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bluesky - Re: User Anonymity

bluesky AT lists.ibiblio.org

Subject: Global-Scale Distributed Storage Systems

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  • From: hal AT finney.org
  • To: bluesky AT franklin.oit.unc.edu
  • Subject: Re: User Anonymity
  • Date: Sat, 17 Feb 2001 11:55:24 -0800


David Hopwood writes:
> If the blocks stored by servers encode information about more than one
> (unrelated) file, then it is more difficult for the enforcers to argue
> that any particular blocks should be banned. Marc Waldman and David
> Mazières have a paper on a design that does this (using a variant of
> Shamir secret sharing); they call it "entangling" files. It looked to
> me as though this idea could be added on to almost any system. I'll ask
> them whether the paper can be put on the web.

I heard the Freehaven developers were looking at this concept. A similar
idea was proposed by David Madore [1]:

: The principle is very simple. People distribute samples of random
: data. We call these samples pads. A pad is a file containing random bits,
: completely indistinguishable from white noise, and of a fixed length. I
: propose a standard length of 128kB (131072 bytes) for each pad.
: ...
: Each pad by itself is completely without value. It is a mere hunk of
: random data. However, if you combine several pads together by XORing them,
: you can recover some data that are hidden in the pads. The information is
: in no single pad, but it is somehow delocalized in all the pads together.
:
: The point is that if a suppressed piece of information can be recovered
: from combining n pads (and no less), no single person is distributing
: anything of value since all he is doing is givint out a sample of random
: data. Indeed, most of them might not even be aware that their pad can
: be used to produce the information in question.
:
: Again, each pad is truly mathematically indistinguishable from
: random noise, and it is completely impossible, in the absence of date
: information, to know who put the data in a set of pads.

In the context of U.S. law, the question is what your obligations are
under the DMCA with this system. If you publish a random pad, and you
are informed by a copyright owner that your pad, when xor'd with five
others, produces some infringing data, are you obligated to take it down?
The DMCA does not list "it would destroy other data" as a justification
for refusal.

One possible point of weakness with this method (and with the
hide-the-server approach) is that the censors can go after the name
lookup portion. For file entanglement to work there must be an index
somewhere that says, for file so-and-so, combine these 5 files from
the system. The DMCA lets owners take down links to infringing data,
so they could go after this part and then no one could find anything.

Hal

[1] http://www.eleves.ens.fr:8080/home/madore/misc/freespeech.html




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