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Subject: Re: randomness of random number generators? somewhat OT

Author: Dan Andersson

Date: 16:54:30 10/01/05

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On October 01, 2005 at 17:13:30, David Dahlem wrote:

>Is there any way to test the true randomness of various random number
>generators?
>
>Thanks
>Dave

1. True randomness is a property that only exists in generators with a physical
entropy source.
2. All Pseudorandom Number Generators have either a period or an increasing
storage space requirement.
3, Most PRNG's can be analyzed and shown not to be random without knowing the
period.
4. Some PRNG's are good enough that no predictiton better than P=0.5 can be made
about the value of the next bit given the preceding output.
5. A few PRNG's are irreversible even if you get access to its internal state.

 'True randomness' is only to be had by the first kind. PRNG's fulfilling case
four and five are as close as is possible. The Mersenne twister is good for most
any use but it is a class three PRNG.

MvH Dan Andersson



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