1. Evaluating New Copy-Prevention Techniques for Audio CDs
John Alexander Halderman
Princeton University
Department of Computer Science
Presentation by: Sau Fan Lee

2. What this Paper is About
A detailed report on an experiment carried out to analyze the effectiveness of some recent new copy-prevention techniques for Audio CDs.
An analysis of the inner workings of these new techniques in order to find out how they work.

3. History
Recently, a new family of copy-protection methods have been invented to allow Audio CDs to be played only on normal CD players.
Computer CD-Rom drives won’t be able to read or play them (generally).
Details on how these techniques work are undisclosed so as to provide “security through obscurity”.

4. Criticisms
The experiments only use a very small number of samples for testing (CD-Rom drives, CD software, types of copy-protected Audio CDs), and not all combinations of the samples are used. Thus, they are unlikely to portray the effectiveness of the copy-prevention techniques for Audio CDs as a whole.
The report failed to consider the fact that selective track-ripping can still be done (eg. through Nero Burning Rom), and re-encoding of the track songs is also possible for CDs that provide encrypted versions of the tracks for playing on Windows.

5. Appreciations
The paper is very easy to read and follow. Simple English is used throughout the article.
Given the limited resources and samples available for testing, the authors did a very good job in analyzing what techniques are used on each copy-protected Audio CD.
The author also compared his results and analysis with other articles on the same topic to produce reliable conclusions on how the techniques work and what ways can be used to override them.

6. How do these Techniques Work?
Unlike computer CD-Rom drives, most normal CD players tend to ignore parts of the CD-Rom standards that are not relevant to audio.
Most computer CD-Rom drives (and CD software) are not well-designed to handle or correct errors on CD-Roms.
Most normal CD players are not multi-session aware, so they are only able to read the first session of a multi-session CD.
Thus, audio CD copy-prevention techniques deliberately inject errors onto parts of the CDs that are ignored by most normal CD players.

7. Types of Techniques Invalid track type (Data instead of Audio).
Invalid starting time for first track (less than 2 seconds).
Invalid sessions or session information beyond the first session of a multi-session CD.
Non-existing tracks.
Non-existing sessions.
Invalid start times for all the tracks on first session.

8. Effectiveness of the Techniques
The copy-prevention techniques only work on some current computer systems.
They caused problems on many newer portable and car CD players that are multi-session aware.
They can be bypassed easily using the right computer software and hardware, or by drawing around the outer rim of the copy-protected Audio CDs with a black felt-tip pen.
Most CD software have already been modified to cope with these copy-prevention techniques only a few months after the techniques are used on Audio CDs.
All in all, these copy-prevention techniques are very ineffective and usable in only a short period of time before becoming completely worthless.

9. Question
Even if these techniques do work effectively, why would consumers want to buy these copy-protected Audio CDs knowing that they can’t play them on computers, copy them to MP3 players, or make backup copies of them?