You should know that Android 4.2.2 (or just before) introduced RSA key checking for adb access. – The device asks now if you want to allow access.
To avoid asking every time, the computer presents an RSA key, which can be permanently accepted.
The dialog on the phone shows the RSA key fingerprint. – On Linux, the public/secret key pair is here:
How can I show the fingerprint of that key file? (I’m looking for a command line to do that on the Linux system.)