a bag through the machine, and the machine found a bottle of wine wrapped and taped in bubblewrap and outlined the wine bottle with a red outline. The guy they set the bag off to the side (presumably for 'enhanced interrogation').

Envision, or invision was the brand name of the scanner?

They could also profile the contents, there's got to be a normal distribution of items in baggage for particular types of journeys?

I always presumed that they wanted the laptops in a separate bin because they were comparing them to a set of known images (of commercially sold laptops), but perhaps I'm giving them too much credit.

I doubt it. There are too many makes and models out there to make this a reasonable thing to do. I imagine that it is just to see things more clearly. A laptop is many layers of densely packed electronics. It would be very easy to hide explosives (in place of the battery, for example) and triggering mechanism in there.

"In place of"? It's trivial to cause a lithium-ion battery battery to explode if you know how. Don't tell TSA, though, or you're going to have a very boring flight.

Burn yes. Pop yes, but not the sort of explosion necessary to damage an aircraft. That guy on youtube making "grenades" from batteries ... they are more firecracker than weapon. You could do more damage with a bottle of vodka and a match.

True, but it's enough to make a rather spectacular show to frighten people, and in the end, that's what terrorism is about.

Anyone who's flown RC aircraft in the past decade knows all too well about this..

Spectacular light show, a good burn... yeah. Thats about it though... It wouldn't be worth a terrorists time... it would just be a light show and a smoke show, could start a fire, which would be bad, but honestly fires get suppressed pretty quick on modern airliners as long as they aren't started in the cargo area and ember for a while... in the end, any attack carried out with a LiPo/LiIon would just be an inconvenience...

The scenario that keeps some pilots up at night is unsecured human cargo in a panic. A medium fire won't ignite the plane but it will fill the cabin with fumes. Those drop-down oxygen masks are useless in such scenarios. Get enough people to panic, to run fore or aft, and one could create a crush event or even destabilize the aircraft.

From storeis though, panicked passengers in flight tend to stay calm... there is a sense of helplessness and acceptance that takes over pretty quick when you realize there isnt anything you can do

lol, no.

I recently flew with 20 lb of cheese. Definitely got re-scanned. Cheese is dense.

Nearly 40,000 calories dense.

But could you launch it 300m away from a trebuchet?

scanning as in screening. not scan to pdf.

Not yet, anyway...

On a flight a year or so ago, I had a TSA agent open up a book I had in my carryon to half a dozen different places to swab for explosives. Not sure if that's standard procedure though, I think I had annoyed him earlier.

> I disagree with one point in the article: I didn't witness them "scanning" the documents with a scanner. They went through the Xray machine in a separate bin

I think that's what was intended by the article:

Once the paper products were removed, the passenger had to put them in a separate bin to be scanned separately.

There seem to be a lot of people theorizing that it could be something about the paper itself that they're looking for, i.e. flash paper, paper circuits or physical one-time encryption pads, but what if it's not about the paper at all? Maybe, the TSA is simply trying to discourage passengers from traveling with or using paper, thereby encouraging people to store their information digitally on phones and laptops where that data can be more easily copied and analyzed?

Or it's simpler than that: security theatre. We're adding a new level of annoyance so people have this false impression their jobs aren't totally beyond worthless.

Fuck the TSA and the airlines. These days I'll pay more to take am AmTrak or just drive. Next time I fly, it will be after taking a train to Canada first. If I have to fly internationally, I'd rather not fly out of a US airport. I've flown through over a dozen countries, and yes, it is getting ridiculous everywhere, but America is still the worst. Especially when it comes to pat downs. No other country I've been through did pat downs except Moldova; and even theirs weren't anywhere near as bad (typically police arms/leg pat downs. No reaching under your belt or any other TSA bullshit for the false-positive/random-number-generator they try to tell you are body scanners).

> These days I'll pay more to take am AmTrak or just drive.

I take it you've never been searched by Amtrak police. Once on a cross-country trip all my belongings were searched twice - in Chicago where I departed, and again mid-trip.

