The September 11 terrorist attacks and their aftermath
Bruce Schneier
{Request for wide distribution of CRYPTO-GRAM SPECIAL ISSUE, September 30, 2001}

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              September 30, 2001

              by Bruce Schneier
               Founder and CTO
      Counterpane Internet Security, Inc.

A free monthly newsletter providing summaries, analyses, insights, and commentaries on computer and network security.

Back issues are available at <>.  To subscribe, visit
<> or send a blank message to

Copyright (c) 2001 by Counterpane Internet Security, Inc.

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This is a special issue of Crypto-Gram, devoted to the September 11 terrorist attacks and their aftermath.

Please distribute this issue widely.

In this issue:
     The Attacks
     Airline Security Regulations
     Biometrics in Airports
     Diagnosing Intelligence Failures
     Regulating Cryptography
     Terrorists and Steganography
     Protecting Privacy and Liberty
     How to Help

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The Attacks  [back to top]

Watching the television on September 11, my primary reaction was amazement.

The attacks were amazing in their diabolicalness and audacity: to hijack fuel-laden commercial airliners and fly them into buildings,
killing thousands of innocent civilians.  We'll probably never know if the attackers realized that the heat from the jet fuel would melt
the steel supports and collapse the World Trade Center.  It seems probable that they placed advantageous trades on the world's
stock markets just before the attack.  No one planned for an attack like this.  We like to think that human beings don't make plans
like this.

I was impressed when al-Qaeda simultaneously bombed two American embassies in Africa.  I was more impressed when they blew a
40-foot hole in an American warship.  This attack makes those look like minor operations.

The attacks were amazing in their complexity.  Estimates are that the plan required about 50 people, at least 19 of them willing to
die.  It required training.  It required logistical support.  It required coordination.  The sheer scope of the attack seems beyond the
capability of a terrorist organization.

The attacks rewrote the hijacking rule book.  Responses to hijackings are built around this premise: get the plane on the ground so
negotiations can begin.  That's obsolete now.

They rewrote the terrorism book, too.  Al-Qaeda invented a new type of attacker.  Historically, suicide bombers are young, single,
fanatical, and have nothing to lose.  These people were older and more experienced.  They had marketable job skills.  They lived in
the U.S.: watched television, ate fast food, drank in bars.  One left a wife and four children.

It was also a new type of attack.  One of the most difficult things about a terrorist operation is getting away.  This attack neatly
solved that problem.  It also solved the technological problem.  The United States spends billions of dollars on remote-controlled
precision-guided munitions; al-Qaeda just finds morons willing to fly planes into skyscrapers.

Finally, the attacks were amazing in their success.  They weren't perfect.  We know that 100% of the attempted hijackings were
successful, and 75% of the hijacked planes successfully hit their targets.  We don't know how many planned hijackings were aborted
for one reason or another.  What's most amazing is that the plan wasn't leaked.  No one successfully defected.  No one slipped up
and gave the plan away.  Al-Qaeda had assets in the U.S. for months, and managed to keep the plan secret.  Often law enforcement
has been lucky here; in this case we weren't.

Rarely do you see an attack that changes the world's conception of attack, as these terrorist attacks changed the world's conception
of what a terrorist attack can do.  Nothing they did was novel, yet the attack was completely new.  And our conception of defense
must change as well.

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Airline Security Regulations   [back to top]

Computer security experts have a lot of expertise that can be applied to the real world.  First and foremost, we have well-developed
senses of what security looks like.  We can tell the difference between real security and snake oil.  And the new airport security rules,
put in place after September 11, look and smell a whole lot like snake oil.

All the warning signs are there: new and unproven security measures, no real threat analysis, unsubstantiated security claims.  The
ban on cutting instruments is a perfect example.  It's a knee-jerk reaction: the terrorists used small knives and box cutters, so we
must ban them.  And nail clippers, nail files, cigarette lighters, scissors (even small ones), tweezers, etc.  But why isn't anyone
asking the real questions: what is the threat, and how does turning an airplane into a kindergarten classroom reduce the threat?  If
the threat is hijacking, then the countermeasure doesn't protect against all the myriad of ways people can subdue the pilot and crew.
Hasn't anyone heard of karate?  Or broken bottles?  Think about hiding small blades inside luggage.  Or composite knives that don't
show up on metal detectors.

