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Re: Jetty Session ID Prediction
From: Chris Anley <chris () ngssoftware com>
Date: Wed, 07 Feb 2007 12:29:21 +0000

Amit Klein wrote:
Chris Anley wrote:
Hi folks,
I've posted a paper that explains a little more here:
http://www.ngssoftware.com/research/papers/Randomness.pdf


Nice paper. I do notice an enumeration loop over 2^16 possible 16-bit
values. This can be improved as following (note: this is probably
already discussed in mathematic literature - i.e. I probably did not
invent it...):

<lots of cool stuff cut>

This should be much faster than looping over 2^16 values.

Cheers Amit, that's cool and I'm sure it's faster. There are quite a few
neat tricks in the literature - Knuth's paper on predicting lcg's where
you're missing the low bits is good (I was trying to work out whether
his technique and yours are equivalent; I'm still not sure...), and the
paper Michal Zalewski recommended:
http://dsns.csie.nctu.edu.tw/research/crypto/HTML/PDF/C89/138.PDF
is also neat. One interesting (?) question is whether that technique
applies to the mysql rand, which is wierd and custom, and used in the
auth protocol prior to version 4.1.

I don't think anyone's published the code for a totally generic
predictor before, but I might be mistaken. If anyone knows, could they
shout...?

Anyhow, ultimately, it's a POC for a specific bug.
I loop over 2^16 values because it's instant, and easy. :o)

Cheers,

     -chris.

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