Ethan Zuckerman’s online home, since 2003

TSA Pre-Check, Fairness and Opaque Algorithms

Running late for a flight from Boston to San Francisco today, I was delighted to discover that my boarding pass made me eligible for the “TSA Pre-√” line. Instead of waiting in a labyrinthine line, removing my bottles of shampoo, my shoes and my laptop, I found myself as the only person waiting to use the metal detector, with TSA agents assuring me that I could simply take my phone out of my pocket, leave my bags on the conveyer belt and step through. It took less than 30 seconds to clear security. It felt great. And it felt like cheating.

I fly about 100,000 miles a year, mostly with Delta, so I’m just shy of Delta’s highest tier of frequent fliers. Some months ago, Delta offered me the option of sharing my frequent flier status with the TSA, in order to expedite security checks. Unlike programs like Clear, which requires a substantial annual fee, a special ID card and biometric scans of flyer’s retinas, opting into this program was free and involved selecting a checkbox. I opted in, and promptly forgot about it, until checking into a flight at Detroit a few months ago, I found myself invited into the Pre-√ line and whisked through security. It was surprising, weird and pleasant – I thought about tweeting about how pleasant the experience was, until I realized that I was also pretty uncomfortable with a system that seemed to provide such unequal treatment for frequent flyers and occasional travelers.

The logic behind Pre-√ is pretty straightforward. I’ve flown a lot in the past two decades, and haven’t threatened the safety of passenger, plane or crew – if we project future behavior based on past behavior, I look pretty unlikely to smuggle dangerous items onto a plane. TSA has limited resources to passengers, so they should focus on the unfamiliar, who are less predictable and more threatening. And since frequent travelers experience the most frustration with TSA delays, changing their experience with security procedures is likely to have the most impact on perceptions of the TSA and their function.

But there are some unexpected consequences in making security more pleasant for frequent travelers. Bruce Schneier’s observation that most airport security measures represent “security theatre” rather than actual security enhancements – like reinforced cockpit doors – comes into very sharp relief when your shampoo no longer needs special scrutiny, and your shoes are assumed to be explosive-free. It’s harder to tolerate the petty rules that govern flight security – “Sir, I’m throwing out your toothpaste because the tube once held 125ml, and though it’s obvious it’s almost entirely empty, the rules say that anything over 100ml can’t fly, so good luck brushing your teeth tonight” – when it’s made abundantly clear that they’re completely arbitrary, largely disconnected from actual security threats and enforced as public performance. There’s an odd cognitive dissonance in having the TSA abandon security theatre so totally – while I know the rules that have just been waived are arbitrary and ineffective, I find myself experiencing brief anxiety at realizing that the rules have been relaxed for me and others who fit some unknown sort of profile. (More on that in a moment.)

There are a variety of reasons to be discomfited by Pre-√. Consumer advocate Ralph Nader notes that splitting the security experience into a smooth one for frequent travelers and a harsh one for infrequent fliers suggests that we’re unlikely to loosen travel restrictions across the board. Frequent fliers are the people most likely to complain about TSA procedures and push for reform, and if they’re accommodated separately, political pressure to reduce security theatre is lessened. “The only thing that has developed tolerance for this mass nonsense that is going on at the T.S.A. checkpoints is that everybody is supposed to be exposed to it…. Once that is shattered there is going to be a lot of resentment among those who watch others zip through while we wait and nudge forward and get shouted at to take our shoes off.”

He’s right, which is probably why the two Pre-√ lines I’ve been through are physically separated from the normal TSA screening area – I know I’m getting the light treatment, but the infrequent travelers don’t, and the security theatre is for them, after all. So long as I’m treated well, I have no incentive to lobby for change, and if the infrequent fliers can’t see my experience, they won’t know how arbitrary and unnecessary the procedures they’re going through are. Long security lines could be a source of solidarity, but we lose that possibility when frequent travelers get special privileges. Writing in Salon, Michael Lind takes this argument to an extreme, suggesting that frequent fliers clubs are a way of privileging the rich and reflect the deep inequalities of our society. “Why don’t we just make the new class-based discrimination official? Instead of leaving it to airlines and other corporations to construct the new apartheid piecemeal and informally, let the government issue a Premium Elite Citizen Card, valid for multiple purposes.” I’m far from convinced that treating your most frequent customers well by letting them board an airplane first constitutes apartheid, but I’d agree that blurring a line between a status offered by an airline for frequent passengers to a status that gives you a different experience with a government agency, the TSA, is complicated and uncomfortable.

