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Security Analysis of TSA PreCheck

Interesting research: Mark G. Stewart and John Mueller, “Risk-based passenger screening: risk and economic assessment of TSA PreCheck increased security at reduced cost?”

Executive Summary: The Transportation Security Administration’s PreCheck program is risk-based screening that allows passengers assessed as low risk to be directed to expedited, or PreCheck, screening. We begin by modelling the overall system of aviation security by considering all layers of security designed to deter or disrupt a terrorist plot to down an airliner with a passenger-borne bomb. Our analysis suggests that these measures reduce the risk of such an attack by at least 98%. Assuming that the accuracy of Secure Flight may be less than 100% when identifying low and high risk passengers, we then assess the effect of enhanced and expedited (or regular and PreCheck) screening on deterrence and disruption rates. We also evaluate programs that randomly redirect passengers from the PreCheck to the regular lines (random exclusion) and ones that redirect some passengers from regular to PreCheck lines (managed inclusion). We find that, if 50% of passengers are cleared for PreCheck, the additional risk reduction (benefit) due to PreCheck is 0.021% for attacks by lone wolves, and 0.056% for ones by terrorist organisations. If 75% of passengers rather than 50% go through PreCheck, these numbers are 0.017% and 0.044%, still providing a benefit in risk reduction. Under most realistic combinations of parameter values PreCheck actually increases risk reduction, perhaps up to 1%, while under the worst assumptions, it lowers risk reduction only by some 0.1%. Extensive sensitivity analyses suggests that, overall, PreCheck is most likely to have an increase in overall benefit.

The report also finds that adding random exclusion and managed inclusion to the PreCheck program has little effect on the risk reducing capability of PreCheck one way or the other. For example, if 10% of non-PreCheck passengers are randomly sent to the PreCheck line, the program still is delivers a benefit in risk reduction, and provides an additional savings for TSA of $11 million per year by reducing screening costs—while at the same time improving security outcomes.

There are also other co-benefits, and these are very substantial. Reducing checkpoint queuing times improves in the passenger experience, which would lead to higher airline revenues, can exceed several billion dollars per year. TSA PreCheck thus seems likely to bring considerable efficiencies to the screening process and great benefits to passengers, airports, and airlines while actually enhancing security a bit.

Posted on June 28, 2016 at 2:10 PM • View Comments

Arresting People for Walking Away from Airport Security

A proposed law in Albany, NY, would make it a crime to walk away from airport screening.

Aside from wondering why county lawmakers are getting involved with what should be national policy, you have to ask: what are these people thinking?

They’re thinking in stories, of course. They have a movie plot in their heads, and they are imaging how this measure solves it.

The law is intended to cover what Apple described as a soft spot in the current system that allows passengers to walk away without boarding their flights if security staff flags them for additional scrutiny.

That could include would-be terrorists probing for weaknesses, Apple said, adding that his deputies currently have no legal grounds to question such a person.

Does anyone have any idea what stories these people have in their heads? What sorts of security weaknesses are exposed by walking up to airport security and then walking away?

Posted on May 31, 2016 at 6:35 AM • View Comments

Economist Detained for Doing Math on an Airplane

An economics professor was detained when he was spotted doing math on an airplane:

On Thursday evening, a 40-year-old man —with dark, curly hair, olive skin and an exotic foreign accent— boarded a plane. It was a regional jet making a short, uneventful hop from Philadelphia to nearby Syracuse.

Or so dozens of unsuspecting passengers thought.

The curly-haired man tried to keep to himself, intently if inscrutably scribbling on a notepad he’d brought aboard. His seatmate, a blond-haired, 30-something woman sporting flip-flops and a red tote bag, looked him over. He was wearing navy Diesel jeans and a red Lacoste sweater—a look he would later describe as “simple elegance”—but something about him didn’t seem right to her.

She decided to try out some small talk.

Is Syracuse home? She asked.

No, he replied curtly.

He similarly deflected further questions. He appeared laser-focused —perhaps too laser-focused —on the task at hand, those strange scribblings.

Rebuffed, the woman began reading her book. Or pretending to read, anyway. Shortly after boarding had finished, she flagged down a flight attendant and handed that crew-member a note of her own.

This story ended better than some. Economics professor Guido Menzio (yes, he’s Italian) was taken off the plane, questioned, cleared, and allowed to board with the rest of his passengers two hours later.

