[Unit]
Description=Dropbear RSA Keygeneration.
After=syslog.target
Before=dropbear.service
ConditionPathExists=!/etc/dropbear/dropbear_host_rsa_key

[Service]
Type=oneshot
ExecStart=/usr/bin/dropbearkey -t rsa -f /etc/dropbear/dropbear_host_rsa_key
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target