[linux-elitists] "DCMA"

Don Marti dmarti@zgp.org
Sat Apr 21 09:05:15 PDT 2001

begin  Karsten M. Self quotation of Sat, Apr 21, 2001 at 12:29:00AM -0700:

> Speaking o'wot, any idea what whatermarking Napster's going to be using?

Napster isn't planning to use watermarking. They're using "audio
fingerprinting" which is much different.

In watermarking, you try to label many tracks with a few inaudible marks
signifying something like "COPY PERMITTED" "NO HEADPHONE LISTENING
Devices or prorietary software are then expected to enforce these marks.
Watermarking is _very difficult_ because (1) anybody can look at many
files with the same mark to try to discern a pattern and (2) a good
lossy audio compression algorithm _discards_ inaudible information,
including watermarks.

(This raises the whole question of which prison you get thown into for
making a better codec that has the side effect of removing a watermark,
but I digress.)

> It's apparently vended by Relatable, and utilizes extant characteristics
> of sound recordings to identify them.  Appears to be a different beast.

Much different. "Audio fingerprinting" uses audible characteristics of
a track, not an inaudible mark. The reason that fingerprinting is
impractical for an SDMI-like system is that the database of fingerprints
is huge and won't fit in an inexpensive audio player. This restriction
doesn't apply to a system like Napster.

Of course, you have to tweak it. If you want to prevent people from
downloading "Louie Louie" and you happen to either (1) lock out one
rip of "Louie Louie" but not others or (2) lock out a bunch of other
songs with the same chord progression, no good. But fingerprinting
doesn't have the same tooth-fairy-powered-perpetual-motion-machine smell
to it that watermarking does.

I'm not saying that fingerprinting will work in Napster's case, since
unofficial clients will probably be able to fake their fingerprint
server right out of its socks.

Don Marti              "I've never sent or received a GIF in my life." 
dmarti@zgp.org            -- Bruce Schneier, Secrets and Lies, p. 246.
http://zgp.org/~dmarti/        (Free the Web: http://burnallgifs.org/)

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