Schneier on Security

A blog covering security and security technology.

Friday Squid Blogging: Office Squid

Office squid.

Posted on July 3, 2009 at 4:31 PM • 0 Comments • View Blog Reactions

The Pros and Cons of Password Masking

Usability guru Jakob Nielsen opened up a can of worms when he made the case for unmasking passwords in his blog. I chimed in that I agreed. Almost 165 comments on my blog (and several articles, essays, and many other blog posts) later, the consensus is that we were wrong.

I was certainly too glib. Like any security countermeasure, password masking has value. But like any countermeasure, password masking is not a panacea. And the costs of password masking need to be balanced with the benefits.

The cost is accuracy. When users don't get visual feedback from what they're typing, they're more prone to make mistakes. This is especially true with character strings that have non-standard characters and capitalization. This has several ancillary costs:

• Users get pissed off.
• Users are more likely to choose easy-to-type passwords, reducing both mistakes and security. Removing password masking will make people more comfortable with complicated passwords: they'll become easier to memorize and easier to use.

The benefits of password masking are more obvious:

• Security from shoulder surfing. If people can't look over your shoulder and see what you're typing, they're much less likely to be able to steal your password. Yes, they can look at your fingers instead, but that's much harder than looking at the screen. Surveillance cameras are also an issue: it's easier to watch someone's fingers on recorded video, but reading a cleartext password off a screen is trivial.

  In some situations, there is a trust dynamic involved. Do you type your password while your boss is standing over your shoulder watching? How about your spouse or partner? Your parent or child? Your teacher or students? At ATMs, there's a social convention of standing away from someone using the machine, but that convention doesn't apply to computers. You might not trust the person standing next to you enough to let him see your password, but don't feel comfortable telling him to look away. Password masking solves that social awkwardness.

• Security from screen scraping malware. This is less of an issue; keyboard loggers are more common and unaffected by password masking. And if you have that kind of malware on your computer, you've got all sorts of problems.

• A security "signal." Password masking alerts users, and I'm thinking users who aren't particularly security savvy, that passwords are a secret.

I believe that shoulder surfing isn't nearly the problem it's made out to be. One, lots of people use their computers in private, with no one looking over their shoulders. Two, personal handheld devices are used very close to the body, making shoulder surfing all that much harder. Three, it's hard to quickly and accurately memorize a random non-alphanumeric string that flashes on the screen for a second or so.

This is not to say that shoulder surfing isn't a threat. It is. And, as many readers pointed out, password masking is one of the reasons it isn't more of a threat. And the threat is greater for those who are not fluent computer users: slow typists and people who are likely to choose bad passwords. But I believe that the risks are overstated.

Password masking is definitely important on public terminals with short PINs. (I'm thinking of ATMs.) The value of the PIN is large, shoulder surfing is more common, and a four-digit PIN is easy to remember in any case.

And lastly, this problem largely disappears on the Internet on your personal computer. Most browsers include the ability to save and then automatically populate password fields, making the usability problem go away at the expense of another security problem (the security of the password becomes the security of the computer). There's a Firefox plugin that gets rid of password masking. And programs like my own Password Safe allow passwords to be cut and pasted into applications, also eliminating the usability problem.

One approach is to make it a configurable option. High-risk banking applications could turn password masking on by default; other applications could turn it off by default. Browsers in public locations could turn it on by default. I like this, but it complicates the user interface.

A reader mentioned BlackBerry's solution, which is to display each character briefly before masking it; that seems like an excellent compromise.

I, for one, would like the option. I cannot type complicated WEP keys into Windows -- twice! what's the deal with that? -- without making mistakes. I cannot type my rarely used and very complicated PGP keys without making a mistake unless I turn off password masking. That's what I was reacting to when I said "I agree."

