February 28, 2017

Archives for September 2010

Advice for New Graduate Students

[Ed Felten says: This is the time of year when professors offer advice to new students. My colleague Prof. Jennifer Rexford gave a great talk to a group of our incoming engineering Ph.D. students, about how to make the most of graduate school. Here’s what she said: ]

Those of you who know me, know that I collect quotations as a hobby. (The short version of the story is that I moved around a lot as a kid. Quotations are small and very portable, making them a good hobby.) Anyway, two eminent scientists, Albert Einstein and Lewis Thomas, who were at Princeton the 1930s both have something interesting (and seemingly contradictory) to say about the role of the individual:

Albert Einstein (physics): “All that is valuable in human society depends upon the opportunity for development accorded the individual.”

Lewis Thomas (medicine, biology, Princeton class of ’33): “There is really no such creature as a single individual; he has no more life of his own than a cast-off cell marooned from the surface of your skin.”

These two quotations embody so much of what graduate school is all about.

Individual Development

First, graduate school is a highly individual experience. Compared to the somewhat anonymous experience of college — where you sit in large classes, do the same homeworks, and take the same tests with many other students — graduate school is a highly personal. Nobody else is doing quite the same research you are doing (or at least you hope they are not), and you get direct (sometimes pointed) feedback on your individual work — from your advisor, from your peers, and from reviewers of the papers you submit and the talks you give. And when your work is good but not great, you don’t just take the A- and move on to the next assignment — you keep plugging away and get more feedback and, eventually, you nail it. This is an amazingly efficient way to learn, grow, and create great scholarship.

Yet, there is a downside. The critique of your work, however well-meaning and “good for you,” will sometimes feel relentless. It requires some toughening of the skin, and a delicate little dance to simultaneously be in love with your work (so you have the tenacity you need to always dig deeper) and yet have enough emotional distance to be able to take constructive criticism of how your work looks in its early stages. It’s not an easy balance to strike, and I’m sure all of us who do research still struggle with it. I know I do. This is one of the many ways in which grad school is as much as emotional challenge as it is an intellectual one.

Another important aspect of the “individual” in graduate school is to learn your research “taste.” You may not know it yet, but you are weird. You come to research problems with some peculiar sensibility that nobody else has. You are attracted to a certain kind of research problem — maybe a messy practical problem, or a sharply formulated (but very hard) theoretical problem, or something in between. You notice a certain kind of weakness or gap in other people’s research. You have a particular set of techniques or approaches to solving problems. Graduate school is a wonderful time to figure out what your “taste” is, so you can craft your own agenda for the technical problems you pursue in the years ahead.

So, then, graduate school really is the epitome of what Einstein called the “development of the individual.” And I hope during your time here, you get the kind of opportunities for individual development that you deserve. Experiences that will let you produce deeper scholarship that expands the base of knowledge in your fields, and become more accomplished at conveying new and sometimes complex ideas to others.

Part of a Group

Yet, for all of my blathering on about the individual, graduate school is also a collective experience. You are part of a research group, a department, a discipline, (for many of you) an engineering school, a graduate school, and student groups like GWISE.

I want to say a few words about your research group, because it is so important. Your officemates, and the other graduate students around you, are such an important part of your graduate school experience. Not only do they provide a sense of community, and a community that truly understands your experiences, though that is certainly important. But they also mentor you on topics small and large.

I had a great officemate, Jim, in graduate school. He took ten years to graduate, and had already been there seven years when I arrived. So, Jim knew everything about everything. He taught me an important lesson I value to this day — how to be efficient. He would sit at the next desk and admonishingly say, “Jen, I hear the sounds of repetitive keystrokes. Today you will learn Perl.” To be honest, it was kind of creepy at first, but Jim would watch out for me out of the corner of his eye. He taught me things that would save me time, leaving me with the time and energy I needed to tackle bigger and more interesting problems.

Your classmates will also provide wonderful moments of professional serendipity, random encounters over coffee or foosball that make you aware of a body of work you didn’t know about, or recognize a previously unappreciated connection between two disciplines. You may even become the match-maker for the faculty, bringing two professors together to collaborate because you see a connection in their research that they were unable to see. The chance encounters, the candid feedback on your research, the unplanned discussions about research taste and philosophy — these are all a great part of interacting with your group mates.

