Schneier on Security

Privacy Salience and Social Networking Sites

schneier — 2009-07-16T06:05:11-0600

Reassuring people about privacy makes them more, not less, concerned. It's called "privacy salience," and Leslie John, Alessandro Acquisti, and George Loewenstein -- all at Carnegie Mellon University -- demonstrated this in a series of clever experiments. In one, subjects completed an online survey consisting of a series of questions about their academic behavior -- "Have you ever cheated on an exam?" for example. Half of the subjects were first required to sign a consent warning -- designed to make privacy concerns more salient -- while the other half did not. Also, subjects were randomly assigned to receive either a privacy confidentiality assurance, or no such assurance. When the privacy concern was made salient (through the consent warning), people reacted negatively to the subsequent confidentiality assurance and were less likely to reveal personal information.

In another experiment, subjects completed an online survey where they were asked a series of personal questions, such as "Have you ever tried cocaine?" Half of the subjects completed a frivolous-looking survey -- "How BAD are U??" -- with a picture of a cute devil. The other half completed the same survey with the title "Carnegie Mellon University Survey of Ethical Standards," complete with a university seal and official privacy assurances. The results showed that people who were reminded about privacy were less likely to reveal personal information than those who were not.

Privacy salience does a lot to explain social networking sites and their attitudes towards privacy. From a business perspective, social networking sites don't want their members to exercise their privacy rights very much. They want members to be comfortable disclosing a lot of data about themselves.

Joseph Bonneau and Soeren Preibusch of Cambridge University have been studying privacy on 45 popular social networking sites around the world. (You may not have realized that there are 45 popular social networking sites around the world.) They found that privacy settings were often confusing and hard to access; Facebook, with its 61 privacy settings, is the worst. To understand some of the settings, they had to create accounts with different settings so they could compare the results. Privacy tends to increase with the age and popularity of a site. General-use sites tend to have more privacy features than niche sites.

But their most interesting finding was that sites consistently hide any mentions of privacy. Their splash pages talk about connecting with friends, meeting new people, sharing pictures: the benefits of disclosing personal data.

These sites do talk about privacy, but only on hard-to-find privacy policy pages. There, the sites give strong reassurances about their privacy controls and the safety of data members choose to disclose on the site. There, the sites display third-party privacy seals and other icons designed to assuage any fears members have.

It's the Carnegie Mellon experimental result in the real world. Users care about privacy, but don't really think about it day to day. The social networking sites don't want to remind users about privacy, even if they talk about it positively, because any reminder will result in users remembering their privacy fears and becoming more cautious about sharing personal data. But the sites also need to reassure those "privacy fundamentalists" for whom privacy is always salient, so they have very strong pro-privacy rhetoric for those who take the time to search them out. The two different marketing messages are for two different audiences.

Social networking sites are improving their privacy controls as a result of public pressure. At the same time, there is a counterbalancing business pressure to decrease privacy; watch what's going on right now on Facebook, for example. Naively, we should expect companies to make their privacy policies clear to allow customers to make an informed choice. But the marketing need to reduce privacy salience will frustrate market solutions to improve privacy; sites would much rather obfuscate the issue than compete on it as a feature.

This essay originally appeared in the Guardian.

Laptop Security while Crossing Borders

schneier — 2009-07-15T12:10:47-0600

Last year, I wrote about the increasing propensity for governments, including the U.S. and Great Britain, to search the contents of people's laptops at customs. What we know is still based on anecdote, as no country has clarified the rules about what their customs officers are and are not allowed to do, and what rights people have.

Companies and individuals have dealt with this problem in several ways, from keeping sensitive data off laptops traveling internationally, to storing the data -- encrypted, of course -- on websites and then downloading it at the destination. I have never liked either solution. I do a lot of work on the road, and need to carry all sorts of data with me all the time. It's a lot of data, and downloading it can take a long time. Also, I like to work on long international flights.

There's another solution, one that works with whole-disk encryption products like PGP Disk (I'm on PGP's advisory board), TrueCrypt, and BitLocker: Encrypt the data to a key you don't know.

It sounds crazy, but stay with me. Caveat: Don't try this at home if you're not very familiar with whatever encryption product you're using. Failure results in a bricked computer. Don't blame me.

Step One: Before you board your plane, add another key to your whole-disk encryption (it'll probably mean adding another "user") -- and make it random. By "random," I mean really random: Pound the keyboard for a while, like a monkey trying to write Shakespeare. Don't make it memorable. Don't even try to memorize it.

