# Re: EC Key Derivation Problem

*From*: Kristian Gjøsteen <kristiag+news@xxxxxxxxxxxx>*Date*: Fri, 14 Mar 2008 07:22:35 +0000 (UTC)

Fabrice <fabrice.gautier@xxxxxxxxx> wrote:

Assuming a EC Private Key "a", and the public key "A=a.P"

I'm looking for a Private Key Derivation Function "f" and a Public Key

Derivation function "F" such that if "b=f(a,k)", then "B=b.P=F(A,k)"

Does such functions exist ?

I'm not really sure about what the point is, but the obvious answer is

that f is multiplication and F is point multiplication...

Actually I am sure they do (by definition) but do they have the

following properties:

- Is the knowledge of F gives any information about a, b, k or f ?

- Is the knowledge of f, k and b gives any information about a ?

- Is the knowledge of F, A and k gives any information about a or b ?

- Is the knowledge of F, B and A gives any information about k, a, or

b ?

- etc...

No, yes, yes, no, etc.

The main purpose is to be able to compute the derived Public Key

without knowing the private root key.

??

--

Kristian Gjøsteen

.

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