I must caution you, though, about an important enemy against this kind of informal interactions. The Internet. Okay, so my research focuses on the Internet, so it may seem strange for me to be so negative about it, but this is important so I’ll make an exception. The Internet makes it far too easy to work from home, or a cafe, or on the train, rather than in your office or lab with your peers. Your choice to work away from the office is, in fact, perfectly rational. Coming into the office has a defined cost, in terms of your time and (perhaps) having to get out of your pajamas and take a shower. And, all of this is in exchange for some vague, speculative benefit — that you might have a chance encounter that truly changes your research. And, frankly, in any one day, you probably won’t have a profound experience in your office, and your officemates may not even be in the same scholarly mood as you. But, I entreat you to go anyway.

And, I encourage you to have a broader sense of community with each other, whether in your departments, or the school of engineering, or in groups like this one. Not only for the professional serendipity — though that will happen. But for the friendship and support. Graduate school is fun but it is also hard, and sometimes frustrating, and having some balance in your life will make the whole experience more worthwhile.

In fact, for what it’s worth, I find the students in my group who are more engaged with other students and student groups often graduate sooner than the other students. They often are better at managing their time, working intensely and efficiently to leave space in their lives for their other pursuits. And, they are more comfortable reaching out to other students for help, whether for feedback on a paper or guidance on an analytical technique or a software tool. They know more about the peculiarities of the faculty, and how to work around them. And, for the students who are not native English speakers, the social interactions also have a side benefit of sharpening their English skills. Mastering a language is, frankly, pretty boring work. Socializing in English is a much more enjoyable way to learn the language than any formal study could ever be.

So, in closing, I do think that graduate school is an unusual experience, both highly individual (in your training and professional development) and highly collective (in how you are part of a research group, a discipline, and a larger community). I hope you find both aspects of your time here at Princeton rewarding, and that you also make time to give back to the next group of students who arrive at Princeton after you.

Copyright, Censorship, and Domain Name Blacklists at Home in the U.S.

Last week, The New York Times reported that Russian police were using copyright allegations to raid political dissidents, confiscating the computers of advocacy groups and opposition newspapers “under the pretext of searching for pirated Microsoft software.” Admirably, Microsoft responded the next day with a declaration of license amnesty to all NGOs:

To prevent non-government organizations from falling victim to nefarious actions taken in the guise of anti-piracy enforcement, Microsoft will create a new unilateral software license for NGOs that will ensure they have free, legal copies of our products.

Microsoft’s authorization undercuts any claim that its software is being infringed, but the Russian authorities may well find other popular software to use as pretext to disrupt political opponents.

“Piracy” has become the new tax evasion, an all-purpose charge that can be lobbed against just about anyone. If the charge alone can prompt investigation — and any electronics could harbor infringing copies — it gives authorities great discretion to interfere with dissidents.

That tinge of censorship should raise grave concern here in the United States, where Patrick Leahy and Orrin Hatch, with Senate colleagues, have introduced the “Combating Online Infringement and Counterfeits Act.” (PDF).

This Bill would give the Attorney General the power to blacklist domain names of sites “offering or providing access to” unauthorized copyrighted works “in complete or substantially complete form, by any means, including by means of download, transmission, or otherwise, including the provision of a link or aggregated links to other sites or Internet resources for obtaining such copies for accessing such performance or displays”; as well as those offering items with counterfeit trademarks. The AG could obtain court orders, through “in rem” proceedings against the domains, enjoining the domain name registrars or registries from resolving the names. Moreover, in the case of domains without a U.S. registrar or registry, other service providers, financial transaction providers, and even advertising servers could be caught in the injunctive net.

While the Bill makes a nod to transparency by requiring publication of all affected domain names, including those the Department of Justice “determines are dedicated to infringing activities but for which the Attorney General has not filed an action under this section,” it then turns that information site into a invitation to self-censorship, giving legal immunity to all who choose to block even those names whose uses’ alleged illegality has not been tested in court. (Someone who is listed must petition, under procedures to be determined by the AG, to have names removed from the list.)

