Remmina - The GTK+ Remote Desktop Client  v1.3.1
Remmina is a remote desktop client written in GTK+, aiming to be useful for system administrators and travellers, who need to work with lots of remote computers in front of either large monitors or tiny netbooks. Remmina supports multiple network protocols in an integrated and consistent user interface. Currently RDP, VNC, NX, XDMCP and SSH are supported.
Remmina-VNC-to-Raspbian-Stretch

The RaspberryPi Raspbian 9 default VNC server is RealVNC. RealVNC only supports 5 propertary security types: 5, 6, 13, 130 and 192. According to the official RealVNC documentation for the "Authentication" parameter, Authentication=VncAuth is the only scheme that allows direct connections from VNC-compatible Viewer projects from third parties.

In order to change to VncAuth scheme in your Raspbian and set a password to accept connections from Remmina VNC plugin, you have to:

  1. Open a SSH session or a terminal window to the raspberry
  2. As root, edit the file /root/.vnc/config.d/vncserver-x11
    3. Add the following lines at the end of the file
    Authentication=VncAuth Password=aa8ba782c23aff7e
    4. Save the file.
    5. Restart the VNC server service with
    ```sudo systemctl restart vncserver-x11-service

The above encrypted password is remmina, if you want to change it, type sudo vncpasswd -service and restart the VNC server service with sudo systemctl restart vncserver-x11-serviced

References:

[1] IANA: Remote Framebuffer Security Types [2] RealVNC: VNC Server parameter reference