Re: entropy

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Tim wrote:
> Using psuedo code, what it did was:
> 
>   x = random number between 1 and 200
>   y = random number between 1 and 200
>   draw dot at x,y
>   repeat
> 
> Now, considering that the random number is generated from white noise,
> there is no way for me to affect *how* the number is generated, all I
> can do is specify a range (there is no reseeding control for something
> that's generated from an uncontrolled white noise source), nor should
> any of my program code really be able to affect the random number, I
> expected that I'd get a random snow pattern drawn up over time.

The noise was probably not white.
If you have got diagonal parallel lines, the correlation between
two successive samples is almost for sure not 0. And white noise
implies zero autocorrelation at any non-zero distance.

Maybe the noise was somewhat white, but only upto a certain
frequency of the spectrum (no signal has infinite bandwidth) and
your fast sampling speed was beyond the limit.

Your "plot some graph" trick is actually a powerful way to detect
stupid random number generation, which can possibly lead to
significant security issues in some contexts.
See for example:

  http://lcamtuf.coredump.cx/oldtcp/tcpseq.html

(and so I push the thread to be more in-topic for this list) :-)

-- 
   Roberto Ragusa    mail at robertoragusa.it
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