MacOS X High Sierra and X11 Forwarding using SSH
After installation of High Sierra we recognized that a ssh connection to other systems show up a warning:
Warning: untrusted X11 forwarding setup failed: xauth key data not generated.
This happens when you installed the latest release from XQuartz 2.7.11 during the last year or so. It seems that the installation of High Sierra replace a couple of files even if they are related and needed by other applications - like XQuartz. To solve this issue just reinstall XQuartz 2.7.11.