Finally, the statute’s warped view — that allegations of infringement can only be good — is evident in the public inputs it anticipates. The public and intellectual property holders shall be invited to provide information about “Internet sites that are dedicated to infringing activities,” but there is no provision for the public to complain of erroneous blockage or lawful sites mistakenly or maliciously included in the blacklist.

Hollywood likes the Bill. Unfortunately, there’s plenty of reason to believe that allegations of infringement will be misused here in the United States. Even those who oppose infringement of copyright and trademark (myself included) should oppose this censorious attempt to stop it.

cross-posted at Legal Tags.

Understanding the HDCP Master Key Leak

On Monday, somebody posted online an array of numbers which purports to be the secret master key used by HDCP, a video encryption standard used in consumer electronics devices such as DVD players and TVs. I don’t know if the key is genuine, but let’s assume for the sake of discussion that it is. What does the leak imply for HDCP’s security? And what does the leak mean for the industry, and for consumers?

HDCP is used to protect high-def digital video signals “on the wire,” for example on the cable connecting your DVD player to your TV. HDCP is supposed to do two things: it encrypts the content so that it can’t be captured off the wire, and it allows each endpoint to verify that the other endpoint is an HDCP-licensed device. From a security standpoint, the key step in HDCP is the initial handshake, which establishes a shared secret key that will be used to encrypt communications between the two devices, and at the same time allows each device to verify that the other one is licensed.

As usual when crypto is involved, the starting point for understanding the system’s design is to think about the secret keys: how many there are, who knows them, and how they are used. HDCP has a single master key, which is supposed to be known only by the central HDCP authority. Each device has a public key, which isn’t a secret, and a private key, which only that device is supposed to know. There is a special key generation algorithm (“keygen” for short) that is used to generate private keys. Keygen uses the secret master key and a public key, to generate the unique private key that corresponds to that public key. Because keygen uses the secret master key, only the central authority can do keygen.

Each HDCP device (e.g., a DVD player) has baked into it a public key and the corresponding private key. To get those keys, the device’s manufacturer needs the help of the central authority, because only the central authority can do keygen to determine the device’s private key.

Now suppose that two devices, which we’ll call A and B, want to do a handshake. A sends its public key to B, and vice versa. Then each party combines its own private key with the other party’s public key, to get a shared secret key. This shared key is supposed to be secret—i.e., known only to A and B—because making the shared key requires having either A’s private key or B’s private key.

Note that A and B actually did different computations to get the shared secret. A combined A’s private key with B’s public key, while B combined B’s private key with A’s public key. If A and B did different computations, how do we know they ended up with the same value? The short answer is: because of the special mathematical properties of keygen. And the security of the scheme depends on this: if you have a private key that was made using keygen, then the HDCP handshake will “work” for you, in the sense that you’ll end up getting the same shared key as the party on the other end. But if you tried to use a random “private key” that you cooked up on your own, then the handshake won’t work: you’ll end up with a different shared key than the other device, so you won’t be able to talk to that device.

Now we can understand the implications of the master key leaking. Anyone who knows the master key can do keygen, so the leak allows everyone to do keygen. And this destroys both of the security properties that HDCP is supposed to provide. HDCP encryption is no longer effective because an eavesdropper who sees the initial handshake can use keygen to determine the parties’ private keys, thereby allowing the eavesdropper to determine the encryption key that protects the communication. HDCP no longer guarantees that participating devices are licensed, because a maker of unlicensed devices can use keygen to create mathematically correct public/private key pairs. In short, HDCP is now a dead letter, as far as security is concerned.

(It has been a dead letter, from a theoretical standpoint, for nearly a decade. A 2001 paper by Crosby et al. explained how the master secret could be reconstructed given a modest number of public/private key pairs. What Crosby predicted—a total defeat of HDCP—has now apparently come to pass.)

The impact of HDCP’s failure on consumers will probably be minor. The main practical effect of HDCP has been to create one more way in which your electronics could fail to work properly with your TV. This is unlikely to change. Mainstream electronics makers will probably continue to take HDCP licenses and to use HDCP as they are now. There might be some differences at the margin, where manufacturers feel they can take a few more liberties to make things work for their customers. HDCP has been less a security system than a tool for shaping the consumer electronics market, and that is unlikely to change.