Parked cars now must be 300 feet from airport gates.  Why?  What security problem does this solve?  Why doesn't the same problem
imply that passenger drop-off and pick-up should also be that far away?  Curbside check-in has been eliminated.  What's the threat
that this security measure has solved?  Why, if the new threat is hijacking, are we suddenly worried about bombs?

The rule limiting concourse access to ticketed passengers is another one that confuses me.  What exactly is the threat here?
Hijackers have to be on the planes they're trying to hijack to carry out their attack, so they have to have tickets.  And anyone can call and "name their own price" for concourse access.

Increased inspections -- of luggage, airplanes, airports -- seem like a good idea, although it's far from perfect.  The biggest problem
here is that the inspectors are poorly paid and, for the most part, poorly educated and trained.  Other problems include the myriad
ways to bypass the checkpoints -- numerous studies have found all sorts of violations -- and the impossibility of effectively inspecting
everybody while maintaining the required throughput.  Unidentified armed guards on select flights is another mildly effective idea: it's
a small deterrent, because you never know if one is on the flight you want to hijack.

Positive bag matching -- ensuring that a piece of luggage does not get loaded on the plane unless its owner boards the plane -- is
actually a good security measure, but assumes that bombers have self-preservation as a guiding force.  It is completely useless
against suicide bombers.

The worst security measure of them all is the photo ID requirement.  This solves no security problem I can think of.  It doesn't even
identify people; any high school student can tell you how to get a fake ID.  The requirement for this invasive and ineffective security
measure is secret; the FAA won't send you the written regulations if you ask.  Airlines are actually more stringent about this than the
FAA requires, because the "security" measure solves a business problem for them.

The real point of photo ID requirements is to prevent people from reselling tickets.  Nonrefundable tickets used to be regularly
advertised in the newspaper classifieds.  Ads would read something like "Round trip, Boston to Chicago, 11/22 - 11/30, female, $50."
Since the airlines didn't check ID but could notice gender, any female could buy the ticket and fly the route.  Now this doesn't work.
The airlines love this; they solved a problem of theirs, and got to blame the solution on FAA security requirements.

Airline security measures are primarily designed to give the appearance of good security rather than the actuality.  This makes sense,
once you realize that the airlines' goal isn't so much to make the planes hard to hijack, as to make the passengers willing to fly.  Of
course airlines would prefer it if all their flights were perfectly safe, but actual hijackings and bombings are rare events and they know

This is not to say that all airport security is useless, and that we'd be better off doing nothing.  All security measures have benefits,
and all have costs: money, inconvenience, etc.  I would like to see some rational analysis of the costs and benefits, so we can get
the most security for the resources we have.

One basic snake-oil warning sign is the use of self-invented security measures, instead of expert-analyzed and time-tested ones.  The
closest the airlines have to experienced and expert analysis is El Al.  Since 1948 they have been operating in and out of the most
heavily terroristic areas of the planet, with phenomenal success.  They implement some pretty heavy security measures.  One thing
they do is have reinforced, locked doors between their airplanes' cockpit and the passenger section.  (Notice that this security
measure is 1) expensive, and 2) not immediately perceptible to the passenger.)  Another thing they do is place all cargo in
decompression chambers before takeoff, to trigger bombs set to sense altitude.  (Again, this is 1) expensive, and 2) imperceptible, so
unattractive to American airlines.)  Some of the things El Al does are so intrusive as to be unconstitutional in the U.S., but they let
you take your pocketknife on board with you.

