phc-discussions - Re: [PHC] friendly warning about randomness tests

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Message-ID: <20140901215308.67212f2c@lambda>
Date: Mon, 1 Sep 2014 21:53:08 +0000
From: Brandon Enright <bmenrigh@...ndonenright.net>
To: Rich Felker <dalias@...c.org>
Cc: discussions@...sword-hashing.net, bmenrigh@...ndonenright.net
Subject: Re: [PHC] friendly warning about randomness tests

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On Mon, 1 Sep 2014 17:17:40 -0400
Rich Felker <dalias@...c.org> wrote:

> For reference with regard to how meaningless these tests are, a 32-bit
> LCG with a trivial tempering function taken from MT applied to the
> output can pass most if not all of dieharder. (I'd have to recheck to
> confirm that it's all, but I seem to remember it being all when I was
> developing that code.)
> 
> Rich

Yes.  Nmap (the port scanner) uses a LCG with some basic tweaks to it
for generating "random" IP addresses to be scanned without producing
any duplicates before cycling through all 2^32 IPs (Nmap's -iR feature).
This passes every Dieharder randomness test.  It's probably not
surprising but Dieharder doesn't have a check for treating the output
as 32 bit numbers and then looking for expected duplicates.  If it did
though Nmap's PRNG would obviously fail.

Randomness tests give me zero additional confidence in any candidate.

Brandon

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