So was I wrong? Maybe. Okay, probably. Password masking definitely improves security; many readers pointed out that they regularly use their computer in crowded environments, and rely on password masking to protect their passwords. On the other hand, password masking reduces accuracy and makes it less likely that users will choose secure and hard-to-remember passwords, I will concede that the password masking trade-off is more beneficial than I thought in my snap reaction, but also that the answer is not nearly as obvious as we have historically assumed.

Posted on July 3, 2009 at 1:42 PM • 39 Comments • View Blog Reactions

The Insecurity of Secrecy

Good essay -- "The Staggering Cost of Playing it 'Safe'" -- about the political motivations for terrorist security policy.

Senator Barbara Boxer has led an effort to at least put together a public database of ash storage sites so that people can judge the risk to the areas where they live. However, even this effort has been blocked not by coal companies or utilities, but by the DHS. How could it possibly be a national security interest to cover up the location of material that's "not toxic or anything?" It's not. In fact, even if the ash turns out to be as bad as its worst critics fear, blocking the database is far more dangerous than revealing the location of these sites. Not only has there not been any threat against these sites by terrorists, and no workable scenario by which they might cause a problem, coal slurry impoundments are already failing with regularity, dousing parts of America with millions of gallons of this material. It doesn't take terrorists to make this happen.

Blocking the release of this information doesn't protect the citizens of the United States in any way. It's just another example of the same creeping secrecy that makes cities more difficult to manage because of secrecy over facilities. The same creeping secrecy that "blurs" national monuments from images and puts intentional gaps in public information. The same creeping secrecy that increasingly elevates the most unlikely attack -- the shoe bombers of the world -- above our right to know what's going on around us so that we can make informed decisions. The same secrecy that defends torturers.

Posted on July 3, 2009 at 7:18 AM • 16 Comments • View Blog Reactions

Information Leakage from Keypads

Can anyone guess the entry codes for these door locks?

There are 10,000 possible four-digit codes, but you only have to try 24 on these keypads. The first is most likely 1986 or 1968. The second is almost certainly 1234.

Posted on July 2, 2009 at 12:09 PM • 57 Comments • View Blog Reactions

More Security Countermeasures from the Natural World

The plant caladium steudneriifolium pretends to be ill so mining moths won't eat it.

She believes that the plant essentially fakes being ill, producing variegated leaves that mimic those that have already been damaged by mining moth larvae. That deters the moths from laying any further larvae on the leaves, as the insects assume the previous caterpillars have already eaten most of the leaves' nutrients.

Cabbage aphids arm themselves with chemical bombs:

Its body carries two reactive chemicals that only mix when a predator attacks it. The injured aphid dies. But in the process, the chemicals in its body react and trigger an explosion that delivers lethal amounts of poison to the predator, saving the rest of the colony.

The dark-footed ant spider mimics an ant so that it's not eaten by other spiders, and so it can eat spiders itself:

M.melanotarsa is a jumping spider that protects itself from predators (like other jumping spiders) by resembling an ant. Earlier this month, Ximena Nelson and Robert Jackson showed that they bolster this illusion by living in silken apartment complexes and travelling in groups, mimicking not just the bodies of ants but their social lives too.

Now Nelson and Robert are back with another side to the ant-spider's tale - it also uses its impersonation for attack as well as defence. It also feasts on the eggs and youngsters of the very same spiders that its ant-like form protects it from. It is, essentially, a spider that looks like an ant to avoid being eaten by spiders so that it itself can eat spiders.

My previous post about security stories from the insect world.

Posted on July 2, 2009 at 6:11 AM • 15 Comments • View Blog Reactions

MD6 Withdrawn from SHA-3 Competition

In other SHA-3 news, Ron Rivest seems to have withdrawn MD6 from the SHA-3 competition. From an e-mail to a NIST mailing list:

We suggest that MD6 is not yet ready for the next SHA-3 round, and we also provide some suggestions for NIST as the contest moves forward.

Basically, the issue is that in order for MD6 to be fast enough to be competitive, the designers have to reduce the number of rounds down to 30-40, and at those rounds, the algorithm loses its proofs of resistance to differential attacks.