This is a result of our stupid “see something, say something” culture. As I repeatedly say: “If you ask amateurs to act as front-line security personnel, you shouldn’t be surprised when you get amateur security.”

On the other hand, “Algebra, of course, does have Arabic origins plus math is used to make bombs.” Plus, this fine joke from 2003:

At Heathrow Airport today, an individual, later discovered to be a school teacher, was arrested trying to board a flight while in possession of a compass, a protractor, and a graphical calculator.

Authorities believe she is a member of the notorious al-Gebra movement. She is being charged with carrying weapons of math instruction.

AP story. Slashdot thread.

Seriously, though, I worry that this kind of thing will happen to me. I’m older, and I’m not very Semitic looking, but I am curt to my seatmates and intently focused on what I am doing—which sometimes involves looking at web pages about, and writing about, security and terrorism. I’m sure I’m vaguely suspicious.

EDITED TO ADD: Last month a student was removed from an airplane for speaking Arabic.

Posted on May 9, 2016 at 1:15 PM • View Comments

Bringing Frozen Liquids through Airport Security

Gizmodo reports that UK airport security confiscates frozen liquids:

“He told me that it wasn’t allowed so I asked under what grounds, given it is not a liquid. When he said I couldn’t take it I asked if he knew that for sure or just assumed. He grabbed his supervisor and the supervisor told me that ‘the government does not classify that as a solid’. I decided to leave it at that point. I expect they’re probably wrong to take it from me. They’d probably not seen it before, didn’t know the rules, and being a bit of an eccentric request, decided to act on the side of caution. They didn’t spend the time to look it up.”

As it happens, I have a comparable recent experience. Last week, I tried to bring through a small cooler containing, among other things, a bag of ice. I expected to have to dump the ice at the security checkpoint and refill it inside the airport, but the TSA official looked at it and let it through. Turns out that frozen liquids are fine. I confirmed this with TSA officials at two other airports this week.

One of the TSA officials even told me that what he was officially told is that liquid explosives don’t freeze.

So there you go. The US policy is more sensible. And anyone landing in the UK from the US will have to go through security before any onward flight, so there’s no chance at flouting the UK rules that way.

And while we’re on the general subject, I am continually amazed by how lax the liquid rules are here in the US. Yesterday I went through airport security at SFO with an opened 5-ounce bottle of hot sauce in my carry-on. The screener flagged it; it was obvious on the x-ray. Another screener searched my bag, found it and looked at it, and then let me keep it.

And, in general, I never bother taking my liquids out of my suitcase anymore. I don’t have to when I am in the PreCheck lane, but no one seems to care in the regular lane either. It is different in the UK.

EDITED TO ADD (10/13): According to a 2009 TSA blog post, frozen ice (not semi-melted) is allowed.

Hannibal Burgess routine about the TSA liquids rules.

Posted on September 22, 2015 at 1:22 PM • View Comments

TSA Master Keys

Someone recently noticed a Washington Post story on the TSA that originally contained a detailed photograph of all the TSA master keys. It’s now blurred out of the Washington Post story, but the image is still floating around the Internet. The whole thing neatly illustrates one of the main problems with backdoors, whether in cryptographic systems or physical systems: they’re fragile.

Nicholas Weaver wrote:

TSA “Travel Sentry” luggage locks contain a disclosed backdoor which is similar in spirit to what Director Comey desires for encrypted phones. In theory, only the Transportation Security Agency or other screeners should be able to open a TSA lock using one of their master keys. All others, notably baggage handlers and hotel staff, should be unable to surreptitiously open these locks.

Unfortunately for everyone, a TSA agent and the Washington Post revealed the secret. All it takes to duplicate a physical key is a photograph, since it is the pattern of the teeth, not the key itself, that tells you how to open the lock. So by simply including a pretty picture of the complete spread of TSA keys in the Washington Post’s paean to the TSA, the Washington Post enabled anyone to make their own TSA keys.

So the TSA backdoor has failed: we must assume any adversary can open any TSA “lock”. If you want to at least know your luggage has been tampered with, forget the TSA lock and use a zip-tie or tamper-evident seal instead, or attach a real lock and force the TSA to use their bolt cutters.

It’s the third photo on this page, reproduced here. There’s also this set of photos. Get your copy now, in case they disappear.

Reddit thread. BoingBoing post. Engadget article.

EDITED TO ADD (9/10): Someone has published a set of CAD files so you can make your own master keys.

