How do I setup sshd on Mac OS X to only allow key-based authentication?
After a little trial and error, I found the answer myself. These options need to be set in /etc/sshd_config:
PasswordAuthentication no
ChallengeResponseAuthentication no
Only changing one of them is not enough.
In /etc/ssh/sshd_config
# To disable tunneled clear text passwords, change to no here! Also,
# remember to set the UsePAM setting to 'no'.
#PasswordAuthentication yes
#PermitEmptyPasswords no
Set PasswordAuthentication to no and remove the # before it.