Airline security:

FAA on new security rules:

A report on the rules' effectiveness:
< ve_eluded_airport_monitors+.shtml>

El Al's security measures:

More thoughts on this topic:

Two secret FAA documents on photo ID requirement, in text and GIF:

Passenger profiling:

A CATO Institute report: "The Cost of Antiterrorist Rhetoric," written well before September 11:

I don't know if this is a good idea, but at least someone is thinking about the problem:

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Biometrics in Airports   [back to top]

You have to admit, it sounds like a good idea.  Put cameras throughout airports and other public congregation areas, and have
automatic face-recognition software continuously scan the crowd for suspected terrorists.  When the software finds one, it alerts the
authorities, who swoop down and arrest the bastards.  Voila, we're safe once again.

Reality is a lot more complicated; it always is.  Biometrics is an effective authentication tool, and I've written about it before.  There
are three basic kinds of authentication: something you know (password, PIN code, secret handshake), something you have (door key,
physical ticket into a concert, signet ring), and something you are (biometrics).  Good security uses at least two different
authentication types: an ATM card and a PIN code, computer access using both a password and a fingerprint reader, a security badge
that includes a picture that a guard looks at.  Implemented properly, biometrics can be an effective part of an access control system.

I think it would be a great addition to airport security: identifying airline and airport personnel such as pilots, maintenance workers,
etc.  That's a problem biometrics can help solve.  Using biometrics to pick terrorists out of crowds is a different kettle of fish.

In the first case (employee identification), the biometric system has a straightforward problem: does this biometric belong to the
person it claims to belong to?  In the latter case (picking terrorists out of crowds), the system needs to solve a much harder problem:
does this biometric belong to anyone in this large database of people?  The difficulty of the latter problem increases the complexity of
the identification, and leads to identification failures.

Setting up the system is different for the two applications.  In the first case, you can unambiguously know the reference biometric
belongs to the correct person.  In the latter case, you need to continually worry about the integrity of the biometric database.  What
happens if someone is wrongfully included in the database?  What kind of right of appeal does he have?

Getting reference biometrics is different, too.  In the first case, you can initialize the system with a known, good biometric.  If the
biometric is face recognition, you can take good pictures of new employees when they are hired and enter them into the system.
Terrorists are unlikely to pose for photo shoots.  You might have a grainy picture of a terrorist, taken five years ago from 1000 yards
away when he had a beard.  Not nearly as useful.

But even if all these technical problems were magically solved, it's still very difficult to make this kind of system work.  The hardest
problem is the false alarms.  To explain why, I'm going to have to digress into statistics and explain the base rate fallacy.

Suppose this magically effective face-recognition software is 99.99 percent accurate.  That is, if someone is a terrorist, there is a
99.99 percent chance that the software indicates "terrorist," and if someone is not a terrorist, there is a 99.99 percent chance that the
software indicates "non-terrorist."  Assume that one in ten million flyers, on average, is a terrorist.  Is the software any good?

No.  The software will generate 1000 false alarms for every one real terrorist.  And every false alarm still means that all the security
people go through all of their security procedures.  Because the population of non-terrorists is so much larger than the number of
terrorists, the test is useless.  This result is counterintuitive and surprising, but it is correct.  The false alarms in this kind of system
render it mostly useless.  It's "The Boy Who Cried Wolf" increased 1000-fold.

I say mostly useless, because it would have some positive effect.  Once in a while, the system would correctly finger a frequent-flyer
terrorist.  But it's a system that has enormous costs: money to install, manpower to run, inconvenience to the millions of people
incorrectly identified, successful lawsuits by some of those people, and a continued erosion of our civil liberties.  And all the false
alarms will inevitably lead those managing the system to distrust its results, leading to sloppiness and potentially costly mistakes.
Ubiquitous harvesting of biometrics might sound like a good idea, but I just don't think it's worth it.

Phil Agre on face-recognition biometrics:

My original essay on biometrics:

Face recognition useless in airports:
According to a DARPA study, to detect 90 per cent of terrorists we'd need to raise an alarm for one in every three people passing
through the airport.

A company that is pushing this idea:

A version of this article was published here:

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Diagnosing Intelligence Failures   [back to top]

It's clear that U.S. intelligence failed to provide adequate warning of the September 11 terrorist attacks, and that the FBI failed to
prevent the attacks.  It's also clear that there were all sorts of indications that the attacks were going to happen, and that there were
all sorts of things that we could have noticed but didn't.  Some have claimed that this was a massive intelligence failure, and that we
should have known about and prevented the attacks.  I am not convinced.

