Why copyright?
- Incentive to create stuff (US) and to promote cultural progress
- Authors can sell their copyrights
- Benefit to author weighed against other public goods.
Law grants exclusive rights to the author
- Copy and distribute
- Publicly perform
- Make a derivative work (translation, film based on novel)
- Covers expression, but no ideas
- Subject to �fair use� exceptions�parody, brief quotations. Factors: purpose and character of the use, nature of work, amount of material used relative to the whole, effect on market for original work.
First sale doctrine: allows resale, lending, etc.
These rules are for physical copies: Digital copies introduce new problems.
Transition to digital technology threatens balance.
- From buyer: ease of copying/redistribution
- From copyright owner: technologies of control, licensing
�Copy protection/prevention�/DRM.
Some general correspondence between legal rights and what technology enforces.
Common factors
- threat model assumes that file sharing is widely used.
- �Break once, infringe anywhere��once you can crack something, it can be copied or distributed everywhere. If someone can break your copy protection technology, anybody anywhere can infringe on copyright.
I.e. copy-protected CD�s. Lame approach, because player manufacturers will try to fix their players so that consumers who buy the drives can actually play their CD�s on the drives.
Distribute data in encrypted form.
Allow only authorized devices to learn the key.
- Pro: even if people get data, they can�t decrypt them.
- Device decrypts before playing content.
- Typical: each player device has own private key.
- Work is encrypted for a single player OR encrypted under session key, which is encrypted for a single player.
- Problem: no end-to-end protection. Content is vulnerable after decryption.
- Analog hole
- Problem: if someone can get the key, someone can build their own device to decrypt the data. Need tamper-resistant technology.
- Problem: installed base. People don�t buy new audio/video equipment very often.
Every time you sell, you put a serial number that uniquely identifies the copy.
Track who bought each copy so you know who to blame.
- Problem: Mark must be indelible (see later in lecture)
- Problem: practical details aren�t plausible.
- Hard to identify people
- Rely on store record clerks to record consumer names and ID�s accurately.
- What do you do when there are a million copies?
- Can�t be sure that if a person is accused, they are really guilty�what if stuff is stolen?
Mark attached to work, carries instructions about what to allow
- Player devices must protect the mark and obey it.
- Variants: Simple mark (bits in header) �broadcast flag�
- No attempt to prevent the removal of this flag.
- Watermark
- Subtle mark that�s in the content.
- Requirements: imperceptible, indelible (can�t remove w/out trashing the content), detectable by its plague
- Perceptual issues force per-medium solution
- Watermarking�end to end solution, i.e. if camcorder says �nope, I�m not recording THAT� to movie in the theater
- Theoretically dubious
- Bad track record
