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Subject: Global-Scale Distributed Storage Systems

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  • From: graydon AT venge.net
  • To: Global-Scale Distributed Storage Systems <bluesky AT franklin.oit.unc.edu>
  • Subject: Re: Think cash
  • Date: Fri, 9 Mar 2001 08:16:33 -0500


On Fri, Mar 09, 2001 at 02:17:47AM -0600, Tony Kimball wrote:

> It seems not so hard to me.

this is precisely the matter which is troubling about these comments.
caesar ciphers "seemed" pretty hard too. an awful lot of work has gone
into classifying exactly _how_ hard certain problems are, within a
framework of more clearly defined mathematics. while it may be true that
the human brain has a "leg up" on certain types of problems, we have
essentially no theoretical work to tell us _how much_ of a leg up it is,
what sort of computational problems the leg up depends on, and why we
should think that these computational problems are of the sort where the
person with a leg up can consistently "scale" the problem difficulty to
adapt to a persistent attacker.

moreover, the (brief) bit of cognitive science I got lead me to believe
that scaling the computational power of the human brain is not really
the sort of thing we know how to do anyways, so even if the leg up is
_theoretically_ scalable, I don't see why we should expect a human
interface to resist brute forcing, long term.

an example of a rediculously crude analysis: even assuming that there
is no such thing as pattern matching technology on computers, and they
are using memcmp to break your code, and humans have so much of a leg up
that they can pick out a _single_ salient bit of data in a full screen
truecolor image, the brute force solution is to take 1024 x 768 x (2^24)
images and write down what each of them is a picture of. do the math:

1024
768
2
24
^ 16777216
* 12884901888
* 13194139533312
1500000000
* 1440
* 2160000000000
/> 6.10839793208

so the people's republic of china, looking at 1 image a minute, could
completely defeat this system in 6 days. that is a quantitative
statement, admittadly bogus, but it illustrates the point: until
you ground your problem model in some math, you are _not_ making
quantitative statements but rather waving your hands, and the people in
the audience with enough experience watching people wave their hands (or
enough experience waving our own hands) will be justifiably skeptical.

-graydon




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