It's not a great time.

It's not nearly so complex and conspiracy based...

They simply have found issue with dense objects (like books, stacks of paper) hinder the xray imaging they use in the scanners... thats all. Nothing special here...

Im sure over some bad-guy communication network it was mentioned to attempt to get contraband on a plane by masking its location in luggage under some seriously thick books or something...

Kansas City Airport doesn't use TSA screeners, they have a private contractor doing the screening:

https://www.tsa.gov/for-industry/screening-partnerships

That said, it seems like this policy is likely a TSA imposed pilot program:

https://thepointsguy.com/2017/05/paper-products-new-tsa-secu...

I don't believe this is true, how does one tell? They appear to be TSA agents, in the blue uniforms with the TSA badges

It's true. Turns out blue shirts can be worn by just about anybody.

Here's a story from last summer about the private security at Kansas City Airport: http://www.kansascity.com/news/local/article79795177.html

Good find!

Oh interesting. I am curious is the experience of the privatized screening any better?

Or is the amount of humiliation, infantilizing and browbeating of regular honest people about the same as the non-privatized TSA?

There was big uproar about privatizing the TSA about a year ago when the time spent in lines was growing even more excessive. That narrative about privatizing seemed to go dark. Is the Kansas City Airport itself a pilot program for privatization of the TSA?

Yes; I live in KC. The ones in MCI are polite, as opposed to Baltimore where they strut around barking orders.

Of course MCI had a distributed security and gates, so they are smaller and thus quieter.

Yeah I think the distributed security has a lot to do with customer satisfaction. The horseshoe design is really efficient for plane parking and the drop/pickup. Unfortunately, it's terrible for logistics like transfers :/

I think it's the best airport in the country. I can get from plane to car in 3 minutes. But yes, transferring airlines would be a pain, though flights on the same airline are usually within the same security zone.

Unfortunately the KC politicians keep scheming to build a new one. Fortunately the population wants to keep it.

Portland are TSA. SF is subcontracted. In my experience on the west coast, the real TSA blow the pants off the subcontracted ones. Portland is AAAAAaaamazing

SFO also doesn't have TSA screeners, and I believe the agents' uniforms actually don't have TSA badges. (Not sure about Kansas City, but I'd be surprised if any non-TSA agents had TSA badges...)

Is this a recent development?

Been the case for years. 2006, looking it up quickly.

Their uniforms say First Line.

Given that I've had this happen to me at a checkpoint (in Seattle) and had it explained to me, I think I have a reasonable potential answer: Stacked paper produces false positives in the scanning machines which can be flagged as suspicious substances. By separating the paper into a separate bin, it can be more quickly inspected by human eyes and the flag cleared, allowing the security line to be cleared more quickly.

Perhaps a bit cynical, but that is exactly the reason I would expect from the TSA.

It's not that they're enhancing their screening of anything in particular, they're just helping you get through more quickly... sureeeee.

I'm gonna go with TSA is looking for innovative new ways to inconvenience travellers.

Security theatre. Make people think they're being innovative when their jobs are truly worthless.

In the 90's I landed in the cockpit, I was 13. In 2017, US is on my no-fly list...

Any organizations' first imperative is to sustain itself. If security theatre is all they have, that's what we'll get and more of it.

If the TSA was shutdown entirely leading to terrorists blew up 10 planes a year in the US, flying would still be as safe as it was in the 1960s.

http://www.sfgate.com/nation/article/U-S-commercial-airlines...

For those w/o a working knowledge of 1960s air safety; are you saying removing the TSA would make us safer, less safe or simply that we tolerated the same level of safety w/o TSA 50ish years ago?

I'm not advocating removing the TSA entirely, just pointing out that we are paying a heavy price for a likely small benefit.

Locking the cabin door virtually eliminated the threat of turning jetliners into terrorist weapons at a tiny cost. But on top of that we've cost the country maybe a trillion dollars in excessive and invasive security procedures to prevent planes from being blown up. The TSA is only one part of those costs, longer travel times, reduced travel and lost liberties are a big part of it.