Posted on September 8, 2015 at 6:02 AM • View Comments

No-Fly List Uses Predictive Assessments

The US government has admitted that it uses predictive assessments to put people on the no-fly list:

In a little-noticed filing before an Oregon federal judge, the US Justice Department and the FBI conceded that stopping US and other citizens from travelling on airplanes is a matter of “predictive assessments about potential threats,” the government asserted in May.

“By its very nature, identifying individuals who ‘may be a threat to civil aviation or national security’ is a predictive judgment intended to prevent future acts of terrorism in an uncertain context,” Justice Department officials Benjamin C Mizer and Anthony J Coppolino told the court on 28 May.

“Judgments concerning such potential threats to aviation and national security call upon the unique prerogatives of the Executive in assessing such threats.”

It is believed to be the government’s most direct acknowledgement to date that people are not allowed to fly because of what the government believes they might do and not what they have already done.

When you have a secret process that can judge and penalize people without due process or oversight, this is the kind of thing that happens.

Posted on August 20, 2015 at 6:19 AM • View Comments

Reassessing Airport Security

News that the Transportation Security Administration missed a whopping 95% of guns and bombs in recent airport security “red team” tests was justifiably shocking. It’s clear that we’re not getting value for the $7 billion we’re paying the TSA annually.

But there’s another conclusion, inescapable and disturbing to many, but good news all around: we don’t need $7 billion worth of airport security. These results demonstrate that there isn’t much risk of airplane terrorism, and we should ratchet security down to pre-9/11 levels.

We don’t need perfect airport security. We just need security that’s good enough to dissuade someone from building a plot around evading it. If you’re caught with a gun or a bomb, the TSA will detain you and call the FBI. Under those circumstances, even a medium chance of getting caught is enough to dissuade a sane terrorist. A 95% failure rate is too high, but a 20% one isn’t.

For those of us who have been watching the TSA, the 95% number wasn’t that much of a surprise. The TSA has been failing these sorts of tests since its inception: failures in 2003, a 91% failure rate at Newark Liberty International in 2006, a 75% failure rate at Los Angeles International in 2007, more failures in 2008. And those are just the public test results; I’m sure there are many more similarly damning reports the TSA has kept secret out of embarrassment.

Previous TSA excuses were that the results were isolated to a single airport, or not realistic simulations of terrorist behavior. That almost certainly wasn’t true then, but the TSA can’t even argue that now. The current test was conducted at many airports, and the testers didn’t use super-stealthy ninja-like weapon-hiding skills.

This is consistent with what we know anecdotally: the TSA misses a lot of weapons. Pretty much everyone I know has inadvertently carried a knife through airport security, and some people have told me about guns they mistakenly carried on airplanes. The TSA publishes statistics about how many guns it detects; last year, it was 2,212. This doesn’t mean the TSA missed 44,000 guns last year; a weapon that is mistakenly left in a carry-on bag is going to be easier to detect than a weapon deliberately hidden in the same bag. But we now know that it’s not hard to deliberately sneak a weapon through.

So why is the failure rate so high? The report doesn’t say, and I hope the TSA is going to conduct a thorough investigation as to the causes. My guess is that it’s a combination of things. Security screening is an incredibly boring job, and almost all alerts are false alarms. It’s very hard for people to remain vigilant in this sort of situation, and sloppiness is inevitable.

There are also technology failures. We know that current screening technologies are terrible at detecting the plastic explosive PETN—that’s what the underwear bomber had—and that a disassembled weapon has an excellent chance of getting through airport security. We know that some items allowed through airport security make excellent weapons.

The TSA is failing to defend us against the threat of terrorism. The only reason they’ve been able to get away with the scam for so long is that there isn’t much of a threat of terrorism to defend against.

Even with all these actual and potential failures, there have been no successful terrorist attacks against airplanes since 9/11. If there were lots of terrorists just waiting for us to let our guard down to destroy American planes, we would have seen attacks—attempted or successful—after all these years of screening failures. No one has hijacked a plane with a knife or a gun since 9/11. Not a single plane has blown up due to terrorism.

Terrorists are much rarer than we think, and launching a terrorist plot is much more difficult than we think. I understand this conclusion is counterintuitive, and contrary to the fearmongering we hear every day from our political leaders. But it’s what the data shows.

This isn’t to say that we can do away with airport security altogether. We need some security to dissuade the stupid or impulsive, but any more is a waste of money. The very rare smart terrorists are going to be able to bypass whatever we implement or choose an easier target. The more common stupid terrorists are going to be stopped by whatever measures we implement.

