Matt Blaze: How unpredictable screening helps terrorists

http://www.crypto.com/blog/random/

by alterego • 17 years ago

56 62 17 years ago

crypto.com

wendroid• 17 years ago

4 in 5 people scanned, send 5 people

chaosmachine3• 17 years ago

Those still aren't very good odds.

tptacek12• 17 years ago

You can't talk about odds without talking about returns. 1-in-5 is f'ing fantastic if a $1 bet pays $1000.

bensummers• 17 years ago

Defenders must prevent every possible attack.

Attackers must evade the defenses just once.

elblanco• 17 years ago

It's like the old Star Trek joke:

Kirk: Mr. Spock, how many ways are there to die on this planet?

Spock: 3 Captain

Kirk: Very good, let's bring 3 guys in red shirts down to the planet with us.

CWuestefeld• 17 years ago

Relevant parts:

Paradoxically, the best terrorist strategy (as long as they have enough volunteers) under unpredictable screening may be to prepare a cadre of suicide bombers for the least rigorous screening to which they might be subjected, and not, as the strategy assumes, for the most rigorous. Sent on their way, each will either succeed at destroying a plane or be caught, but either outcome serves the terrorists' objective. ...

We might reflexively assume that any passenger screening system needs to be 100% effective at detecting all possible weapons and dangerous objects, an obviously difficult task. But, fortunately, that's not the requirement. Instead, the mechanisms need only be highly effective at detecting objects that can create actual terror under the conditions they will be subjected to in an actual flight. That is, in order to have meaningful security screening, we first must understand what it realistically takes to bring down an airplane. The security system can then be designed specifically to eliminate the preconditions for successful terrorism.

The TSA's much maligned "three ounce" liquid rule is, in fact, a nice example of good security engineering of this kind. ...

tptacek12• 17 years ago

The idea that Matt Blaze thinks the three-ounce rule is sensible was surprising to me; I hit it, jumped back to the top, and re-read the whole article. What's the flaw in his reasoning? The three-ounce rule always seemed like one of the more ridiculous TSA measures.

rogersm3• 17 years ago

After all, the latest bomber was carrying 80 grams, less than three ounces.

jz• 17 years ago

I was also surprised by this. The three-ounce rule applies to a single passenger. All it takes is a bit of team work to get around it. A 747 for example can carry between 400 and 500 passengers depending on class layout. A team of 3 terrorists would represent less than 1% of the passengers.

almost• 17 years ago

If you think about it there are things you can do with a not too large an amount of liquid chemicals that would cause serious problems on plane. I don't think making explosives is one of them.

NikkiA• 17 years ago

His reasoning appears to be 'no-one has blown a plane up with liquid explosives, therefore it must be working', at least that was the impression I got from the article.

ghshephard10• 17 years ago

What is the alternatives to preventing liquid bombs from bringing down an Airplane? What Matt Blaze is saying, is that instead of eliminating _all_ liquids (which would have also prevented aircraft from catastrophic explosions) - the TSA simply did the engineering to determine what the smallest amount of liquid was required to do significant damage, and then limited bottled liquids to something smaller than that. People can still bring on toothpaste, shampoo, and other useful liquids/medicines, but at the same time can't bring them on in large enough volumes to destroy an airplane.

itistoday• 17 years ago

It's perfectly possible that an organization headed by the government whose primary focus is the security of airline passengers is completely incompetent and ineffective.

But is it not also possible that the TSA is purposefully putting on the guise of an incompetent governmental entity? That would seem like an excellent strategy to take, as it follows the principles in Sun Tzu's Art of War to the letter. If you are strong, appear weak, if you are weak, appear strong, etc.

If these terrorists think they can easily game the system, it will likely lead them to be less cautious, exactly as stated in the article:

That seems like a good thing to me, and if this is the TSA's actual strategy, it's a smart one. Say one thing publicly, but do another privately.

thesethings• 17 years ago

Whoa. You must blew my mind. I really want this to be true :D

pvg• 17 years ago

But is it not also possible that the TSA is purposefully putting on the guise of an incompetent governmental entity?

It's extremely unlikely. For one thing, appearing incompetent in order to encourage the incautious, freelancers, amateurs and copycats is essentially using the public as bait - if you happen to miss one, people die. As a strategy it's morally and probably legally questionable.

kscaldef• 17 years ago

Personally, my take on the "unpredictable security measures" is that what's really being said is "things are pretty chaotic here and we don't really have a well-though-out plan in place, but we're going to try to cover that up by claiming that the inconsistency is actually intentional".

tptacek12• 17 years ago

This article demonstrates what I like about Matt Blaze's physical security writing that I don't like about Schneier's.

Both are computer security experts by training, but Blaze's writing has a concrete engineering-driven perspective that Schneier's lacks. Schneier's writing always "feels" right, but leaves you with the sense that's it's not based on any operational reality.

