Source: http://wiki.qedinux.be/index.php?title=BackInTime_to_Synology_DSM_5 and: http://techanic.net/2014/04/12/configuring_ssh_and_scp_sftp_on_dsm_5.0_for_synology_diskstations.html
Not everything here is explained. You need to know what you do. Also: DSM Updates will change your settings!