There's a world of difference between intelligence data and intelligence information.  In what I am sure is the mother of all
investigations, the CIA, NSA, and FBI have uncovered all sorts of data from their files, data that clearly indicates that an attack was
being planned.  Maybe it even clearly indicates the nature of the attack, or the date.  I'm sure lots of information is there, in files,
intercepts, computer memory.

Armed with the clarity of hindsight, it's easy to look at all the data and point to what's important and relevant.  It's even easy to take
all that important and relevant data and turn it into information.  And it's real easy to take that information and construct a picture of
what's going on.

It's a lot harder to do before the fact.  Most data is irrelevant, and most leads are false ones.  How does anyone know which is the
important one, that effort should be spent on this specific threat and not the thousands of others?

So much data is collected -- the NSA sucks up an almost unimaginable quantity of electronic communications, the FBI gets
innumerable leads and tips, and our allies pass all sorts of information to us -- that we can't possibly analyze it all.  Imagine
terrorists are hiding plans for attacks in the text of books in a large university library; you have no idea how many plans there are or
where they are, and the library expands faster than you can possibly read it.  Deciding what to look at is an impossible task, so a lot
of good intelligence goes unlearned.

We also don't have any context to judge the intelligence effort.  How many terrorist attempts have been thwarted in the past year?
How many groups are being tracked?  If the CIA, NSA, and FBI succeed, no one ever knows.  It's only in failure that they get any

And it was a failure.  Over the past couple of decades, the U.S. has relied more and more on high-tech electronic eavesdropping
(SIGINT and COMINT) and less and less on old fashioned human intelligence (HUMINT).  This only makes the analysis problem worse:
too much data to look at, and not enough real-world context.  Look at the intelligence failures of the past few years: failing to predict
India's nuclear test, or the attack on the USS Cole, or the bombing of the two American embassies in Africa; concentrating on Wen Ho
Lee to the exclusion of the real spies, like Robert Hanssen.

But whatever the reason, we failed to prevent this terrorist attack.  In the post mortem, I'm sure there will be changes in the way we
collect and (most importantly) analyze anti-terrorist data.  But calling this a massive intelligence failure is a disservice to those who
are working to keep our country secure.

Intelligence failure is an overreliance on eavesdropping and not enough on human intelligence:

Another view:

Too much electronic eavesdropping only makes things harder:

Israel alerted the U.S. about attacks:
Mostly retracted:

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Regulating Cryptography   [back to top]

In the wake of the devastating attacks on New York's World Trade Center and the Pentagon, Senator Judd Gregg and other
high-ranking government officials quickly seized on the opportunity to resurrect limits on strong encryption and key escrow systems
that ensure government access to encrypted messages.

I think this is a bad move.  It will do little to thwart terrorist activities, while at the same time significantly reducing the security of
our own critical infrastructure.  We've been through these arguments before, but legislators seem to have short memories.  Here's
why trying to limit cryptography is bad for Internet security.

One, you can't limit the spread of cryptography.  Cryptography is mathematics, and you can't ban mathematics.  All you can ban is a
set of products that use that mathematics, but that is something quite different.  Years ago, during the cryptography debates, an
international crypto survey was completed; it listed almost a thousand products with strong cryptography from over a hundred
countries.  You might be able to control cryptography products in a handful of industrial countries, but that won't prevent criminals
from importing them.  You'd have to ban them in every country, and even then it won't be enough.  Any terrorist organization with a
modicum of skill can write its own cryptography software.  And besides, what terrorist is going to pay attention to a legal ban?

Two, any controls on the spread of cryptography hurt more than they help.  Cryptography is one of the best security tools we have to
protect our electronic world from harm: eavesdropping, unauthorized access, meddling, denial of service.  Sure, by controlling the
spread of cryptography you might be able to prevent some terrorist groups from using cryptography, but you'll also prevent bankers,
hospitals, and air-traffic controllers from using it.  (And, remember, the terrorists can always get the stuff elsewhere: see my first
point.)  We've got a lot of electronic infrastructure to protect, and we need all the cryptography we can get our hands on.  If anything,
we need to make strong cryptography more prevalent if companies continue to put our planet's critical infrastructure online.

