Steve,
could you offer a precis on what Henry said, assuming it is reducible to relatively lay terms?
This paper explains the security issues and strategy much better than anything I could offer:
ebooknet.com
Cryptography for Copyright Enforcement
Martin F. Eberhard
Posted Fri Mar 24, '00
In February -- almost a month before the disclosure that hackers had decrypted a version of Stephen King's new eBook -- NuvoMedia cofounder and CEO Martin Eberhard finished this white paper on the importance of a "closed environment" for reliable eBook encryption. The paper argues that any reading system where decrypted content and the decryption key exist on the same machine -- or where pirating software can run alongside the system -- is vulnerable to hacker attacks.
February 22, 2000
Books are beginning to follow music into the brave new world of electronic distribution. Fortunately, book publishers can learn from the music industry's expensive mistake of taking copyright enforcement lightly. Almost every electronic book distribution system today has cryptography at the center of its copyright enforcement strategy, intended to prevent loss of revenue due to piracy. But are all these systems really secure?
Many claims have been made about the suitability of computer cryptography for enforcing copyrights. Proponents of various copyright enforcement mechanisms talk about the strength of cryptographic algorithms with names like RSA, ElGamel, Diffie-Hellman and Blowfish, with seemingly large key sizes that should take years or decades to crack using sophisticated equipment. And yet, we regularly read about major copyright piracy disasters, such as demonstrated in the music CD and the DVD video industries. Why is this, and how can we prevent disasters like these in the book industry?
Copyright Violation
To begin with, let's separate copyright violators into two camps. In the first camp we find the determined computer hacker. This person has considerable skill and technology at his command. He knows that what he is doing is wrong but is none the less willing to spend time and resources to break through a security system. The determined hacker is motivated by a variety of forces, the most common of which is simply the mischievous fun of hacking someone else's security. He may use pirated copies for his own purposes or he may distribute them (most easily on the Internet) -- for fun or for profit. Or, the hacker might create a piracy software program that others can easily use to create copies. Note that bound paper books don't prevent a person as intent as the determined hacker from making pirated paper copies.
In the second camp we find the casual copier -- who paradoxically poses a greater threat to publishers than determined hacker does. The casual copier is not willing to spend much time or resources creating pirated copies and indeed does not really consider his occasional copying to be wrong. He will create copies if it is easy and give these copies to friends. He will use copies from friends or copies found on the Internet. He will also use readily available piracy software if it is easy to download and use. But it is this casual copier who will cause "viral distribution" of pirated copies -- each person passing copies on to a few friends, who in turn pass them on to a few more, until thousands or millions of pirated copies exist. Note that the bound paper book provides perfectly adequate protection against this kind of copying -- because it is difficult and time consuming to copy a bound book and because a photocopy of a book is of much lower quality than a bound book.
Copyright Enforcement
There are two basic approaches to enforcing copyrights. The first is a legal approach: we can keep an eye out for pirated copies -- particularly for Internet sites that distribute pirated copies -- and, if possible, sue the people involved. Various techniques (such as watermarking) that help to identify the source of the pirated copies help with legal enforcement. Legal enforcement works for shutting down big operators such as web sites that distribute pirated copies. But it cannot stop widespread viral distribution of pirated copies -- it just isn't practical to sue every college student in every dorm room across the country.
The second approach to copyright enforcement is a technical one: we make it sufficiently difficult to create copies that the casual copier will not bother. Today, this typically involves cryptography and the use of adequately closed systems, as well as other security measures. However, it must be recognized that any technical approach for copyright enforcement will not prevent the determined hacker from eventually hacking through the system; only legal methods can prevent the hacker from distributing pirated copies. But importantly, the technical copyright enforcement system used must prevent casual copiers from loading and using piracy software developed by expert hackers.
Cryptography Requirements
It is important to understand that cryptography was not invented to prevent copying -- it was invented to keep messages secret during transmission: a submarine radios a message to a battleship, and the enemy must not be able to read the intercepted message. In this scenario, both the sender and the receiver are trusted -- once the receiver has decrypted the message, the cryptography's job is done.
For copyright protection, the situation is very different: it is the receiver of the message who is not trusted. Rather than keeping the message secret, the purpose of cryptography is to prevent the receiving party from copying the message even after it is decrypted. (Generally speaking, the contents of the message are not even secret -- the book's title is known; anyone can find the contents at a library or bookstore.)
Since we are using cryptography differently than its original purpose, there are different requirements for its success. To prevent widespread, viral distribution of pirated copies, a cryptography-based copyright enforcement system must meet the following three criteria:
1. Strong cryptography must be used. The cryptographic algorithm must be strong enough to remain difficult to break -- even many years in the future. Fortunately, since computer cryptography was invented to keep military secrets, any reasonably strong cryptographic algorithm is enough.
2. Decryption must occur only in a secure environment. A secure environment is a closed system where copying is prevented and -- importantly -- it is impossible to load any software that could be used to create copies. Note that while it may be possible to create a system for reading books on a PC that blocks copying, the very nature of a PC allows other software to also be loaded -- in this case, piracy software designed to circumvent the reading-system's security.
