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RFID, Present and Future

October 26, 2005 by

One of the advantages of teaching in a good university is the opportunity to hear smart students talk to each other about complicated topics. This semester I’m teaching a graduate seminar in technology and privacy, to a group of about ten computer science and electrical engineering students. On Monday the class discussed the future of RFID technology.

The standard scenario for RFID involves affixing a small RFID “tag” to a consumer product, such as an item of clothing sold at WalMart. (I’m using WalMart as a handy example here; anyone can use RFID.) Each tag has a unique ID number. An RFID “reader” can use radio signals to determine the ID numbers of any tags that are nearby. WalMart might use an RFID reader to take an inventory of which items are in their store, or which items are in the shopping cart of a customer. This has obvious advantages in streamlining inventory control, which helps WalMart operate more efficiently and sell products at lower prices.

This sounds fine so far, but there is a well-known problem with this scheme. When a customer buys the item and takes it home, the RFID tag is still there, so people may be able to track the customer or learn what he is carrying in his backpack, by scanning him and his possessions for RFID tags. This scares many people.

The risk of post-sale misuse of RFID tags can be mitigated by having WalMart deactivate or “kill” the tags when the customer buys the tag-containing item. This could be done by sending a special radio code to the tag. On receiving the kill code, the tag would stop operating. (Any practical kill feature would allow a special scanner to detect that a dead tag was present, but not to learn the dead tag’s ID number.)

Killing tags is a fine idea, but perhaps the consumer wants to use the tag for his own purposes. It would be cool if my laundry hamper knew which clothes were in it and could warn me of an impending clean-sock crisis, or if my fridge knew whether it contained any milk and how long that milk had been present. These things are possible if my clothing and food containers have working RFID tags.

One way to get what we want is to have smarter tags that use cryptography to avoid leaking information to outsiders. A smart tag would know the cryptographic key of its owner, and would only respond to requests properly signed by that key; and it would reveal its ID number in such a way that only its owner could understand it. At the checkout stand, WalMart would transfer cryptographic ownership of a tag to the buyer, rather than killing the tag. Any good cryptographer can figure out how to make this work.

The problem at present is that garden-variety RFID tags can’t do fancy crypto. Tags don’t have their own power source but get their power parasitically from an electromagnetic “carrier wave” broadcast by the reader. This means that the tag has a very limited power budget and very limited time – not nearly enough of either to do serious crypto. Some people argue that the RFID privacy problem is an artifact of these limitations of today’s RFID tags.

If so, that’s good news, because Moore’s Law is increasing the amount of computing we can do with a fixed power or time budget. If Moore’s Law applies to RFID circuits – and it seems that it should – then the time will come in a few years when dirt-cheap RFID tags can do fancy crypto, and therefore can be more privacy-friendly than they are today. The price difference between simple tags and smart tags will be driven toward zero by Moore’s Law, so there won’t be a cost justification for using simpler but less privacy-friendly tags.

But here’s the interesting question: when nicer RFID tags become possible, will people switch over to using them, or will they keep using today’s readable-by-everybody tags? If there’s no real cost difference, there are only two reasons we might not switch. The first is that we are somehow locked in by backward compatibility, so that any switch to a new technology incurs costs that nobody wants to be the first to pay. The second is a kind of social inertia, in which people are so accustomed to accepting the privacy risks of dumber RFID technologies that they don’t insist on improvement. Either of these scenarios could develop, and if they do, we may be locked out from a better technology for quite a while.

Our best hope, perhaps, is that WalMart can benefit from a stronger technology. Current systems are subject to various uses that WalMart may not like. For example, a competitor might use RFID to learn how many of each product WalMart is stocking, or to learn where WalMart customers live. Or a malicious customer might try to kill or impersonate a WalMart tag. Smarter RFID tags can prevent these attacks. Perhaps that will be enough to get WalMart to switch.

