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microsoft research drm talK
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Now, let’s apply this to DRM.
In DRM, the attacker is
also the recipient.
It’s not Alice and Bob
and Carol, it’s just Alice and Bob. Alice sells Bob a DVD. She sells
Bob a DVD player. The DVD has a movie on it — say,
Pirates of
the Caribbean
— and it’s enciphered with an algorithm called CSS
— Content Scrambling System. The DVD player has a CSS un-
scrambler.
Now, let’s take stock of what’s a secret here: the cipher is well
known. The ciphertext is most assuredly in enemy hands, arrr.
So what? As long as the key is secret from the attacker, we’re
golden.
But there’s the rub. Alice wants Bob to buy
Pirates of the Ca-
ribbean
from her. Bob will only buy
Pirates of the Caribbean
if he
can descramble the CSS-encrypted VOB — video object — on his
DVD player. Otherwise, the disc is only useful to Bob as a drinks-
coaster. So Alice has to provide Bob — the attacker — with the key,
the cipher, and the ciphertext.
Hilarity ensues.
DRM systems are usually broken in minutes, sometimes days.
Rarely, months. It’s not because the people who think them up
are stupid. It’s not because the people who break them are smart.
It’s not because there’s a flaw in the algorithms. At the end of the
day, all DRM systems share a common vulnerability: they provide
their attackers with ciphertext, the cipher, and the key. At this
point, the secret isn’t a secret anymore.
2. DRM systems are bad for society
Raise your hand if you’re thinking something like, “But DRM
doesn’t have to be proof against smart attackers, only average
individuals! It’s like a speedbump!”
Put your hand down.
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