Three, key escrow doesn't work.  Short refresher: this is the notion that companies should be forced to implement back doors in crypto
products such that law enforcement, and only law enforcement, can peek in and eavesdrop on encrypted messages.  Terrorists and
criminals won't use it.  (Again, see my first point.)

Key escrow also makes it harder for the good guys to secure the important stuff.  All key-escrow systems require the existence of a
highly sensitive and highly available secret key or collection of keys that must be maintained in a secure manner over an extended
time period.  These systems must make decryption information quickly accessible to law enforcement agencies without notice to the
key owners.  Does anyone really think that we can build this kind of system securely?  It would be a security engineering task of
unbelievable magnitude, and I don't think we have a prayer of getting it right.  We can't build a secure operating system, let alone a
secure computer and secure network.

Stockpiling keys in one place is a huge risk just waiting for attack or abuse.  Whose digital security do you trust absolutely and
without question, to protect every major secret of the nation?  Which operating system would you use?  Which firewall?  Which
applications?  As attractive as it may sound, building a workable key-escrow system is beyond the current capabilities of computer

Years ago, a group of colleagues and I wrote a paper outlining why key escrow is a bad idea.  The arguments in the paper still stand,
and I urge everyone to read it.  It's not a particularly technical paper, but it lays out all the problems with building a secure, effective,
scalable key-escrow infrastructure.

The events of September 11 have convinced a lot of people that we live in dangerous times, and that we need more security than
ever before.  They're right; security has been dangerously lax in many areas of our society, including cyberspace.  As more and more
of our nation's critical infrastructure goes digital, we need to recognize cryptography as part of the solution and not as part of the

My old "Risks of Key Recovery" paper:

Articles on this topic:

Al-Qaeda did not use encryption to plan these attacks:

Poll indicates that 72 percent of Americans believe that anti-encryption laws would be "somewhat" or "very" helpful in preventing a
repeat of last week's terrorist attacks on New York's World Trade Center and the Pentagon in Washington, D.C.  No indication of what
percentage actually understood the question.

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Terrorists and Steganography   [back to top]

Guess what?  Al-Qaeda may use steganography.  According to nameless "U.S. officials and experts" and "U.S. and foreign officials,"
terrorist groups are "hiding maps and photographs of terrorist targets and posting instructions for terrorist activities on sports chat
rooms, pornographic bulletin boards and other Web sites."

I've written about steganography in the past, and I don't want to spend much time retracing old ground.  Simply, steganography is
the science of hiding messages in messages.  Typically, a message (either plaintext or, more cleverly, ciphertext) is encoded as tiny
changes to the color of the pixels of a digital photograph.  Or in imperceptible noise in an audio file.  To the uninitiated observer, it's
just a picture.  But to the sender and receiver, there's a message hiding in there.

It doesn't surprise me that terrorists are using this trick.  The very aspects of steganography that make it unsuitable for normal
corporate use make it ideally suited for terrorist use.  Most importantly, it can be used in an electronic dead drop.

If you read the FBI affidavit against Robert Hanssen, you learn how Hanssen communicated with his Russian handlers.  They never
met, but would leave messages, money, and documents for one another in plastic bags under a bridge.  Hanssen's handler would
leave a signal in a public place -- a chalk mark on a mailbox -- to indicate a waiting package.  Hanssen would later collect the

That's a dead drop.  It has many advantages over a face-to-face meeting.  One, the two parties are never seen together.  Two, the
two parties don't have to coordinate a rendezvous.  Three, and most importantly, one party doesn't even have to know who the other
one is (a definite advantage if one of them is arrested).  Dead drops can be used to facilitate completely anonymous, asynchronous

Using steganography to embed a message in a pornographic image and posting it to a Usenet newsgroup is the cyberspace equivalent
of a dead drop.  To everyone else, it's just a picture.  But to the receiver, there's a message in there waiting to be extracted.