The conversation about Pre-√ is more than a little different in frequent fliers forums. Fliers keep score of how often they’re waved into the Pre-√ line and how often they have to suffer ordinary security experiences. And they get annoyed at the unpredictability of the system, noting that if they knew they’d be granted Pre-√ every time they flew, they could arrive at the airport later. One flyer calls the program “amazing and useless at the same time“, because he can’t count on a quick screening experience.

This randomness is unlikely to disappear from the program, as it’s a major security feature. The TSA has published some of the criteria it uses to determine who’s eligible for pre-screening: frequent travelers who’ve opted in, who don’t have weapons or explosive violations on their criminal records. This suggests that would-be terrorists could start looking for frequent fliers with clean criminal records and recruit them as suicide bombers. One of the protections against that vulnerability is to ensure that Pre-√ flyers experience more intense scrutiny on some flights so that there’s no guarantee that a cleared traveler is a surefire path through less intense screening.

Because the screening is, in part, random, it’s going to raise questions about fairness. How do we know the TSA isn’t engaging in racial profiling, prohibiting travelers with Arab heritage from participating in Pre-√? Friends who’ve been closely involved with Wikileaks report that they are now selected for secondary screening virtually all times they travel, making clear that profiles, based at least in part on behaviors or political views, can affect your TSA experience. It’s reasonable to expect that, if Pre-√ continues, frequent travelers will complain that they’re systematically being left out, punished for some part of their profile they can’t review or challenge.

Here, the TSA faces a challenge that surfaces in a wide range of settings: the difficulty of publishing algorithms. A truly fair Pre-√ system would involve publishing the algorithm the TSA uses to determine who’s safe to fly, and allowing travelers to review whether they qualified and why. But publishing that algorithm increases the chances that it will be gamed – if we discover that flying 20 times in a year is a key factor for clearance into the program, it’s easy to imagine an adversary flying 20 times with clean hand baggage and a bomb smuggled on the 21st flight.

Google faces a similar problem with their search algorithm. Countless merchants have complained that Google ranks their sites too low in search results, sending business to their competitors. The more paranoid (or, perhaps, more savvy?) suspect that Google is running an extortion racket, offering high “organic” placement to those who purchase ads, punishing those who don’t. Google could address this fear by publishing their algorithm and allowing sites to see how they ranked on different components of the algorithm. They don’t, because this would be hugely useful to the many people who’d benefit from gaming the system. (The entire SEO industry is based around the premise that search algorithms can be gamed with sufficient knowledge – actually providing that information would be of massive benefit to SEO firms and their clients, and likely to very little user benefit.)

It’s possible to make an algorithm transparent and gaming resistant – it’s just very hard. You need to engineer algorithms where signals are expensive to fake. The purest form of Google – the “BackRub” algorithm – is vulnerable to gaming because the signal (the number of pages linking to a page) is inexpensive to fake – create a “linkfarm” of pages pointing to your page, and you’re all set. Google’s algorithm may need to be obscure because in an online environment, virtually all signals can be faked, given enough skill and effort.

TSA Pre-√ could well be another matter. If the main signal the program uses is lots and lots of trips without incident, that’s a reasonably expensive signal. Our aspiring terrorist might need to take hundreds of trips, spending tens of thousands of dollars, before establishing a sufficiently clear reputation. Or she might have a great advantage, now knowing precisely what type of frequent flier she needs to recruit to smuggle on the all-important 125 ml of scary liquid. I certainly don’t count on TSA making the algorithms behind Pre-√ transparent, but it would be a small step towards addressing questions of fairness the program is likely to face.

We’ve seen a strong push for open data in the US, a movement based on the idea that data should be available to the general public in machine-readable, API-addressable form, unless there’s very strong reasons to keep it secret. I’d like to see a similar push around transparent algorithms, a principle that our government should be disclosing algorithms that affect the lives of citizens, in as many circumstances as possible. I suspect we’d learn a great deal about making algorithms transparent and gaming-resistant if it were significantly harder to rely on security via obscurity.

11 Responses to “TSA Pre-Check, Fairness and Opaque Algorithms”

  1. Bill Fisher says:

    PreCheck is PR garbage by TSA not improved airport security.

