Re: constructing a specified hash function
 From: "bobic" <fbloveu@xxxxxxxxxxx>
 Date: 31 Oct 2006 23:58:19 0800
David Wagner wrote:
bobic wrote:
Hi, all. Recently, I want to construct a specified hash function, which
satisfies
y=h(x), x can be any string, and y must belong to [g^a mod p,g^{a+1}
mod p,...,g^b mod p], and no body knows the discrete logrithm of y
based on g. a,b are known.
How about h(x) = G * g^H(x), where G = g^a mod p and
H(x) = SHA256(x) mod (ba)/ Does that do it? Note that you will
have to publish the values G and ba, but you nobody needs to know
the discrete log of G to the base g, nor the discrete log of y to
the base x.
Out of curiousity, why do you want this hash function? Do you
have any particular security goals for it?
No! :( It cannot catch the goal.
In your way, though nobody knows the discrete logrithm, everybody knows
that h(x) is the product of a constant and a number with a known
discrete logrithm.
If the constant changes to a variant, it is ok!
Or if the number changes to be with a unknown discrete logirhtm, it is
also ok!
Thanks for your reply!
.
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