Transcript Evaluating New Copy-Prevention Techniques for Audio CDs

Evaluating New Copy-Prevention
Techniques for Audio CDs
J. Alex Halderman
Princeton University
Department of Computer Science
Copy-Resistant CDs - Overview
• Modified discs
– Play on CD players, hard to read on PCs
• Response to “consumer piracy”
• Deliberate errors
– Audio data / metadata
• Variations from several vendors
• Few discs today; many coming soon
– BMG, EMI, etc.
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Notable Drawbacks
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•
•
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Primarily affects legitimate CD owners
Confusing hardware/software errors
Violates standards, bad engineering practice
Effectiveness for reducing unlawful copying
hasn’t been demonstrated
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Interesting Questions for C.S.
1. Are they effective?
2. How do they work?
3. Can they be defeated?
Who wants to know?
Record companies, musicians,
policy makers, software authors,
music buyers, researchers
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Tested Three Discs
Music City, 2001
Universal, 2001
Columbia/Sony, 2002
MediaCloQ
(SunnComm)
Cactus Data Shield
(Midbar)
key2audio
(Sony)
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Not Addressed
Why would anyone want to copy these discs?
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Question 1
Are these techniques effective?
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Test Configurations
Covered range of deployed systems
• Operating System
– Windows, Linux
• Hardware
– Toshiba, Hitachi, IBM, Plextor drives
• Software
– CD Player, MusicMatch, Nero, CloneCD (Windows)
– CDP, CD Paranoia, CDR-DAO (Linux)
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Test Results
OS
Drive
Software
Result
Win 98
Toshiba
*
0/9
Win
2000
Hitachi
IBM
Sony
CD Player
MusicMatch
Nero
0/9
0/9
0/9
CloneCD
6/9
CD Player
MusicMatch
Nero
0/3
0/3
0/3
CloneCD
3/3
CDP
CDR-DAO
0/3
0/3
CD Paranoia
1/3
CDP
CDR-DAO
0/3
0/3
CD Paranoia
3/3
Plextor
Linux
Hitachi
Plextor
• Variety of errors
– disc not detected
invalid data
crashes
– Toshiba drive broken
until reboot
• Most tests failed (62/75)
• Some successful
– CD Paranoia, CloneCD
(Plextor hardware)
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Implications
• Seemingly effective today against
deployed hardware, typical applications
• Some configurations already can play
– Greater compatibility is possible
• Different modes of failure
– Schemes use slightly different measures
(more detail later)
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Question 2
How do these techniques work?
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How Do These Schemes Work?
• Exploit bugs, lack of robustness
in hardware and software
– Unexpected deviations from standards
• Two levels of failure
– Hardware: Drives reject the discs (firmware)
– Software: Apps fail even on “working” drives
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•
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Session 1
TOC
Track 1
Track 2
…
Session 2
TOC
Track
Track
…
…
CD drives
CD players
Normal CD Structure
Discs divided into tracks
Tracks listed in table of contents (TOC)
May be grouped into sessions
Drives read TOC from each session,
return list of tracks
• CD players only see session 1
• Observed two main categories of
deviations
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• Invalid TOC entries in
session 2
– Bad track locations
– Audio marked as data
Session 1
Real TOC
Track 1
Track 2
…
Session 2
Fake TOC
Data Track
CD drives
CD players
Fake TOC Entries - Software
• Drive returns invalid listing,
fools software
• CD players only read first
session, unaffected
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• Session 2 contains pointer to fake
session near outer edge of disk
Session 1
– Incomplete TOC, no lead out
– Fatal errors in some hardware
(e.g. Toshiba)
Real TOC
Track 1
Track 2
…
• Possible variations
Session 2
Fake TOC
Fake Session
CD drives
CD players
Fake Session Pointers - Hardware
– No pointers to earlier sessions
– Physical incompatibilities making
earlier session hard to reach
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Question 3
Can these techniques be defeated?
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Felt-Tipped Pen Hack
(Appeared on Chip.de early May 2002)
• Hides last TOC
containing invalid track/
session entries
• Drives see only first
TOC, so disc can be
read normally
Last TOC area
obscured by marker
Outlaw felt-tipped pens!
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How to Adapt Hardware
• Direct fix — “compatibility mode”
– Emulates CD player
– Not even necessary
• Indirect fix — greater robustness
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–
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Fix bugs (firmware)
Better error reporting
More robust failure modes
Error interpolation
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How to Adapt Software
• Bug fixes, greater robustness
– Ignore obvious errors (warnings, not failure)
– Scan for track starts by binary search
– Interpolate over missing samples
• Changes ensure maximum compatibility
with all faulty discs, not just copy-protected
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Change is Underway
• Software
– Audiograbber, CloneCD, and EAC have modes
for handling protected discs
• Hardware
– Plextor, others work today
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Can They Be Defeated?
• Yes!
– Offer minimal protection today, but will be
easily adapted to (already happening)
– Rate of adaptation proportional to rate of
deployment
– Schemes ineffective against copying in the near
future (by the time they are widespread)
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Conclusions
• Partial incompatibility with spec. won’t work
– Software too easy to adapt and distribute
• Takes advantage of HW/SW flaws
– Prohibiting circumvention would be to mandate bugs!
• Relies on stopping reading in most cases –
but can be copied online if just some can read
– True for tested discs
– Circumvention easy, can’t be stopped everywhere
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Conclusions
• In present form, these schemes are
worse than useless
–
–
–
–
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“Bad hacks”
Won’t prevent illegal copying
Inconveniences legitimate music owners
May make people less willing to buy CDs
Further alienates public from music industry
• Industry must find an alternative
– DRM? New business model?
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