Digital Rights Management
We will start our discussion on the applications of cryptography with a seemingly unrelated topic: file-sharing networks. Their popularity over the last five years causes great concern among industries who subsist on the mass distribution of copyrighted digital works. Computers' ability to easily make perfect copies of digital works threatens the very profit model of these industries. One of those affected, the music industry, turned to ingenious "tricks" to implement so-called copy-protection on their CDs. These tricks were at best ineffectual and at worst annoyed paying customers. For viable copy-protection, everyone has turned to cryptography, more specifically, to digital rights management (DRM).
A system of digital rights management is one that controls how a user is allowed to manipulate digital information. Most DRM systems are cryptographic software protocols, although work is being conducted on DRM systems based on the hardware level (we will talk about these later). They work by cryptographically "locking" a file so that only "authorized" users may access, modify, or distribute it.
Proponents of DRM say it is necessary to protect the copyrights of content creators. In reality, DRM aims to do much more than that. An effective DRM system gives the content owners an unlimited ability to control what others can do with their works, even beyond the scope of control traditionally covered by copyright law. By modifying the laws of the digital world, content owners can effectively modify the laws of the real world; they can anoint themselves legislators.
Most legal music download services, Apple's iTunes for example, provide DRM for the content they distribute. Apple's iTunes, one of the more permissive DRM systems, allows you to play a song on only five computers and to burn a playlist to a CD only seven times.
DRM is implemented in movies via the Content Scrambling System for DVDs. Only the DVD Copy Control Association (DVD-CCA) holds the keys for unlocking movies on DVD, so any DVD player must be "sanctioned", otherwise it will not play movies. This causes several restrictions not initially contemplated by traditional copyright law. First is the problem of region encoding. The movie industry has seen fit to "region-encode" a DVD, so that it can only be played by DVD players within that area. If the author, for example, were to go home to Mexico for winter break, his Stanford DVD collection would not work at home and his DVD connection at home would not work at Stanford. Second is the problem of fair use. Copyrights can be legally bypassed for such purposes as academics or parody. Third is the problem of the public domain. When a movie's copyright has expired and it has been released to the public domain, how can we trust the movie industry to release the keys for that movie? If they had a working DRM system they could extend the lifetime of their copyright indefinitely.
The famous example of DRM in documents is Adobe eBooks. Lawrence Lessig famously bought a copy of Lewis Carol's Alice in Wonderland, a book in the public domain, from Adobe in an eBook format. Even though this work is in the public domain and is theoretically free to be used in any way whatsoever, using its DRM Adobe managed to "extend" the effective copyright. Adobe prevented people from using a copy of its digital work without paying for it, distributing it to other people, and above all, strictly forbade people from using the eBook Reader's "Read Aloud" function to read Alice in Wonderland.
For the most part, however, these systems have not worked. DRM systems, Cory Doctorow argues, suffer from a fundamental cryptographic flaw. Let's say Alice makes a creative work P (the plaintext). She wants to sell it to Bob (and the rest of the world), but only if she can be sure her copyrights will be respected. To do so, she chooses a cipher (an encryption scheme) and a secret key, and, taking her plaintext, derives the ciphertext. For Bob to enjoy Alice's creative work, he needs the ciphertext, obviously, but also the cipher and the key. In the case of DRM however, the legitimate user (Bob) is also the attacker (Carol)! Because giving Bob enough information to decode the ciphertext implies giving Carol enough information to decode the ciphertext, Alice is in a bit of a bind.
As a result, several methods for fixing this problem have been suggested, some technical, some not. The technical solution is called the Secure Computing Initiative (SCI). SCI would perform all of the rights-verification at the hardware level, prohibiting you from reading or writing a file if you did not own it or buy permissions for it. The problem with this model is that it does away with the general purpose computer, the Universal Turing Machine (UTM). We would lose the ability to perform certain computations in order to protect the copyrights of others.
The non-technical solution is a law passed by Congress called the Digital Millennium Copyright Act (DMCA). If encryption schemes are locks, the DMCA makes it illegal to pick a lock, make a lock pick, teach someone how to make a lock pick, or tell someone where they can go to learn how to make a lock pick. This law goes beyond the boundary that would have previously defined traditional copyright law, protecting many products and practices that on first intuition should not be copyrighted.
One of the effects of the DMCA has been to limit academic activity on cryptographic systems. Three people have been prevented from speaking publicly about real or perceived weaknesses in DRM systems; they are guilty of teaching someone how they could go about starting to build a lock pick. Edward Felten is a Princeton Professor who was threatened with the DMCA when he tried to present a paper at an academic conference on the cryptographic weaknesses of a proposed music-protection scheme. His paper is still unpublished. Dmitry Skylarov is a Russian programmer working for a Russian company, Elcomsoft, which makes software for recovering Adobe PDFs which had been locked but whose password had been forgotten. This same program can defeat the copy-protection on eBooks, which is based on the same technique. The work Dmitry performed and sold in Russia was perfectly legal in Russia, but when he came to the United States to give a conference, he was arrested by the FBI on charges of having violated the DMCA. The third example is Niels Fergusen, a Dutch cryptography expert who discovered a flaw in Intel's security protocol, but who has refused to publish a paper on it for fear of being prosecuted under the DMCA.
Another effect of the DMCA is that is greatly widens the scope of traditional copyright law. Manufacturers of car engines, print cartridges, and even garage-door openers, all products with firmware in them, have threatened with the DMCA to prevent people from tinkering with their products. The lay person, however, would not consider a garage-door opener to be a copyrighted work.
This leads us to what I call Lessig's Insight: computer code can be more powerful than any law code. Lawrence Lessig, a Professor at Stanford's Law School, has no technical training, but he understands the power of computers. He realizes that the rules to our world will largely be built into these mysterious digital machines and that, if we are not careful, we could lose some of the rights we have come to appreciate. As a society, we have realized the important influence that laws have on our lives, and so have developed very careful and complicated systems to choose our lawmakers. However, we have no similar system for choosing what laws are written into the computer code of the digital world and for who gets to write them.
That said, cryptography also allows for many new and exciting frontiers to be explored. Things like electronic voting, near-perfect privacy, and anonymous digital cash become possible with advanced cryptographic techniques. These and other things could bring great benefit, or great harm, to society.