Looking further into the future, the privacy implications of small, communicating devices will only get more serious. The seminar read a paper on “smart dust”, a more futuristic technology involving tiny, computationally sophisticated motes that might some day be scattered across an area, then picked up by passersby, as any dust mote might be. This is a really scary technology, if it’s used for evil.

Today, inventory control and remote tracking come in a single technology called RFID. Tomorrow, they can be separated, so that we can have the benefits of inventory control (for businesses and individuals) without having to subject ourselves to tracking. Tracking will be more possible than ever before, but at least we won’t have to accept tracking as a side-effect of shopping.

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Do University Honor Codes Work?

October 25, 2005 by

Rick Garnett over at ProfsBlawg asked his readers about student honor codes and whether they work. His readers, who seem to be mostly lawyers and law students, chimed in with quite a few comments, most of them negative.

I have dealt with honor codes at two institutions. My undergraduate institution, Caltech, has a simply stated and all-encompassing honor code that is enforced entirely by the students. My sense was that it worked very well when I was there. (I assume it still does.) Caltech has a small (800 students) and relatively homogeneous student body, with a student culture that features less student versus student competitiveness than you might expect. Competition there tends to be student versus crushing workload. The honor code was part of the social contract among students, and everybody appreciated the benefits it provided. For example, you could take your final exams at the time and place of your choosing, even if they were closed-book and had a time limit; you were trusted to follow the rules.

Contrasting this to the reports of Garnett’s readers, I can’t help but wonder if honor codes are especially problematic in law schools. There is reportedly more cutthroat competition between law students, which could be more conducive to ethical corner-cutting. Competitiveness is an engine of our adversarial legal system, so it’s not surprising to see law students so eager to win every point, though it is disappointing if they do so by cheating.

I’ve also seen Princeton’s disciplinary system as a faculty member. Princeton has a student-run honor code system, but it applies only to in-class exams. I don’t have any first-hand experience with this system, but I haven’t heard many complaints. I like the system, since it saves me from the unpleasant and trust-destroying task of policing in-class exams. Instead, I just hand out the exams, then leave the room and wait nearby to answer questions.

Several years ago, I did a three-year term on Princeton’s Student-Faculty Committee on Discipline, which deals with all serious disciplinary infractions, whether academic or non-academic, except those relating to in-class exams. This was hard work. We didn’t hear a huge number of cases, but it took surprisingly long to adjudicate even seemingly simple cases. I thought this committee did its job very well.

One interesting aspect of this committee was that faculty and students worked side by side. I was curious to see any differences between student and faculty attitudes toward the disciplinary process, but it turned out there were surprisingly few. If anything, the students were on average slightly more inclined to impose stronger penalties than the faculty, though the differences were small and opinions shifted from case to case. I don’t think this reflected selection bias either; discussions with other students over the years have convinced me that students support serious and uniform punishment for violators. So I don’t think there will be much difference in the outcomes of a student-run versus a faculty-run disciplinary process.

One lesson from Garnett’s comments is that an honor code will die if students decide that enforcement is weak or biased. Here the secrecy of disciplinary processes, which is of course necessary to protect the accused, can be harmful. Rumors do circulate. Sometimes they’re inaccurate but can’t be corrected without breaching secrecy. For example, when I was on Princeton’s discipline committee, some students believed that star athletes or students with famous relatives would be let off easier. This was untrue, but the evidence to contradict it was all secret.

Academic discipline seems to have a major feedback loop. If students believe that the secret disciplinary processes are generally fair and stringent, they will be happy with the process and will tend to follow the rules. This leaves the formal disciplinary process to deal with the exceptions, which a good process will be able to handle. Students will buy in to the premise of the system, and most people will be happy.

If, on the other hand, students lose their trust in the fairness of the system, either because of false rumors or because the system is actually unfair, then they’ll lose their aversion to rule-breaking and the system, whether honor-based or not, will break down. Several of Garnett’s readers tell a story like this.