To make it work in practice, the terrorists would need to set up some sort of code.  Just as Hanssen knew to collect his package when
he saw the chalk mark, a virtual terrorist will need to know to look for his message. (He can't be expected to search every picture.)
There are lots of ways to communicate a signal: timestamp on the message, an uncommon word in the subject line, etc.  Use your
imagination here; the possibilities are limitless.

The effect is that the sender can transmit a message without ever communicating directly with the receiver.  There is no e-mail
between them, no remote logins, no instant messages.  All that exists is a picture posted to a public forum, and then downloaded by
anyone sufficiently enticed by the subject line (both third parties and the intended receiver of the secret message).

So, what's a counter-espionage agency to do?  There are the standard ways of finding steganographic messages, most of which
involve looking for changes in traffic patterns.  If Bin Laden is using pornographic images to embed his secret messages, it is unlikely
these pictures are being taken in Afghanistan.  They're probably downloaded from the Web.  If the NSA can keep a database of
images (wouldn't that be something?), then they can find ones with subtle changes in the low-order bits.  If Bin Laden uses the same
image to transmit multiple messages, the NSA could notice that.  Otherwise, there's probably nothing the NSA can do.  Dead drops,
both real and virtual, can't be prevented.

Why can't businesses use this?  The primary reason is that legitimate businesses don't need dead drops.  I remember hearing one
company talk about a corporation embedding a steganographic message to its salespeople in a photo on the corporate Web page.
Why not just send an encrypted e-mail?  Because someone might notice the e-mail and know that the salespeople all got an
encrypted message.  So send a message every day: a real message when you need to, and a dummy message otherwise.  This is a
traffic analysis problem, and there are other techniques to solve it.  Steganography just doesn't apply here.

Steganography is good way for terrorist cells to communicate, allowing communication without any group knowing the identity of the
other.  There are other ways to build a dead drop in cyberspace.  A spy can sign up for a free, anonymous e-mail account, for
example.  Bin Laden probably uses those too.

News articles:
< intell.DTL>

My old essay on steganography:

Study claims no steganography on eBay:

Detecting steganography on the Internet:

A version of this essay appeared on ZDnet:

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News   [back to top]

I am not opposed to using force against the terrorists.  I am not opposed to going to war -- for retribution, deterrence, and the
restoration of the social contract -- assuming a suitable enemy can be identified.  Occasionally, peace is something you have to fight
for.  But I think the use of force is far more complicated than most people realize.  Our actions are important; messing this up will
only make things worse.

Written before September 11: A former CIA operative explains why the terrorist Usama bin Laden has little to fear from American
And a Russian soldier discusses why war in Afghanistan will be a nightmare.
A British soldier explains the same:
Lessons from Britain on fighting terrorism:
1998 Esquire interview with Bin Ladin:

Phil Agre's comments on these issues:

Why technology can't save us:

Hactivism exacts revenge for terrorist attacks:
FBI reminds everyone that it's illegal:

Hackers face life imprisonment under anti-terrorism act:
Especially scary are the "advice or assistance" components.  A security consultant could face life imprisonment, without parole, if he
discovered and publicized a security hole that was later exploited by someone else.  After all, without his "advice" about what the
hole was, the attacker never would have accomplished his hack.

Companies fear cyberterrorism:
They're investing in security:

Upgrading government computers to fight terrorism:

Risks of cyberterrorism attacks against our electronic infrastructure:
< ef=1732900718>

Now the complaint is that Bin Laden is NOT using high-tech communications:

Larry Ellison is willing to give away the software to implement a national ID card.
Security problems include: inaccurate information, insiders issuing fake cards (this happens with state drivers' licenses), vulnerability
of the large database, potential privacy abuses, etc.  And, of course, no trans-national terrorists would be listed in such a system,
because they wouldn't be U.S. citizens.  What do you expect from a company whose origins are intertwined with the CIA?

