This is copied from the airberlin website.
And 1h20m is more than enough, assuming no flight delays.

Transferring from a long-haul to a short-haul flight:
When you have gone through passport control, just follow the signs for "Departures B". You will not be leaving the customs area. Nevertheless, you will need to observe the regulations for carrying liquids in your cabin baggage, as another security check will be required on entry into an EU country. Passengers already in possession of their boarding pass for the connecting flight can go straight to their departure gate. Passengers without a boarding pass for their connecting flight should contact the airberlin transfer counter in Arrivals C, after passport control, or in Departures B, after the security check E1.

http://www.airberlin.com/site/airpor...ng&checkNavi=1