The value to terrorists blowing up an airliner is relatively small, there are far easier and cheaper ways to kill a few hundred people to make a political statement.

So my real question is, if we reduced spending on airport security, and reduced the level of security significantly so that we shaved 15 mins on average off every trip, would it be worth accepting a plane being blown up every few years?

Every year the US has nearly 1 billion trips by air. If you value travelers time at $20/hour, saving 15 minutes per trip directly saves nearly $5B a year. If the cost of saving those 15 minutes per trip is 50 lives per year, we are valuing each of those lives at $100m each. That seems incrediably excessive to me. Of course this is just a rough estimate, run your own numbers but it's hard to imagine the costs get down to a barely reasonable $10M per life level.

and remember that doesn't include the cost of the TSA or the cost of flights not taken.

The TSA doesn't just exist to stop terrorism. Also if the US didn't screen passengers, many other nations likely wouldn't accept flights originating from it.

How are you assessing the value of a human life?

I never advocated not screening passengers, just doing it more efficiently even if slightly less effective.

How are you assessing the value of a human life? I don't know of any study has ever gone above $10M.

With their current track record of 0 terrorists caught since 9/11, I think it would be much safer than the 1960s.

This ignores the deterrence factor

My theory: they aren't looking for paper, they are trying to rule it out as something else.

My understanding of these scanners is that they colour-code "organic" and "inorganic" material differently. Explosives generally show up as organic.

Now, if you have a block of such organic material in just the right position next to some electronics, the conveyor gets stopped and you will be taken to one side and asked some very direct questions about the contents of your bag.

I know this because I once had a protein bar in the same bag as a portable DVD player and that aisle went into lockdown for about 30 minutes because it looked exactly like a bomb, from all angles, in 3D. Expert called over, agreed they couldn't start the conveyor until they knew it was safe.

My guess is that paper (in the form of small pads) is the commonest cause of this type of false positive.

I can't wait till we have to travel in paper smocks, chained to our seats like the criminals we truly are.

I'm wondering if that would actually be any less humiliating than the current level of harassment by both the TSA and airlines themselves.

I wonder if being chained to our seats would reduce the risk of the airlines physically dragging us off of oversold flights?

What about those of us that can't afford first class!

No smock for you!

Eventually they'll just shoot you at the airport when you turn up, then throw your carcass into an incinerator, because aeroplane travel will have become so inconvenient that only the most devoted of terrorist would bother.

Each person is pushed into a tube from the top whilst the current resident is pushed out the bottom. Each tube is made of reinforced kevlar and whatever else you can imagine. Each person is naked and is allowed no carryons of any kind. This of course will also increase profits as you can fit more tubes than seats.

Okay, tin foil hat time.

Maybe they have new machines that can see the print through the paper, and actually scan and store the contents of all these papers in a timely fashion?

There was an MIT reasearcher a while ago (it may have been posted here) using THz wave radar to do this. I think it's the same band (ish) the body scanners use.

I kinda doubt those body scanners have anything remotely close to the spatial resolution required to find text written on a sheet of paper.

He said the same band. That wouldn't have anything to do with spatial resolution.

Sorry. I inferred that suggesting this meant (in the vein of this "tinfoil hat time" thread) that the body scanners might have the capability to read text from paper.

This is only tangential (I don't think the TSA is doing this), but this is similar to a fascinating technique for finding writing on discarded paper used as filler in bindings and such in old books.

https://medievalbooks.nl/2015/12/18/x-rays-expose-a-hidden-m...

Were you thinking of Terahertz time-gated spectral imaging for content extraction through layered structures[0]?

[0] https://www.nature.com/articles/ncomms12665

not impossible: http://news.mit.edu/2016/computational-imaging-method-reads-...

but probably not ready for use in airports yet, either.

Summary: Bruce doesn't know, and so he is asking his readers.