    In the past 18 months 2 million people have used Pre Check, some of them several times. There are over 700 million passengers each year or 1.05 billion people in that time.

    Providing an exemption based on frequent flier status on a private sector airline has to be illegal. This is no different than allowing people who buy a Volt or belong to AAA to ignore the speed limit. The concept is identical.

    The chances of you being able to use this is 0.19% or less than 2 in 1,000 trips and then only if you are a Delta, United, American or US Airways frequent flier. If you fly on Southwest or Jet Blue forget it.

    If they increase this to 100 times its current size, that would still be less than 200 in 100,000 or 1 in every 500 passengers. That is not going to speed up the lines for anyone but the privileged.

    Why would the average person be happy about biased program that favors the frequent fliers and treats them as being more equal than everyone else? We all pay the same amount for TSA, No one should get special treatment from TSA because they spend a lot of money with United Airlines.

    TSA is extending this to 2.2 million Federal workers with SSI clearance next year. Most will be exempt from TSA screening. Nice perk for Fed workers who make these rules.

    Would people be happy if TSA offered this only to millionaires, whites, men or college graduates? If not then they should oppose this along with the exemptions for other ‘special” groups.

    If these security measures aren’t applied to everyone equally, then they simply won’t work and should be stopped.

  2. Dan Murray says:

    Try going to the airport at least two times a week for the last 100 weeks and the Pre Screen doesn’t seem so unfair. If you travel once every year the cumulative time you spend in line is a fraction of what frequent travelers do in a year. I’m sorry…I don’t feel guilty.

  3. Bill in San Francisco says:

    Dan Murray, Pre Screen is just as unfair whether you’re a frequent traveler or not, and so is the “First Class Travelers Get The Short Line” deal some airports seem to have. It’s the TSA’s way of extorting a bribe (paid either in cash, information, or both, depending on which program it is.) If you travel enough, or belong to a terrorist organization, it’s worth paying the bribe, but it’s still unfair to everybody.

  4. bakum says:

    @bill why does fairness matter? TSA is supposed to prevent terrorists with as luttle inconvenience as possible. you could argue pre-check isn’t effective on either count, but fair? who cares?

  5. Bill says:

    Sorry folks, just because you are qualified for Pre-Check doesn’t even mean you get in. I’ve only made it through once since my city(ATL)started it. The other 10+ times I’ve had to go the normal route.

  6. Mo says:

    Anyone can sign up for Pre-Check without being a frequent flier. Anyone who signs up for the CBP Global Entry Program is automatically entered into Pre-Check. The cost for Global Entry is $100 for 5 years.

  7. Ken Nemeth says:

    Three thoughts:

    1. This is no different from any other frequent flyer perk. When I fly a lot over the year or fly first class, at almost every large airport around the world, I get to go to the front of the line. Internationally in some places if you pay enough money you’re escorted from the first class lounge directly to the gate and on the plane.
    2. Truly affluent people avoide commercial airports altogether and take private jets without having to go through any of this.
    3. This situation has been with us since the beginning of time. Tiered experiences based on wealth and influence. Why is everyone so upset about this particular iteration of it?

  8. Grady says:

    TSA is a government agency, paid for by taxes. Airports are, by and large, public services paid for by taxes. That means passengers should be treated equally, regardless of how often they fly.

    When airlines build and pay for their own airports and the security thereof, then they can treat different classes of passengers differently. But public money needs to treat us all the same.

  9. J.R. Ewing says:

    Something else I’ve also noticed – regrettably – since I was accepted is that not only is Pre- a system designed to buy off FF’s, it’s also a tool for TSA to threaten them with, too.

    I went through a Pre- line in Houston a couple of weeks ago and got into a disagreement with the clerk running the x-ray machine. He and all of the other clerks at the checkpoint couldn’t stop telling me – repeatedly – that Pre- is a “privilege” and if I made too much trouble, I’d lose my privileges.

    Basically, it’s a system something like the upper class in an old communist country: once you’re in the privileged class, you had better go along with the program or else, and if you don’t keep your head down we’ll will bust you back to being one of the “ordinary people.” Now, do you really want to complain that I’m unnecessarily spending too much time x-raying your bag? Do you?

  10. CBGB says:

    TSA is paid by user fees not by tax dollars.

  11. I was so happy that my Boarding Pass showed TSE Pre lately. Saved a tone of time at busy HNL airport. The government has my fingerprint already – but that’s another story…

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