** *** ***** ******* *********** *************

Protecting Privacy and Liberty   [back to top]

Appalled by the recent hijackings, many Americans have declared themselves willing to give up civil liberties in the name of security.
They've declared it so loudly that this trade-off seems to be a fait accompli.  Article after article talks about the balance between
privacy and security, discussing whether various increases of security are worth the privacy and civil-liberty losses.  Rarely do I see a
discussion about whether this linkage is a valid one.

Security and privacy are not two sides of a teeter-totter.  This association is simplistic and largely fallacious.  It's easy and fast, but
less effective, to increase security by taking away liberty.  However, the best ways to increase security are not at the expense of
privacy and liberty.

It's easy to refute the notion that all security comes at the expense of liberty.  Arming pilots, reinforcing cockpit doors, and teaching
flight attendants karate are all examples of security measures that have no effect on individual privacy or liberties.  So are better
authentication of airport maintenance workers, or dead-man switches that force planes to automatically land at the closest airport, or
armed air marshals traveling on flights.

Liberty-depriving security measures are most often found when system designers failed to take security into account from the
beginning.  They're Band-aids, and evidence of bad security planning.  When security is designed into a system, it can work without
forcing people to give up their freedoms.

Here's an example: securing a room.  Option one: convert the room into an impregnable vault.  Option two: put locks on the door,
bars on the windows, and alarm everything.  Option three: don't bother securing the room; instead, post a guard in the room who
records the ID of everyone entering and makes sure they should be allowed in.

Option one is the best, but is unrealistic.  Impregnable vaults just don't exist, getting close is prohibitively expensive, and turning a
room into a vault greatly lessens its usefulness as a room.  Option two is the realistic best; combine the strengths of prevention,
detection, and response to achieve resilient security.  Option three is the worst.  It's far more expensive than option two, and the
most invasive and easiest to defeat of all three options.  It's also a sure sign of bad planning; designers built the room, and only
then realized that they needed security.  Rather then spend the effort installing door locks and alarms, they took the easy way out
and invaded people's privacy.

A more complex example is Internet security.  Preventive countermeasures help significantly against script kiddies, but fail against
smart attackers.  For a couple of years I have advocated detection and response to provide security on the Internet.  This works; my
company catches attackers -- both outside hackers and insiders -- all the time.  We do it by monitoring the audit logs of network
products: firewalls, IDSs, routers, servers, and applications.  We don't eavesdrop on legitimate users or read traffic.  We don't invade
privacy.  We monitor data about data, and find abuse that way.  No civil liberties are violated.  It's not perfect, but nothing is.  Still,
combined with preventive security products it is more effective, and more cost-effective, than anything else.

The parallels between Internet security and global security are strong.  All criminal investigation looks at surveillance records.  The
lowest-tech version of this is questioning witnesses.  In this current investigation, the FBI is looking at airport videotapes, airline
passenger records, flight school class records, financial records, etc.  And the better job they can do examining these records, the
more effective their investigation will be.

There are copycat criminals and terrorists, who do what they've seen done before.  To a large extent, this is what the hastily
implemented security measures have tried to prevent.  And there are the clever attackers, who invent new ways to attack people.
This is what we saw on September 11.  It's expensive, but we can build security to protect against yesterday's attacks.  But we can't
guarantee protection against tomorrow's attacks: the hacker attack that hasn't been invented, or the terrorist attack yet to be

Demands for even more surveillance miss the point.  The problem is not obtaining data, it's deciding which data is worth analyzing
and then interpreting it.  Everyone already leaves a wide audit trail as we go through life, and law enforcement can already access
those records with search warrants.  The FBI quickly pieced together the terrorists' identities and the last few months of their lives,
once they knew where to look.  If they had thrown up their hands and said that they couldn't figure out who did it or how, they might
have a case for needing more surveillance data.  But they didn't, and they don't.

More data can even be counterproductive.  The NSA and the CIA have been criticized for relying too much on signals intelligence, and
not enough on human intelligence.  The East German police collected data on four million East Germans, roughly a quarter of their
population.  Yet they did not foresee the peaceful overthrow of the Communist government because they invested heavily in data
collection instead of data interpretation.  We need more intelligence agents squatting on the ground in the Middle East arguing the
Koran, not sitting in Washington arguing about wiretapping laws.