Yes, it would have been nice if the title explicitly stated that... i.e., "Does anyone know why the TSA is now scanning paper?"

That's Bruce's fault, OP just copy-pasted the title

A better summary is that Bruce is bring it to his readers attention because it's interesting.

I had my bag pulled out of the scanner while at SAN - was very frustrating as I was going between the 3-9 gates and the 1/2/2A gates on a connection - amazingly had to go back through security - and had only a few minutes before my connection left.

In an exasperated voice I asked the security person why she had to dig through my bag and she indicated that the paperback novel that I had in there was the trigger.

So I replied - guess I'm not going to take a paperback next time. Another freedom impinged.

Because blobs of paper look to similar to blobs of potential explosives when xrayed. They arent scanning it so much as removing it from the scan of everything else.

Do you know that to be true? Or is it that paper and/or ink blocks scanning and you can hide bombs in it?

It is the cellulose in the paper. Blocks of it are homogenous enough that they look similar in density to something dangerous. Add in ink, glue and other materials commonly soaked into paper and the situation is not totally unreasonable.

https://en.m.wikipedia.org/wiki/Nitrocellulose

I lack the expertise to comment on the sensitivity of the cellulose specifically, but the metro stations where I live will perform random stops as you enter, and the monitors are in plain sight. Notebooks, stacks of paper, and note cards are usually pretty clearly detected by whatever software they're using to help highlight items. It seems weird to me that there could be such difficulty with TSA scanners versus the small, older ones set up at stations here.

(St. Petersburg, Russia, just for reference for the location)

>Notebooks, stacks of paper, and note cards are usually pretty clearly detected by whatever software they're using to help highlight items

How do you know the problem isn't that the software flags dangerous items as paper incorrectly (which I think is the mostly likely problem here)? I doubt you've seen the X-ray image of someone smuggling nitrocellulose.

The software is just using density--if you have an explosive of similar density to paper, it's probably not going to flag it.

Well, I was more specifically replying to the comment "It is the cellulose in the paper. Blocks of it are homogenous enough that they look similar in density to something dangerous."

Every time I've seen it on the scanners here, or the glimpses I've seen at airports last I was in the US, usually it's very clear what you're looking at - books and other paper products are plain to see.

If they obfuscate, sure, possibly. But just from personal experience it doesn't seem like it would be indistinguishable.

I'm not saying that these tools are infallible by any means, just that the particular claim didn't mesh with my experience.

An x-ray only shows density. 2 equally dense objects will look the same regardless of chemical composition.

What you're likely seeing is computer enhanced images, which may be giving you a false sense of the capabilities of x-rays.

There are explosives with densities fairly similar to paper. A block of those explosives, and a block of paper would look very similar on an x-ray.

Blobs of explosive normally have a chemical composition that is different from blobs of paper in a way that a X-ray scanner would detect.

If somebody created an explosive that could pose as paper for X-ray, that would be noteworthy.

X-ray machines don't look at chemical composition, they care about density. Paper is quite dense, and a thick enough pile of it will show up as a solid block of 'something'.

They differ elements by row of the periodic table, and modern ones have special filters for separating a single interesting element from the rest of its row.

>Blobs of explosive normally have a chemical composition that is different from blobs of paper in a way that a X-ray scanner would detect.

How is that? If a block of explosives is close to the same density as a stack of paper, they're both going to show up as similar colored blocks on the X-ray.

X-ray differentiate atoms by electronic distribution.

Yup, my guess is that it was causing time-consuming false positives when jumbled together with everything else in the bag, so they set it aside. That way they're easier to verify as safe, since they're isolated and laid flat, and if a closer inspection is required they don't have to go through the whole bag. I'm guessing that's the same reason laptops are scanned separately as well.

I found this story by checking Google for updates in the news... sounds like the TSA has reversed course:

http://www.bizjournals.com/kansascity/news/2017/05/05/tsa-fo...

I think the point many people are missing is that this is a "new" development. All the talk about paper composition / features could overlap with other banned material cannot be new.