Technically, this key doesn't directly encrypt your hard drive. Instead, it encrypts the key that is used to encrypt your hard drive -- that's how the software allows multiple users.

So now there are two different users named with two different keys: the one you normally use, and some random one you just invented.

Step Two: Send that new random key to someone you trust. Make sure the trusted recipient has it, and make sure it works. You won't be able to recover your hard drive without it.

Step Three: Burn, shred, delete or otherwise destroy all copies of that new random key. Forget it. If it was sufficiently random and non-memorable, this should be easy.

Step Four: Board your plane normally and use your computer for the whole flight.

Step Five: Before you land, delete the key you normally use.

At this point, you will not be able to boot your computer. The only key remaining is the one you forgot in Step Three. There's no need to lie to the customs official; you can even show him a copy of this article if he doesn't believe you.

Step Six: When you're safely through customs, get that random key back from your confidant, boot your computer and re-add the key you normally use to access your hard drive.

And that's it.

This is by no means a magic get-through-customs-easily card. Your computer might be impounded, and you might be taken to court and compelled to reveal who has the random key.

But the purpose of this protocol isn't to prevent all that; it's just to deny any possible access to your computer to customs. You might be delayed. You might have your computer seized. (This will cost you any work you did on the flight, but -- honestly -- at that point that's the least of your troubles.) You might be turned back or sent home. But when you're back home, you have access to your corporate management, your personal attorneys, your wits after a good night's sleep, and all the rights you normally have in whatever country you're now in.

This procedure not only protects you against the warrantless search of your data at the border, it also allows you to deny a customs official your data without having to lie or pretend -- which itself is often a crime.

Now the big question: Who should you send that random key to?

Certainly it should be someone you trust, but -- more importantly -- it should be someone with whom you have a privileged relationship. Depending on the laws in your country, this could be your spouse, your attorney, your business partner or your priest. In a larger company, the IT department could institutionalize this as a policy, with the help desk acting as the key holder.

You could also send it to yourself, but be careful. You don't want to e-mail it to your webmail account, because then you'd be lying when you tell the customs official that there is no possible way you can decrypt the drive.

You could put the key on a USB drive and send it to your destination, but there are potential failure modes. It could fail to get there in time to be waiting for your arrival, or it might not get there at all. You could airmail the drive with the key on it to yourself a couple of times, in a couple of different ways, and also fax the key to yourself ... but that's more work than I want to do when I'm traveling.

If you only care about the return trip, you can set it up before you return. Or you can set up an elaborate one-time pad system, with identical lists of keys with you and at home: Destroy each key on the list you have with you as you use it.

Remember that you'll need to have full-disk encryption, using a product such as PGP Disk, TrueCrypt or BitLocker, already installed and enabled to make this work.

I don't think we'll ever get to the point where our computer data is safe when crossing an international border. Even if countries like the U.S. and Britain clarify their rules and institute privacy protections, there will always be other countries that will exercise greater latitude with their authority. And sometimes protecting your data means protecting your data from yourself.

This essay originally appeared on Wired.com.

Data Leakage Through Power Lines

schneier — 2009-07-15T06:17:58-0600

The NSA has known about this for decades:

Security researchers found that poor shielding on some keyboard cables means useful data can be leaked about each character typed.
By analysing the information leaking onto power circuits, the researchers could see what a target was typing.

The attack has been demonstrated to work at a distance of up to 15m, but refinement may mean it could work over much longer distances.

These days, there's lots of open research on side channels.

Poor Man's Steganography

schneier — 2009-07-14T13:48:08-0600

Hide files inside pdf documents: "embed a file in a PDF document and corrupt the reference, thereby effectively making the embedded file invisible to the PDF reader."

Gaze Tracking Software Protecting Privacy

schneier — 2009-07-14T06:20:37-0600

Interesting use of gaze tracking software to protect privacy:

Chameleon uses gaze-tracking software and camera equipment to track an authorized reader's eyes to show only that one person the correct text. After a 15-second calibration period in which the software essentially "learns" the viewer's gaze patterns, anyone looking over that user's shoulder sees dummy text that randomly and constantly changes.
To tap the broader consumer market, Anderson built a more consumer-friendly version called PrivateEye, which can work with a simple Webcam. The software blurs a user's monitor when he or she turns away. It also detects other faces in the background, and a small video screen pops up to alert the user that someone is looking at the screen.

How effective this will mostly be a usability problem, but I like the idea of a system detecting if anyone else is looking at my screen.

SlashDot story.

EDITED TO ADD (7/14): A demo.