source : https://blog.aaronlenoir.com/2018/05/06/ssh-into-synology-nas-with-ssh-key/
ssh-keygen -t rsa -b 4096 -C "user@machine"
in /etc/ssh/sshd_conf
PubkeyAuthentication yes
sudo -i chmod 755 /myvolume1/homes/myuser synosystemctl restart sshd.serviceto debug :
/bin/sshd -d -p 1234