One has to wonder whether it makes much difference in practice whether a system is formally honor-based or not. Either way, students have an ethical duty to follow the rules. Either way, violations will be punished if they come to light. Either way, at least a few students will cheat without getting caught. The real difference is whether the institution conspicuously trusts the students to comply with the rules, or whether it instead conspicuously polices compliance. Conspicuous trust is more pleasant for everybody, if it works.

[Feel free to talk about your own experiences in the comments. I’m especially eager to hear from current or past Princeton students.]

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Breathalyzers and Open Source

October 21, 2005 by

Lawyers for 150 Floridians accused of drunk driving have asked a court to order the disclosure of the source code for software running in the breathalyzer machines used by police to analyze their blood alcohol level, according to a Tom Sanders story on vunet.

The defendants say they have the right to examine the machines that accused them, and that a meaningful examination requires access to the machines’ software. Prosecutors say the code is a trade secret.

The accused are right that one needs the code to understand fully how the machines work. The machines consist of sensors, a user interface, and control software. The software is the “brain” of the machine, and it is almost certainly involved in the calculations that derive a blood alcohol value from the sensor readings, as well as the display of the calculated value. If the accused have the right to fully examine the machines – and the article says that they do under Florida law – then they should see the source code.

Contrary to the article and some other commentators, this is not a dispute over whether the software should be open source. The accused aren’t seeking to open the software to everybody; they only want it opened to their legal teams.

There are standard practices for handling trade-secret information that must be turned over in court cases. A court will typically establish a protective order, which is a kind of nondisclosure agreement covering secret material that is turned over by one side to the other. The protective order will require parties to keep the information secret and to use it only for purposes related to the court proceedings. Typically the information can be turned over to a limited number of expert analysts who have also signed the protective order. Documents containing secret information are filed under seal, and testimony about secret matters may take place in a closed courtroom.

So this issue is not about open source, but about ensuring fairness for the accused. If they’re going to be accused based on what some machine says, then they ought to be allowed to challenge the accuracy of the machine. And they can’t do that unless they’re allowed to know how the machine works.

You might argue that the machine’s technical manuals convey enough information. Having read many manuals and examined the innards of many software systems, I’m skeptical of such claims. Often, knowing how the maker says a machine works is a poor substitute for knowing how it actually works. If a machine is flawed, it’s likely the maker will either (a) not know about the flaw or (b) be unwilling to admit it exists.

If the article’s description of Florida law is correct, this seems like a pretty easy decision for the court.

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Mossberg Takes on DRM, Urges CD-DRM Boycott

October 20, 2005 by

Walt Mossberg, whose Personal Technology column in the Wall Street is a must-read for many influential but non-geeky technology enthusiasts, discusses the DRM issue in today’s column. No much in the column will be new to regular readers here, or to anyone immersed in the digital copyright issue. But of course Mossberg writes for a different audience, and the column serves that audience well by explaining the issues clearly and maintaining a moderate tone.

In my view, both sides have a point, but the real issue isn’t DRM itself – it’s the manner in which DRM is used by copyright holders. Companies have a right to protect their property, and DRM is one means to do so. But treating all consumers as potential criminals by using DRM to overly limit their activities is just plain wrong.

Let’s be clear: The theft of intellectual property on the Internet is a real problem. Millions of copies of songs, TV shows and movies are being distributed over the Internet by people who have no legal right to do so, robbing media companies and artists of rightful compensation for their work.

Even if you think the record labels and movie studios are stupid and greedy, as many do, that doesn’t entitle you to steal their products. If your local supermarket were run by people you didn’t like, and charged more than you thought was fair, you wouldn’t be entitled to shoplift Cheerios from its shelves.

On the other hand, I believe that consumers should have broad leeway to use legally purchased music and video for personal, noncommercial purposes in any way they want – as long as they don’t engage in mass distribution. They should be able to copy it to as many personal digital devices as they own, convert it to any format those devices require, and play it in whatever locations, at whatever times, they choose.