It's probably not a coincidence that Matt Blaze has done formal research on physical security topics (safecracking, wiretapping, etc) --- in addition to being a bona fide computer scientist.

rogersm3• 17 years ago

First of all I must say I don't believe in these kind of unpredictable systems: rarely doing this 'select randomly the process from a set of processes' works better than using the best process in the set.

But I don't think this applies:

  But terrorist organizations -- especially those employing 
  suicide bombers -- have very different goals and incentives 
  from those of smugglers, fare beaters and tax cheats. 
  Groups like Al Qaeda aim to cause widespread disruption and 
  terror by whatever means they can, even at great cost to 
  individual members. In particular, they are willing and 
  able to sacrifice -- martyr -- the very lives of their 
  solders in the service of that goal. The fate of any 
  individual terrorist is irrelevant as long as the loss 
  contributes to terror and disruption.

Training a terrorist has a cost, and he should succeed the "fate of any individual terrorist is not irrelevant". The terrorist group does not have an infinite number of terrorists (as he correctly concedes in the next paragraph).

So random screening works, not because that influences the behavior even of those who aren't checked, but because makes executing the attack more expensive to overcome the possibility of being detained in the random test.

Of course random screening is not as good as full screening, but from a realistic point of view is the only thing you can apply without shutting down world economy.

alterego2• 17 years ago

But if you read the article, I believe the point was that if the terrorist gets caught under a random system, the terrorist still achieves a positive result for the terrorists (the govt becomes forced to shut down aviation and then apply the maximum screening to everyone, causing expensive chaos and terror of its own).

gojomo3• 17 years ago

Also, consider that the greatest threat is not from people who hope to live and accept a strategic risk of death. Rather, the greatest threat is from people who believe that death is the ultimate success, for both their worldly and otherworldly aims.

While a one-in-a-twenty chance of success sounds good from a terror chief's perspective, no suicide bomber wants a 95% chance of winding up in captivity, famous only as a failure. Out of the twenty, they want to be the one!

So plans that allocate many participants to expected capture will have far fewer volunteers. And every report of a capture will decrease potential-volunteers' willingness to sign up, because they will adjust upward their expectation of embarrassing capture rather than martyrdom.

tptacek12• 17 years ago

Ramping up a new KSM has a high cost. Ramping up a mujahedeen to skirmish with NATO in Khost has a high cost. Ramping up the guys who know how to rig PETN bombs has high cost. Ramping up guys who can operate safe houses and route money through a paranoid cell system has a high cost.

Building the system has a high cost. Using the system to exploit the dumbfucks who get captured by the system in order to get them to put the explosive underpants on is cheap.

If the system was jeopardized by any terrorist attempt, you'd be right. But it isn't. It's like spam. It may have a 0.001% conversion rate, but as long as it pays off 10000000:1, it's sustainable and resilient.

ghshephard10• 17 years ago

Another thing to note - Matt Blaze typically approaches security scenarios with a different cost/benefit perspective than Schneier, for example Blaze writes:

"The TSA's much maligned "three ounce" liquid rule is, in fact, a nice example of good security engineering of this kind. "

Schneier, on the other hand, considers the inconvenience to travelers to be not worth the hassle. He always seems to fail to recognize the principles of defense-in-depth, and over-emphasizes the importance of stopping the terrorist before they launch an attack. I say this as someone who has ready pretty much every essay and book he has ever written, sometimes multiple times.

For example:

http://www.schneier.com/blog/archives/2006/08/terrorism_secu...

". Banning box cutters since 9/11, or taking off our shoes since Richard Reid, has not made us any safer. And a long-term prohibition against liquid carry-ons won't make us safer, either. It's not just that there are ways around the rules, it's that focusing on tactics is a losing proposition."

o Banning box-cutters (and other sharp devices) has made it much more difficult to bring on an _effective_ weapon on board a plane. Nobody is denying that you can still fashion a shiv, of some kind - but the amount of damage you can do with a roughly fashioned hand weapon, versus something designed to kill lots of people at close range, is enough to deter people from trying to do so. Note - one of the principal reasons for banning box cutters and their like is so that the _other_ passengers on the plane have a pretty straightforward mechanism for subduing a malevolent passenger.

o Banning Large amounts of liquids, in the face of Liquid Bombs being _actually designed_ just makes good sense. Likewise banning powdered substances (PETN) from being brought onto planes makes sense now that we know that there are active attempts to use this vector.

Focusing on tactics is actually a very effective proposition - It's actually pretty damn difficult to bring down a plane these days from inside - not impossible, I'm sure there are a lot of vectors still left, but they are getting pretty few and far between. Not to say you don't still try and stop attacks at their source, but, if one gets by - you hope that further lines of defense will stop them.

tptacek12• 17 years ago

Maybe it's just that Blaze's stuff seems falsifiable, and Schneier's stuff is slippery and abstract. At least we can argue rationally about the three-ounce rule. But if you accept Schneier's argument, there's no incremental discussion to be had.

