Bug#1094246: openssh-server: postinst: please implement ssh-audit recommended keygen options

On Sun, Jan 26, 2025 at 06:09:25PM +0000, Colin Watson wrote:
> On Sun, Jan 26, 2025 at 07:53:26PM +0200, Martin-Éric Racine wrote:
> > I have noticed this as well e.g. whenever Debian ships a new
> > openssh-server package, I've had to manually run the command shown on
> > the hardening guide to remove modulus below 3272-bit all over again.
> 
> That's about DH moduli rather than host key sizes, right?  That feels
> somewhat different, because we just ship upstream's moduli file as a
> conffile, so providing any debconf-style control over that would be very
> difficult to do in a policy-compliant way.  (I'm also not sure what the
> compatibility implications are of dropping the smaller primes; I assume
> there must be some or upstream would probably have done it already ...)

Also, in https://bugzilla.mindrot.org/show_bug.cgi?id=2793#c1, Damien
Miller wrote:

  ... I don't think making people edit the moduli file is a great way to
  control which groups are negotiated. IMO a general MinimumDHSize
  option would probably be a better way to achieve this.

I tend to agree, so I think any effort in the direction of giving people
packaged ways to filter the moduli file (or whatever) would be better
directed towards adding something like MinimumDHSize upstream.  Then
that ssh-audit recommendation could just become adding a single line to
/etc/ssh/sshd_config.d/ssh-audit_hardening.conf.