handling weak keys using random selection and CSPRNGs

Marcos el Ruptor Ruptor at cryptolib.com
Mon Oct 16 11:22:24 EDT 2006


> Now, you said "compressed files" and you might not have meant
> pictures, but note that L-Z style compressed files don't really have
> much in the way of headers. If the headers were a problem, you'd
> expect longer files to bury any deviation in the noise, but it
> doesn't. The longer the files I test the more certainly non-random
> they are.
>
> I stand by my statements.
>
> Greg.

Hello, Greg!

I did not say anything about pictures. I only said that it's not that hard 
to find a compression algorithm or a source of randomness or a simple PRNG 
that will pass all kinds of randomness tests. You said it's hard, I said it 
wasn't. Maybe you want to try testing something packed with WinRK or Durilca 
for example. You could probably even test the whole files packed with 
them...

Although I totally agree with you that JPEG or ZIP (Deflate) or LZ 
compressed data could only pass randomness tests if the data was random to 
begin with. But come on, such weak ancient algorithms hardly qualify as 
randomness benchmarks. Modern decent compression algorithms like those used 
in Stuffit or Allume reduce JPEGs by about 25% or so (losslessly). No wonder 
your tests show a bias!

On the other hand, maybe you have an amazing brilliant randomness test there 
that fails all the compressed files and makes diehard look like a baby's 
rattle... If that is the case, do share! ;-)

Ruptor 


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