People are willing to give up liberties for vague promises of security because they think they have no choice.  What they're not being
told is that they can have both.  It would require people to say no to the FBI's power grab.  It would require us to discard the easy
answers in favor of thoughtful answers.  It would require structuring incentives to improve overall security rather than simply
decreasing its costs.  Designing security into systems from the beginning, instead of tacking it on at the end, would give us the
security we need, while preserving the civil liberties we hold dear.

Some broad surveillance, in limited circumstances, might be warranted as a temporary measure.  But we need to be careful that it
remain temporary, and that we do not design surveillance into our electronic infrastructure.  Thomas Jefferson once said:  "Eternal
vigilance is the price of liberty."  Historically, liberties have always been a casualty of war, but a temporary casualty.  This war -- a
war without a clear enemy or end condition -- has the potential to turn into a permanent state of society.  We need to design our
security accordingly.

The events of September 11th demonstrated the need for America to redesign our public infrastructures for security.  Ignoring this
need would be an additional tragedy.

Quotes from U.S. government officials on the need to preserve liberty during this crisis:

Quotes from editorial pages on the same need:

Selected editorials:

Schneier's comments in the UK:

War and liberties:

More on Ashcroft's anti-privacy initiatives:

Editorial cartoon:

Terrorists leave a broad electronic trail:

National Review article from 1998: "Know nothings: U.S. intelligence failures stem from too much information, not enough

A previous version of this essay appeared in the San Jose Mercury News:

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How to Help  [back to top]

How can you help?  Speak about the issues.  Write to your elected officials.  Contribute to organizations working on these issues.

This week the United States Congress will act on the most sweeping proposal to extend the surveillance authority of the government
since the end of the Cold War. If you value privacy, there are three steps you should take before you open your next email message:

1. Urge your representatives in Congress to protect privacy.
- Call the White House switchboard at 202-224-3121.
- Ask to be connected to the office of your Congressional representative.
- When you are put through, say "May I please speak to the staff member who is working on the anti-terrorism legislation?" If that
person is not available to speak with you, say  "May I please leave a message?"
- Briefly explain that you appreciate the efforts of your representative to address the challenges brought about by the September 11th
tragedy, but it is your view that it would be a mistake to make any changes in the federal wiretap statute that do not respond to "the
immediate threat of investigating or preventing terrorist acts."

2. Go to the In Defense of Freedom web site and endorse the statement:  <>

3. Forward this message to at least five other people.

We have less than 100 hours before Congress acts on legislation that will (a) significantly expand the use of Carnivore, (b) make
computer hacking a form of terrorism, (c) expand electronic surveillance in routine criminal investigations, and (d) reduce government

Please act now.

More generally, I expect to see many pieces of legislation that will address these matters.  Visit the following Web sites for
up-to-date information on what is happening and what you can do to help.

The Electronic Privacy Information Center:

The Center for Democracy and Technology:

The American Civil Liberties Union:

** *** ***** ******* *********** *************

CRYPTO-GRAM is a free monthly newsletter providing summaries, analyses, insights, and commentaries on computer security and
cryptography.  Back issues are available on <>.

To subscribe, visit <> or send a blank message to  To unsubscribe, visit <>.

Please feel free to forward CRYPTO-GRAM to colleagues and friends who will find it valuable.  Permission is granted to reprint
CRYPTO-GRAM, as long as it is reprinted in its entirety.

CRYPTO-GRAM is written by Bruce Schneier.  Schneier is founder and CTO of Counterpane Internet Security Inc., the author of "Secrets
and Lies" and "Applied Cryptography," and an inventor of the Blowfish, Twofish, and Yarrow algorithms.  He is a member of the
Advisory Board of the Electronic Privacy Information Center (EPIC).  He is a frequent writer and lecturer on computer security and

Counterpane Internet Security, Inc. is the world leader in Managed Security Monitoring.  Counterpane's expert security analysts protect
networks for Fortune 1000 companies world-wide.


Copyright (c) 2001 by Counterpane Internet Security, Inc.

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