were confusingly worded, were written in tiny print, and did not say explicitly that software would install or
run immediately upon insertion of the disc. Some in the record industry argue that the industry's desire to
block potential infringement justifies the short-term execution of the temporary protection software on every
user's computer. We think this issue deserves more ethical and legal debate.
4.3
Passive Protection
Another way to prevent copying before active protection software is installed is to use passive protection
measures. Passive protection exploits subtle differences between the way computers read CDs and the
way ordinary CD players do. By changing the layout of data on the CD, it is sometimes possible to confuse
computers without affecting ordinary players. In practice, the distinction between computers and CD players
is imprecise. Older generations of CD copy protection, which relied entirely on passive protection, proved
easy to copy in some computers and impossible to play on some CD players [12]. Furthermore, computer
hardware and software has tended to get better at reading the passive protected CDs over time as it became
more robust to all manner of damaged or poorly formatted discs. For these reasons, more recent CD DRM
schemes rely mainly on active protection.
XCP uses a mild variety of passive protection as an added layer of security against ripping and copying.
This form of passive protection exploits a quirk in the way Windows handles multisession CDs. When CD
burners came to market in the early 1990s, the multisession CD format was introduced to allow data to be
appended to partially recorded discs. (This was especially desirable at a time when recordable CD media
cost tens of dollars per disc.) Each time data is added to the disc, it is written as an independent series of
tracks called a session. Multi-session compatible CD drives see all the sessions, but ordinary CD players,
which generally do not support the multisession format, recognize only the first session.
Some commercial discs use a variant of the multisession format to combine CD audio and computer
accessible files on a single CD. These discs adhere to the Blue Book or "stamped multisession" format.
According to the Blue Book specification, stamped multisession discs must contain two sessions: a first
session with 199 CD audio tracks, and a second session with one data track. The Windows CD audio
driver contains special support for Blue Book discs. It presents the CD to playing and ripping applications
as if it was a normal audio CD. Windows treats other multisession discs as data-only CDs.
XCP discs deviate from the Blue Book format by adding a second data track in the second session. This
causes Windows to treat the disc as a regular multisession data CD, so the primary data track is mounted as
a file system, but the audio tracks are invisible to player and ripper applications that use the Windows audio
CD driver. This includes Windows Media Player, iTunes, and most other widely used ripper applications.
We developed a procedure for creating discs with this flavor of passive protection using only standard CD
burning hardware and software.
This variety of passive protection provides only limited resistance to ripping and copying. There are a
number of well-known methods for defeating it:
· Advanced ripping and copying applications avoid the Windows CD audio driver altogether and issue
commands directly to the drive. This allows programs such as Nero [24] and Exact Audio Copy [33]
to recognize and read all the audio tracks.
· Non-Windows platforms, including MacOS and Linux, read multisession CDs more robustly and do
not suffer from the limitation that causes ripping problems on Windows.
· The felt-tip marker trick, described above, can also defeat this kind of passive protection. When the
second session is obscured by the marker, CD drives see only the first session and treat the disc as a
regular audio CD, which can be ripped or copied with ease.
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