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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 23:40:27 -0400

Quoting Mads Laursen <smgl AT dossen.dk>:

On 30/08/05 15.05, Sergey A. Lipnevich wrote:
Quoting Seth Alan Woolley <seth AT positivism.org>:

>
> size of tarball doing what exactly?

The first way that comes to mind to generate a hash collision is to add
bytes to
the file until the collision is achieved. If we include both the hash
value and
the tarball size in the DETAILS, we're drastically reducing chances of hash
collision going unnoticed.

That is actually wrong. Most hash functions use the Merkle-Damgaard
structure[1], which explicitly include the length in the hashed data,
in the final block. So actually finding a collision of a different
length would be (at least) as difficult as finding one of the same
length. At least, that is how I understand it.

OK, I'm sorry I said that. I knew the fact that the length is included in the
hash calculation, but I had (still have I guess) a very primitive understanding
of collision-generation techniques. Apparently there's much more to it. Thanks!
I actually learned something in this discussion :-O...

Sergey.





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