Re: Help with DH key exchange on SSHv2.0

[Manik Surtani <manik.surtani%conchango.com@localhost>]

Hi, Marcus.



Markus Friedl wrote:
> On Tue, Jul 02, 2002 at 10:36:15AM +0100, Manik Surtani wrote:
>
> > Hey all.
> >
> > Apologies if this is the wrong place to post this question.
> >
> > I'm developing an open source Java SSH (v2) client API, and need a bit 
> > of help.
> >
> > 1) After receiving the KEXDH_RESPONSE packet, reading SSH Transport 
> > Layer Protocol (March 2002), Section 5.2, Output from Key Exchange:  do 
> > I assume that, in HASH (K || H || "A" || session_id), H is a mpint?  The 
> > spec states that K is a mpint but doesnt specify for H.
>
>
> check draft-ietf-secsh-transport-XX, and search for
>    The hash H is computed as the HASH hash of the concatenation of the
>    following: ...
>
> H is a hash, it's the raw output of sha1, in the 
> "diffie-hellman-group1-sha1" key exchange.


Yes, I have already computed H - and have it as a byte[].  But does it 
need to be encoded as a mpint, or a string, or just raw bytes for the 
HASH (K || H || "A" || session_id) operation?


> > 2) Also, how do I communicate my public key to the server?  From the 
> > spec, I gather that the next packet to send is a SSH_MSG_NEWKEYS with no 
> > data following ... am I wrong?
>
>
> check draft-ietf-secsh-transport-XX, and search for
>
>    First, the client sends the following:
>
>      byte      SSH_MSG_KEXDH_INIT
>      mpint     e

I have already done SSH_MSG_KEXDH_INIT and have received 
SSH_MSG_KEXDH_REPLY.  Is the next step just SSH_MSG_NEWKEYS, then?


Also,

3)  The keys generated using HASH(K || H || "A" || session_id) - which 
key do I use for the SSH-AUTH procedures?  Is it Initial IV client to 
server?

Thanks ...

Manik

> -m
>
> _____________________________________________________________________
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