Protect ADB access via network? I have several Android devices in a local network. (Android Set Top Boxes from Geniatech, running 4.2 Jelly-Bean)
If these boxes have problems or need debugging, I simply connect to them via 

adb connect ip-address


there I have full access to the (rooted) devices.

Unfortunately everybody in the network has this possibility. I understand that it is the responsibility of the network admin, to protect it against hackers and stuff, but I would like to add additional security. So my question is:

Can I somehow protect the adb-connection to the Android with a password?  (or a Certificate or something) Or does anybody of you know alternatives? 

ADB must remain open, so I can access the devices from the network, e.g. to directly make apk-updates, or read the logfiles.

Best regards
As suggested by @Izzy I am going for the "firewall-solution":

Block all connections for the adb-port (5555), except from my trusted devices.

Thanks again!