3. Encryption must be done uniquely for each user. If the same encryption key is used for all books, then books can be passed around. But much worse, a hacker could create a "master key" program that unlocks every single encrypted book.
Example: Music CD's and CD Rippers
The inventors of music CDs did not anticipate that computers would have CD drives and software for reading music CDs. Also, a ten-megabyte hard disk was considered to be quite large at the time, so the sheer size of a 600-megabyte CD made copying one unmanageable. For these reasons, the only copyright enforcement mechanism on a music CD is the inherent difficulty of getting the data off of the CD. Unfortunately for the music industry, practically every PC now comes with a CD reader and a multi-gigabyte hard disk, and many even sport a CD writer. Worse, there are now many easy-to-use programs (called "CD Rippers") that allow anyone to easily create perfect digital copies of music CDs. Today, every major music label is reporting significant decreases in revenue that they attribute solely to piracy (1). Indeed, the college dorm-room stereo system of yesterday has been replaced by a sound system attached to the student's PC -- with a hard disk full of music gleaned from the Internet. Music CDs should have used strong cryptography.
Example: Microsoft's Windows Media Audio
The widespread sharing of music on the Internet has created demand for a secure system that would allow music to be distributed electronically, but which would prevent music piracy. In August 1999, Microsoft released "Windows Media Audio" to meet this demand. Unfortunately, only one day after it was released, at least two easy-to-use hacking programs were already available for free on the web (2). Indeed, today, there are many such hacking programs that can easily pirate music from every single allegedly secure PC-based music system. Most of these programs take advantage of the unavoidable fact that the music must ultimately be decrypted on the PC so that it may be enjoyed. The trouble is that both the decryption keys and the decrypted music itself must at some time exist in the PC and can therefore be copied by a piracy program that is also running on the PC. For this reason, it is fundamentally impossible to prevent the creation and distribution of push-button piracy software that runs on a PC -- or any other open-system machine such as a Mac or a Palm Pilot. Copyrighted material should only be decrypted in a secure environment.
Example: DVD Movies
Mass production required that Digital Video Disks (DVDs) be encrypted with a limited number of keys. Unfortunately, after the motion picture industry spent years negotiating the encryption standard for digital videodisks, a small group of Norwegian hackers recently released a program (called DeCSS) that can break the encryption on almost any DVD (3). DeCSS is basically a master key for the cryptography used on DVDs that can be downloaded for free from the Internet and operated by a casual user. (The only thing preventing widespread piracy of DVD movies now is the sheer size of a DVD movie -- but the example of the music CD teaches us that this won't be a limitation for long.) Encryption must be done uniquely for each customer.
A Secure Distribution System
As these examples show, any copyright enforcement system that does not meet all three criteria is subject to widespread piracy. NuvoMedia designed the Rocket eBook and the Rocket System as a secure distribution system that meets these criteria and is therefore immune to widespread piracy by casual users. Here's how it works:
When a customer buys a book to read on her Rocket eBook (a RocketEdition), it is uniquely encrypted -- at the moment of purchase -- for her Rocket eBook (with a strong 768-bit ElGamel asymmetric encryption algorithm.) It is delivered over the Internet in its encrypted form to her PC, where it is captured and stored while still encrypted. There is no opportunity for piracy programs like those used to crack the "secure" music distribution systems, since the book is never decrypted on her PC, and the keys necessary to decrypt it never exist on her PC.
When she wants to read her new RocketEdition, she loads the (still encrypted) file into her Rocket eBook. The Rocket eBook itself is a secure environment: copying is not allowed, and it is not possible for a casual user to load any unauthorized software (particularly hacking software) into it. The RocketEdition is only decrypted for reading within this secure environment and can never leave the Rocket eBook. For added security, the RocketEdition even remains encrypted within the Rocket eBook's storage ? only the page currently being read is ever decrypted.
If a determined hacker with access to sophisticated equipment took apart his own Rocket eBook and somehow got the decryption keys out, he would be able to decrypt only the titles that he has purchased. If he tried to create a "master key" program like DeCSS, it would not work for anyone else's RocketEditions, since everyone's RocketEditions are encrypted with unique keys for their Rocket eBooks. Thus, even a breach of security by a determined hacker would not lead to widespread distribution of piracy software and pirated copies, such as is happening with DVDs.
Cryptography's Place
Cryptography is an important part of any copyright enforcement system for eBooks, though cryptography alone is not enough. Although cryptography cannot prevent the determined efforts of an expert hacker, it can prevent widespread casual copying, provided that casual users cannot load and use piracy software created by experts. This requires that in addition to strong cryptography, books must only be decrypted in a closed environment and a unique encryption key must be used for each user.
Notes
1. For example, on February 3, 2000, Wired News reported that "BMG Germany says it has a major piracy problem on its hands, blaming rampant copying of audio CDs for a drop in music sales."
2. On August 19, 1999, CNet News reported "A day after Microsoft released its new web music technology, the company confirmed that crackers have already developed a program to skirt the security behind it."
3. As reported in CNN.com on November 5, 1999.
Martin F. Eberhard is cofounder and chief executive officer of NuvoMedia, Inc.
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