Smart terrorists are very rare, and we’re going to have to deal with them in two ways. One, we need vigilant passengers—that’s what protected us from both the shoe and the underwear bombers. And two, we’re going to need good intelligence and investigation—that’s how we caught the liquid bombers in their London apartments.

The real problem with airport security is that it’s only effective if the terrorists target airplanes. I generally am opposed to security measures that require us to correctly guess the terrorists’ tactics and targets. If we detect solids, the terrorists will use liquids. If we defend airports, they bomb movie theaters. It’s a lousy game to play, because we can’t win.

We should demand better results out of the TSA, but we should also recognize that the actual risk doesn’t justify their $7 billion budget. I’d rather see that money spent on intelligence and investigation—security that doesn’t require us to guess the next terrorist tactic and target, and works regardless of what the terrorists are planning next.

This essay previously appeared on CNN.com.

Posted on June 11, 2015 at 6:10 AM • View Comments

TSA Not Detecting Weapons at Security Checkpoints

This isn’t good:

An internal investigation of the Transportation Security Administration revealed security failures at dozens of the nation’s busiest airports, where undercover investigators were able to smuggle mock explosives or banned weapons through checkpoints in 95 percent of trials, ABC News has learned.

The series of tests were conducted by Homeland Security Red Teams who pose as passengers, setting out to beat the system.

According to officials briefed on the results of a recent Homeland Security Inspector General’s report, TSA agents failed 67 out of 70 tests, with Red Team members repeatedly able to get potential weapons through checkpoints.

The Acting Director of the TSA has been reassigned:

Homeland Security Secretary Jeh Johnson said in a statement Monday that Melvin Carraway would be moved to the Office of State and Local Law Enforcement at DHS headquarters “effective immediately.”

This is bad. I have often made the point that airport security doesn’t have to be 100% effective in detecting guns and bombs. Here I am in 2008:

If you’re caught at airport security with a bomb or a gun, the screeners aren’t just going to take it away from you. They’re going to call the police, and you’re going to be stuck for a few hours answering a lot of awkward questions. You may be arrested, and you’ll almost certainly miss your flight. At best, you’re going to have a very unpleasant day.

This is why articles about how screeners don’t catch every—or even a majority—of guns and bombs that go through the checkpoints don’t bother me. The screeners don’t have to be perfect; they just have to be good enough. No terrorist is going to base his plot on getting a gun through airport security if there’s a decent chance of getting caught, because the consequences of getting caught are too great.

A 95% failure rate is bad, because you can build a plot around sneaking something past the TSA.

I don’t know the details, or what failed. Was it the procedures or training? Was it the technology? Was it the PreCheck program? I hope we’ll learn details, and this won’t be swallowed in the great maw of government secrecy.

EDITED TO ADD: Quip:

David Burge @iowahawkblog

At $8 billion per year, the TSA is the most expensive theatrical production in history.

Posted on June 2, 2015 at 7:37 AM • View Comments

Hacker Detained by FBI after Tweeting about Airplane Software Vulnerabilities

This is troubling:

Chris Roberts was detained by FBI agents on Wednesday as he was deplaning his United flight, which had just flown from Denver to Syracuse, New York. While on board the flight, he tweeted a joke about taking control of the plane’s engine-indicating and crew-alerting system, which provides flight crews with information in real-time about an aircraft’s functions, including temperatures of various equipment, fuel flow and quantity, and oil pressure. In the tweet, Roberts jested: “Find myself on a 737/800, lets see Box-IFE-ICE-SATCOM, ? Shall we start playing with EICAS messages? ‘PASS OXYGEN ON’ Anyone ? :)” FBI agents questioned Roberts for four hours and confiscated his iPad, MacBook Pro, and storage devices.

Yes, the real issue here is the chilling effects on security research. Security researchers who point out security flaws is a good thing, and should be encouraged.

But to me, the fascinating part of this story is that a computer was monitoring the Twitter feed and understood the obscure references, alerted a person who figured out who wrote them, researched what flight he was on, and sent an FBI team to the Syracuse airport within a couple of hours. There’s some serious surveillance going on.

Now, it is possible that Roberts was being specifically monitored. He is already known as a security researcher who is working on avionics hacking. But still…

Slashdot thread. Hacker News thread.

EDITED TO ADD (4/22): Another article, this one about the debate over disclosing security vulnerabilities.

Posted on April 21, 2015 at 5:26 AM • View Comments