On Fri, Aug 28, 2009 at 09:39:18AM -0400, Ram G wrote:
> Hello Users,
>
> I would like to run a design by you. The requirement (and the constraint) is
> that I have to design a secure communication channel without using
> certificates. I'm trying out DH key exchange.
>
> My proposed design is a two step process for communication:
>
> 1) Use Anonymous DH and estiablish the "shared secret". This is done at some
> predefined interval - may be once everyday or once every week.
>
> 2) In the second step of the communication, we will use the "shared secret"
> from step 1 for authentication. This will be done using Diffie-Hellman key
> exchange with pre-shared keys (DHE-PSK, support for which is added in
> version 1.0.0 )
>
> 3) Once the client is authenticated, all communication is encrypyted using
> the master secret derived from DHE-PSK.
>
> This removes the need for me to establish passwords before two parties can
> communicate and generates passwords on the fly.
>
> Will this secure me against man-in-the-middle attacks which is possible with
> anonymous DH and without authentication ?
No. Without a previously arranged shared secret and no trusted introducer,
authentication is *impossible*. Authentication is an act of recognizing
a party that posesses something you can verify. You CAN NOT generate
authentication secrets on the fly.
--
Viktor.
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