I found this, it may or may not be related. The gist is relatively recent research (2011) discussing using x-ray refraction rather than just attenuation and is capable of "creating precise images of the contours of all objects".

A New Generation of X-ray Baggage Scanners Based on a Different Physical Principle www.mdpi.com/1996-1944/4/10/1846/pdf

Maybe they're looking for flash paper.

https://en.wikipedia.org/wiki/Nitrocellulose

seems like regular nitrate sniffers would catch that, and x-rays would not

Seems like TSA does a lot of pilot programs that (luckily, imho) don't end up going anywhere. They once set up a folding table and searched everyone boarding my Greyhound bus.

They tried doing that at an Amtrak station a while ago and were forcibly removed from the premises by Amtrak police.

That's awesome. I remember hearing about their VIPR squads harassing people after they had disembarked a train at their destination. I'm glad Amtrak fought their bullshit.

I was curious, so I went looking. This article seems to describe what you are referring to:

http://www.cnn.com/2012/02/06/opinion/don-phillips-tsa-vipr-...

Does cash have a unique identifier that can be scanned for? If someone was trying to bring a wad of hundreds in a hole cut out in a book, maybe they'd be looking for that?

I think cash is already detectable.

I'm pretty sure it's perfectly legal to fly as much cash as you want domestically. [1] However, if they're scanning for other paper products that are potentially illegal, LSD comes to mind.

[1]: https://travel.stackexchange.com/questions/36740/is-there-a-...

Yep. Metallic ink is used in your green(/blue/red)backs. http://www.dailymail.co.uk/news/article-2120883/A-step-spywa...

I thought this might have something to do with printer steganography [1] but not if they are just X-raying the paper. Also I'm not sure whether that practice is ongoing--I haven't heard anything about it for years.

[1] https://en.wikipedia.org/wiki/Printer_steganography

This sounds more like the "department of imagined threats" justifying its existence, not actual security.

Even if there is ANY possible risk, what was their analysis? The odds of this are probably lower than being struck by lightning.

The only new things I want to hear out of the TSA each week are: which rules have now been REMOVED, and how many fewer minutes security lines are taking on average.

I've had agents ask me to take out a card game from my bag - apparently the thick stack of cards can look like C4 on the scanner.

Maybe some intelligence that people are inserting sheets of metal foil into stacks of paper to attenuate the x-rays and hide something underneath?

Assuming the airport X-ray machines aren't that powerful, I would guess that 15+ sheets of foil inserted into a book or similar might mask something underneath it fairly well?

but it would show up as masked or dark or low energy, then they can mark as "needs manual search". That does not require forcing "all" papers out of all bags.

I was assuming many thin sheets of foil, each separated by several pieces of paper might be more subtle, than say a slab of lead. Subtle masking vs completely hiding something else under it.

Maybe this?

https://en.m.wikipedia.org/wiki/Printer_steganography

A friend of mine was also queried about books in his bags before going through security. I was two steps ahead of him and was not.

This was in a comparatively small airport in Montana, so it's not an isolated trial, if it is a trial.

Wasn't there a scene in one of the recent Bond movies where a huge pile of cash had been treated in some kind of chemical that turned it into a bomb?

The World is Not Enough is the movie you're thinking of. From 1999, if you want to call that recent; going back 18 of the 55 years of Bond movies.

that's right. I was thinking it was one of the Daniel Craig films. In my defense I remembered the explosion was at MI6 and MI6 blows up twice under Daniel Craig's watch...

I was at MCI on Sunday and can verify this. Even with pre-check, I had to remove my engineering pad from my carry on pelican case.

Oh man, even with pre-check? So it completely defeats the point of pre-check then by making everyone take something out of their bag. Ugh.

I got a paper game (star realms) pulled out of my bag last Sunday. Interesting. Was about 120 playing card size pieced of paper.

Is there an opt-out for this? What if you just refuse -- can they deny you boarding, and is that legal?

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