Re: Need Your Valuable Inputs for diffie-hellman-group14-sha256

[Jakub Jelen <jjelen@xxxxxxxxxx>]

On Thu, 2020-01-30 at 15:22 +0100, Andreas Schneider wrote:
> On Thursday, 30 January 2020 13:39:42 CET V Sidnal, Nagraju wrote:
> > Dear Team,
> 
> Hi Nagraju,
>  
> > We want to use libssh for our application to interact with SSH
> > Server.
> > We would like to know if libssh supports KEY_EXCHANGE =
> > diffie-hellman-group14-sha256.
> 
> we don't support it, as we have:
> 
> diffie-hellman-group18-sha512, diffie-hellman-group16-sha512
> 
> can't you use those? What is the reason for diffie-hellman-group14-
> sha256?

Hello,
The latest RFC mentioning this is RFC 8268 [1], which defines it as a
smooth transition (as the group14 is supported in all ssh
implementations and the change is only the the digest), but recommends
to avoid this group in other paragraphs. I found also some old drafts
suggesting that this should be mandatory, but neither of them got
published as a RFC in the end.

If it will turn out useful and needed for interoperability with
particular peer, implementing this should be very easy as we already
have all the primitives. But otherwise I would say that we will not
want another key exchange method with very similar security as we
already have.

[1] https://tools.ietf.org/html/rfc8268

-- 
Jakub Jelen
Senior Software Engineer
Security Technologies
Red Hat, Inc.