Mossberg urges music and movie companies to use DRM to limit large-scale pirates, while giving ordinary users wide leeway for personal use.

Instead of using DRM to stop some individual from copying a song to give to her brother, the industry should be focusing on ways to use DRM to stop the serious pirates – people who upload massive quantities of music and videos to so-called file-sharing sites, or factories in China that churn out millions of pirate CDs and DVDs.

This is a nice vision, but it’s not really possible. It’s abundantly clear by now that no DRM system can stop serious pirates. A DRM system that stops serious pirates, and simultaneously gives broad leeway to ordinary users, is even harder to imagine. It’s not going to happen.

Although he doesn’t address it directly, Mossberg implicitly rejects the other argument for DRM, which says that DRM can enable new pricing models for content and can therefore foster market efficiency. Mossberg says flatly that consumers should have a broad right to make personal uses of content they have bought.

The most surprising part of the column – remember that this is in the Wall Street Journal – is Mossberg’s call for a boycott of products with restrictive DRM, such as copy-protected CDs.

Until then, I suggest that consumers avoid stealing music and videos, but also boycott products like copy-protected CDs that overly limit usage and treat everyone like a criminal. That would send the industry a message to use DRM more judiciously.

Whether it’s a flat boycott, or just a disinclination to buy such products, this would have an impact on the industry’s DRM choices.

To make it happen, people need to learn which CDs use DRM and which don’t. One way to tell on CDs is to look for the official CD logo on the package. If the CD logo is missing, the disc probably doesn’t comply with the CD standard, and the noncompliance is probably caused by DRM. Alternatively, somebody could set up a website with information about which discs used DRM. It would be nice, too, to have a site with information about DVDs, to keep track, for instance, of which discs force viewers to watch movie previews before seeing the movie they bought.

It can’t be too hard to set up such a site. If you put ads on it, you could probably make a profit. Who wants to build it?

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EFF Researchers Decode Hidden Codes in Printer Output

October 18, 2005 by

Researchers at the EFF have apparently confirmed that certain color printers put hidden marks in the pages they print, and they have decoded the marks for at least one printer model.

The marks from Xerox DocuColor printers are encoded in an array of very small yellow dots that appear all over the page. The dots encode the date and time when the page was printed, along with what appears to be a serial number for the printer. You can spot the dots with blue light and a 10X magnifier, and you can then decode the dots to get the date, time, and serial number.

Many other printers appear to do something similar; the EFF has a list.

The privacy implications are obvious. It’s now possible to tell when a document was printed, and when two documents were printed on the same printer. It’s also possible, given a document and a printer, to tell whether the document was printed on that printer.

Apparently, this was done at direction of the U.S. government.

The U.S. Secret Service admitted that the tracking information is part of a deal struck with selected color laser printer manufacturers, ostensibly to identify counterfeiters. However, the nature of the private information encoded in each document was not previously known.

…

Xerox previously admitted that it provided these tracking dots to the government, but indicated that only the Secret Service had the ability to read the code.

The assertion that only the Secret Service can read the code is false. The code is quite straightforward. For example, there is one byte for (the last two digits of) the year, one byte for the month, one byte for the day, one byte for the hour, and one byte for the minute.

Now that the code is known, it should be possible to forge the marks. For example, I could cook up an array of little yellow dots that encode any date, time, and serial number I like. Then I could add the dots to any image I like, and print out the image-plus-dots on a printer that doesn’t make the marks. The resulting printout would have genuine-looking marks that contain whatever information I chose.

This could have been prevented by using cryptography, to make marks that can only be decoded by the Secret Service, and that don’t allow anyone but the secret service to detect whether two documents came from the same printer. This would have added some complexity to the scheme, but that seems like a good tradeoff in a system that was supposed to stay secret for a while.

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