In any sane world we would have retired SSHv1 by now. All the
operating systems we use have. Sadly, we have these 2511s that are
still wandering the night in ghostly torment.
So we need, not a backport, but a foreport of ancient code that's been
retired for good reason. Sigh.
Starting with the Debian source package for the last version that
supported SSHv1, then hacking as needed.