Even if I agree with that (I do more than I don't), it's not productive. Regardless of whether "it's time for the TSA to go" (+34 yesterday last time I checked), the TSA isn't going anywhere. Shut up?

jeremyw• 17 years ago

He always seems to fail to recognize the principles of defense-in-depth...

That's a broad claim given that Schneier's built his reputation/business around defense-in-depth. It's practically his hobby horse and I don't read any such misunderstanding in his essays on the TSA.

sethg• 17 years ago

the best terrorist strategy (as long as they have enough volunteers)

Do they have enough volunteers? The Shoe Bomber and the Undie Bomber, compared with the team that pulled off 9/11, are a couple of amateurish mooks. If these are the best men that al-Qaeda can send against the United States, they must not have a very deep bench.

mattm• 17 years ago

If you recall, at least one of the 9/11 hijackers almost missed his flight because he was late. Al-Qaeda is not sending its best men for these missions. Why would an organization send its best men if they are going to end up dead or in jail?

It doesn't make sense. You send the worst people possible that have a chance of pulling it off.

CamperBob• 17 years ago

That's just it... the people who pulled off 9/11 were a bunch of amateurish mooks. A bunch of amateurish mooks with an 18 in the Luck department is still dangerous.

Just as in this case, there were any number of measures already in place that could have stopped 9/11, if they had only been followed. More rules are not the answer.

dandelany• 17 years ago

Well, sort of. They were 19 amateurish mooks who had gone to flight school. That's a far cry from a couple of idiots with unsuccessful bombs.

pedrocr2• 17 years ago

The problem is that with non-random screening the terrorists can be much more efficient. They can get a pool of candidates together and send them on flights without any explosives on them. They can then find out which of the guys get screened at a rate less than chance and send those on the actual attack. That's why random screening is the best system possible because any other system would have to be perfect, otherwise any flaw can be detected on dry runs and exploited for the attack.

This was thoroughly explored last time the TSA tried to be smart about screening and implemented its Computer-Assisted Passenger Screening System. MIT article exploring it:

http://groups.csail.mit.edu/mac/classes/6.805/student-papers...

alterego2• 17 years ago

I think this article isn't talking about random vs. profiled (which is what the mit paper is about), but random vs. 100% (where there 100% has been analyzed carefully to be sufficient to detect large bombs, etc.).

pedrocr2• 17 years ago

He was hand-waving at the end about the 100% but that's not a solution. They are doing it randomly because 100% is simply not possible. My point was that in a situation where 100% is not possible, as in real life, any system is potentially worse than randomness.

Maybe this just means we need to come up with screening mechanisms that can be applied to 100%, but given the current capabilities, choosing random screening is better than profiling.

zmimon• 17 years ago

It seems to me that the right approach should always have a significant random element, not as a deterrent, but as a check on how well the non-random component is working. The random part will examine in depth to find anything that should have been found in the non-random part but wasn't (say, body searches to find large metal objects making it through the x-ray screen at the airport). Without that you would be blind to defects in the system.

bdr• 17 years ago

The problem with this post is his answer to the question "What do we do when we detect a terrorist through random screening?" His answer is "shut down all commercial aviation until the the most rigorous screening possible can henceforth be applied universally, effectively creating the same kind of havoc that occurs after a successful attack", and his whole post rests on this point, but I think it's totally flawed.

- Shutting down commercial flight is better outcome (for the defender) than the the destruction of 9/11 - There are alternative responses, such as heightened screening, tighter in-flight security, or checking passenger lists for people with known connections to the terrorist caught.

neilk2• 17 years ago

The article hinges on the proposition that a failed attack still serves the terrorist network's purposes. Seriously, can you imagine a terrorist being briefed like this?

"Well, if you succeed, you may shock the world and rally the Muslim nations to our cause, while drawing the Great Satan into an unwinnable war costing over a trillion dollars. If you fail... well, you're going to cause a lot of air travellers to be a little annoyed for five minutes."

There is this idea that terrorists are like devils, delighting in causing misfortune of any kind. I don't think that's the case. Al-Qaeda has concrete goals, like advancing Wahabbi ideology or ejecting the USA from the holy places. Failed missions don't support that, do they?

pyre3• 17 years ago

Do you really think that they would tell the suicide bomber that he/she might fail?

neilk2• 17 years ago

It was just to demonstrate a certain absurdity. No, that conversation might not happen, but the point was that the terrorist planners have objectives beyond "cause mayhem". And that increasing airline security costs probably don't even rank on their scale of worthy goals.

In Afghanistan, al-Qaeda is bleeding the USA of billions of dollars every month. But the article suggests that merely inconveniencing air travellers -- to the tune of maybe a few hundred million a year, widely dispersed -- might rank as an acceptable second best to a terrorist.

johnl• 17 years ago

Random usually ends up being discrimination so I would go with a set of more stable rules that apply to everyone.

Matt Blaze: How unpredictable screening helps terrorists

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