I read the paper, and the crux of the issue is not processing incoming data prior to passing it to a hashing function. I think its something ala
chomp($f = <>);
$input{$f}++;

[download]
Though it might be something closer to
chomp($f = <>);
if ( $input{$f} ) {
   blah;
}

[download]
The problem described is causing the hashing function to work harder to produce the hashed string... degrading performance to O(n * n) time frame. But it assumes the attacker has a quasi direct pipe to the hashing functions input.

There are situations where it makes sense to track data collected in a hash (letter/number counting comes to mind off the top of my head), but the type of pre constructed data that is required for this attack to be successful raises other questions in my mind.

If this is something other than trivial tracking of data, and is infact some larger piece of production code we are talking about then you don't trust anything coming in from outside, right??

I would be interested to hear what other monks think after reading the paper, personally it would be interesting to hear from individuals who actually work on the Perl codebase, and what they think of this situation. Also I didn't see any code to reproduce this, but I also didn't look too hard. I think I may revist this now though.

MMMMM... Chocolaty Perl Goodness.....

In reply to Re: Hash Clash on purpose by l2kashe
in thread Hash Clash on purpose by John M. Dlugosz

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