Re: Making a weak Hash stronger until a fix comes along -- concatenation of hash functions... .2: Concatenation
From: David Wagner (daw_at_taverner.cs.berkeley.edu)
Date: 09/27/05
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Date: Mon, 26 Sep 2005 23:13:26 +0000 (UTC)
Max Power wrote:
>My use of concatenation was not totally clear.
>I would never consider adding the strings of the 2 hashes together.
We understood that. As I and another poster have both pointed out,
there are attacks on concatenation (see Joux's multi-collision work)
which show that concatenation adds a lot less security than you might
think.
Taking the hash and feeding it into another hash function doesn't
help. If you use g(f(x)) as your hash function, and if f(.) has
collisions, then so will g(f(.)). Think about it.
Salts don't help, either.
>True, it is not a perfect solution -- but merely an adequate one.
Unfortunately, the proposals you presented are neither adequate nor
a solution, I'm sorry to say.
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