SSH time increased significantly after upgrade to OpenSSH 9.6p1

[radiatejava]

Thanks Damien! Looks like quantum kex algo was the reason. After
changing to the traditional kex, ssh connections were fast enough.

On Mon, Jul 29, 2024 at 5:28 PM Damien Miller <djm at mindrot.org> wrote:
>
> On Sun, 28 Jul 2024, Darren Tucker wrote:
>
> > OpenSSH 9.0 introduced a quantum resistant hybrid kex method as the
> > highest priority method.  Quoting
> > https://www.openssh.com/releasenotes.html#9.0:
> >
> >  * ssh(1), sshd(8): use the hybrid Streamlined NTRU Prime + x25519 key
> >    exchange method by default ("sntrup761x25519-sha512 at openssh.com").
> >    The NTRU algorithm is believed to resist attacks enabled by future
> >    quantum computers and is paired with the X25519 ECDH key exchange
> >    (the previous default) as a backstop against any weaknesses in
> >    NTRU Prime that may be discovered in the future. The combination
> >    ensures that the hybrid exchange offers at least as good security
> >    as the status quo.
> >
> > This is more expensive than the previous defaults.  You can disable
> > this if necessary on either the server or client configs, see
> > KexAlgorithms in  ssh_config(5) and sshd_config(5).
>
> We should look at using an optimised version of NTRUPrime, at the moment
> we're just using a generic version that isn't very fast. There's probably
> a 3-5x saving to be made...
>
> -d