MD5 Collisions...

[Josh Paetzel]

On Tuesday 04 December 2007 09:40:58 am Eygene Ryabinkin wrote:
> Matt, good day.
>
> Tue, Dec 04, 2007 at 09:19:58AM -0500, Matt Piechota wrote:
> > Norberto Meijome wrote:
> >>  I understand that the final nail in MD5's coffin hasn't been found
> >>
> > > yet ( ie, we cannot "determine the exact original input given a
> > > hash value") , but the fact that certain magic bytes can be found
> > > (rather quickly) so that any 2 given binaries end up as collisions
> > > seems , from my unlearned POV, more serious or sinister than what
> > > the text above implies.
> >
> > I think the big mitigating factor is that you can't easily generate a
> > message that has the same length as the original as well as the same
> > hash.
>
> No, read Kaminski's paper (http://www.doxpara.com/md5_someday.pdf):
> with Wong's and Joux's multicollision attack (or its extensions)
> one can generate files with the same sizes and MD5 hashes.
>
> The usefullness of this with application to the ports collection
> is questionable, since you should make two colliding archives and
> both of them should be unpackable and the second should do some
> evil things.  But strictly speaking, there are attacks producing
> files with the same size and MD5 hash.
>
> http://www.cits.rub.de/MD5Collisions/ is also a good reading.

It's not really questionable....for all practical purposes it's worthless.  In 
order to generate meaningful same-length collisions you need control of the 
original file.  (Your links go to lengths to explain this...) In the case of 
a ports distfile if you have control of the original file you really don't 
need to go to great lengths to generate collisions, you can simply toss your 
malicious content in there right from the get go.

-- 
Thanks,

Josh Paetzel

PGP: 8A48 EF36 5E9F 4EDA 5A8C 11B4 26F9 01F1 27AF AECB
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