Can we disable diffie-hellman-group-exchange-sha1 by default?

Yegor Ievlev koops1997 at
Fri Feb 15 10:56:56 AEDT 2019

Can we disable diffie-hellman-group14-sha1 too?

On Thu, Feb 14, 2019 at 10:23 PM Mark D. Baushke <mdb at> wrote:
> Hi John,
> The short answer is YES.
> Jon DeVree <nuxi at> writes:
> > I ask because the removal of diffie-hellman-group-exchange-sha1 happened
> > accidently in 7.8 due to a mistake in a change to readconf.c. I noticed
> > this and filed a bug about it along with a patch to fix readconf.c to use
> > KEX_CLIENT_* like it used to:
> The diffie-hellman-group-exchange-sha1 is an optional key exchange
> method provided by RFC4419 and updated by RFC8270.
> Support for it is not required and may (and in my opinion should) be
> disabled by default without any impact to the SSHv2 protocol.
> The only two Mandatory To Implement (MTI) key exchange methods are those
> in RFC3253 (diffie-hellman-group1-sha1 and diffie-hellman-group14-sha1).
> Even though they are MTIs, that just means you need to be able configure
> them, there is no mandatory requirement that a given installation enable
> them by default.
>         Enjoy!
>         -- Mark
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