to increase security on an sshd server, and assuming you have
registered your ssh keys ahead of time in authorized_keys, then
this bit goes in /etc/sshd_config (at the end works fine):

##############

# fred mods 2019-02-19:
# trying to keep intruders out...  this disables password logins.
# also of course disables root logins, which should already have been done.
PermitRootLogin no
ChallengeResponseAuthentication no
PasswordAuthentication no
UsePAM no

##############