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  • From: "Sergey A. Lipnevich" <sergey AT optimaltec.com>
  • To: sm-discuss AT lists.ibiblio.org
  • Subject: Re: [SM-Discuss] Compromise on signatures
  • Date: Tue, 30 Aug 2005 23:53:48 -0400

Quoting Seth Alan Woolley <seth AT positivism.org>:

Adding a length to a hash outside the hash is one more level of
difficult for an attacker attempting to use massive appends to gain a
collision (which is a totally different way than the technique above).
Sergey is trying to prevent:

sfsfasdfs = 46643
sfsfasdfsfsdfasdfamaliciouscodefsdfsdfadfd = 46643

Completely different problem.

Yes, that's what I meant. Using "massive append" would be impossible if we
include the length. However, what I don't know is what's the easier way to find
a collision: looking for different data of the same length, or
appending/removing data. If the latter is a trivial task, we will improve the
chances against hash collision significantly. But if collision by
appending/removing bytes is difficult, we're not going to gain much protection.

See extract from the article you already linked to :):

I should read this article...

Thanks,
Sergey.





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