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Subject: Re: 64-Bit random numbers (getting rather off topic)

Author: Dieter Buerssner

Date: 13:48:58 10/28/03

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On October 28, 2003 at 16:31:45, Dan Andersson wrote:

> Finding any periodicity with any reasonable amount of computation if those
>criterion are fulfilled should only be possible iff Integer Factorization is
>computationally easy. And the current bet is that it is hard as heck. The random
>properties of the algorithm are bound to that single assumption.

Hmmm, I see it a bit different from a general point of view (without looking
into the details of the algorithm). Your formula can never have a period longer
M, so it is trivial to find a periodicity in principle. Whether you can predict
the output of the next bit after you have known a (possibly large) number of
previous outputs, is another question (that seems very important for
cryptography). Some random source that produces a bitstream might produce 0 and
1 with different probabilities in a manner that is practically unpredictable.
Still, such a source would not be wanted normally (at least not with doing some
transformations) for statistical simulations. In most situations, it would give
wrong results. I don't say, that the Blum Blum Shub does have this properity -
just the "hard as heck" does not mean to me whether it has "good" statistical
properities. For example: How long must M be, that it will give me at least once
n ones in a row?

Regards,
Dieter



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