Thus, while MD6 appears to be a robust and secure cryptographic hash algorithm, and has much merit for multi-core processors, our inability to provide a proof of security for a reduced-round (and possibly tweaked) version of MD6 against differential attacks suggests that MD6 is not ready for consideration for the next SHA-3 round.

EDITED TO ADD (7/1): This is a very classy withdrawal, as we expect from Ron Rivest -- especially given the fact that there are no attacks on it, while other algorithms have been seriously broken and their submitters keep trying to pretend that no one has noticed.

Posted on July 1, 2009 at 2:27 PM • 22 Comments • View Blog Reactions

New Attack on AES

There's a new cryptanalytic attack on AES that is better than brute force:

Abstract. In this paper we present two related-key attacks on the full AES. For AES-256 we show the first key recovery attack that works for all the keys and has complexity 2¹¹⁹, while the recent attack by Biryukov-Khovratovich-Nikolic works for a weak key class and has higher complexity. The second attack is the first cryptanalysis of the full AES-192. Both our attacks are boomerang attacks, which are based on the recent idea of finding local collisions in block ciphers and enhanced with the boomerang switching techniques to gain free rounds in the middle.

In an e-mail, the authors wrote:

We also expect that a careful analysis may reduce the complexities. As a preliminary result, we think that the complexity of the attack on AES-256 can be lowered from 2¹¹⁹ to about 2^110.5 data and time.

We believe that these results may shed a new light on the design of the key-schedules of block ciphers, but they pose no immediate threat for the real world applications that use AES.

Agreed. While this attack is better than brute force -- and some cryptographers will describe the algorithm as "broken" because of it -- it is still far, far beyond our capabilities of computation. The attack is, and probably forever will be, theoretical. But remember: attacks always get better, they never get worse. Others will continue to improve on these numbers. While there's no reason to panic, no reason to stop using AES, no reason to insist that NIST choose another encryption standard, this will certainly be a problem for some of the AES-based SHA-3 candidate hash functions.

Posted on July 1, 2009 at 11:49 AM • 23 Comments • View Blog Reactions

Security, Group Size, and the Human Brain

If the size of your company grows past 150 people, it's time to get name badges. It's not that larger groups are somehow less secure, it's just that 150 is the cognitive limit to the number of people a human brain can maintain a coherent social relationship with.

Primatologist Robin Dunbar derived this number by comparing neocortex -- the "thinking" part of the mammalian brain -- volume with the size of primate social groups. By analyzing data from 38 primate genera and extrapolating to the human neocortex size, he predicted a human "mean group size" of roughly 150.

This number appears regularly in human society; it's the estimated size of a Neolithic farming village, the size at which Hittite settlements split, and the basic unit in professional armies from Roman times to the present day. Larger group sizes aren't as stable because their members don't know each other well enough. Instead of thinking of the members as people, we think of them as groups of people. For such groups to function well, they need externally imposed structure, such as name badges.

Of course, badges aren't the only way to determine in-group/out-group status. Other markers include insignia, uniforms, and secret handshakes. They have different security properties and some make more sense than others at different levels of technology, but once a group reaches 150 people, it has to do something.

More generally, there are several layers of natural human group size that increase with a ratio of approximately three: 5, 15, 50, 150, 500, and 1500 -- although, really, the numbers aren't as precise as all that, and groups that are less focused on survival tend to be smaller. The layers relate to both the intensity and intimacy of relationship and the frequency of contact.

The smallest, three to five, is a "clique": the number of people from whom you would seek help in times of severe emotional distress. The twelve to 20 group is the "sympathy group": people with which you have special ties. After that, 30 to 50 is the typical size of hunter-gatherer overnight camps, generally drawn from the same pool of 150 people. No matter what size company you work for, there are only about 150 people you consider to be "co-workers." (In small companies, Alice and Bob handle accounting. In larger companies, it's the accounting department -- and maybe you know someone there personally.) The 500-person group is the "megaband," and the 1,500-person group is the "tribe." Fifteen hundred is roughly the number of faces we can put names to, and the typical size of a hunter-gatherer society.

