Firewall denies sshd-keygen-wrapper despite configuration
I was having the same problem and this is how I fixed it --


Delete sshd-keygen-wrapper from firewall list
Click + to add it back
In the Open dialog press Cmd-Shift-G and specify /usr/libexec
select sshd-keygen-wrapper 


Explicitly adding it in this way worked for me.  Good luck!

After step 4. you have to reboot. Or just restart the firewall by disabling and enabling the firewall in the system settings. Without the restart the new configuration will not be activated.