# Re: EC Key Derivation Problem

*From*: Fabrice <fabrice.gautier@xxxxxxxxx>*Date*: Thu, 13 Mar 2008 16:51:28 -0700 (PDT)

On Mar 13, 4:39 pm, Fabrice <fabrice.gaut...@xxxxxxxxx> wrote:

Hi,

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 ?

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...

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

without knowing the private root key.

Thanks

What about: f(a,k)=a*k and F(A,k)=k.A

Then:

b=f(a,k)=a*k (in Fp)

so:

F=(A,k)=k.A=k.(a.P)=(k*a).P=b.P=B ?

Does this works?

.

**References**:**EC Key Derivation Problem***From:*Fabrice

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