These numbers are reflected in military organization throughout history: squads of 10 to 15 organized into platoons of three to four squads, organized into companies of three to four platoons, organized into battalions of three to four companies, organized into regiments of three to four batallions, organized into divisions of two to three regiments, and organized into corps of two to three divisions.

Coherence can become a real problem once organizations get above about 150 in size. So as group sizes grow across these boundaries, they have more externally imposed infrastructure -- and more formalized security systems. In intimate groups, pretty much all security is ad hoc. Companies smaller than 150 don't bother with name badges; companies greater than 500 hire a guard to sit in the lobby and check badges. The military have had centuries of experience with this under rather trying circumstances, but even there the real commitment and bonding invariably occurs at the company level. Above that you need to have rank imposed by discipline.

The whole brain-size comparison might be bunk, and a lot of evolutionary psychologists disagree with it. But certainly security systems become more formalized as groups grow larger and their members less known to each other. When do more formal dispute resolution systems arise: town elders, magistrates, judges? At what size boundary are formal authentication schemes required? Small companies can get by without the internal forms, memos, and procedures that large companies require; when does what tend to appear? How does punishment formalize as group size increase? And how do all these things affect group coherence? People act differently on social networking sites like Facebook when their list of "friends" grows larger and less intimate. Local merchants sometimes let known regulars run up tabs. I lend books to friends with much less formality than a public library. What examples have you seen?

An edited version of this essay, without links, appeared in the July/August 2009 issue of IEEE Security & Privacy.

Posted on July 1, 2009 at 6:51 AM • 45 Comments • View Blog Reactions

Cryptography Spam

I think this is a first.

Information security, and protection of your e-money. Electronic payments and calculations, on means of a network the Internet or by means of bank credit cards, continue to win the world market. Electronic payments, it quickly, conveniently, but is not safely. Now there is a real war, between users and hackers. Your credit card can be forgery. The virus can get into your computer. Most not pleasant, what none, cannot give you guarantees, safety.

But, this disgrace can put an end.

I have developed the program which, does impossible the fact of abduction of a passwords, countersign, and personal data of the users. In the program the technology of an artificial intellect is used. As you cannot, guess about what the person thinks. As and not possible to guess, algorithm of the program. This system to crack it is impossible.

I assure that this system, will be most popular in the near future. I wish to create the company, with branches in the different countries of the world, and I invite all interested persons.

Together we will construct very profitable business.

Posted on June 30, 2009 at 1:36 PM • 51 Comments • View Blog Reactions

Growth of the CSE

The Communication Security Establishment (CSE, basically Canada's NSA) is growing so fast they're running out of room and building new office buildings.

Posted on June 30, 2009 at 6:32 AM • 12 Comments • View Blog Reactions

Anti-Stab Knife

I've already written about the risks of pointy knives. This no-stabbing knife is the solution, and seems not to be a joke.

EDITED TO ADD (7/1): Some people have taken this blog post to imply that I am endorsing these knives. These are obviously not regular readers of mine. (For my part, I'm going to buy a very sharp and very stabby hand-made chef's knife in Kyoto today.)

Posted on June 29, 2009 at 2:18 PM • 105 Comments • View Blog Reactions

Protecting Against the Snatched Laptop Data Theft

Almost two years ago, I wrote about my strategy for encrypting my laptop. One of the things I said was:

There are still two scenarios you aren't secure against, though. You're not secure against someone snatching your laptop out of your hands as you're typing away at the local coffee shop. And you're not secure against the authorities telling you to decrypt your data for them.

Here's a free program that defends against that first threat: it locks the computer unless a key is pressed every n seconds.

Honestly, this would be too annoying for me to use, but you're welcome to try it.

Posted on June 29, 2009 at 6:51 AM • 45 Comments • View Blog Reactions

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