Airplane boarding passes can be easily forged. But DHS is hoping your telephone can stop it. The idea is this. Sending boarding passes to mobile phones could prevent terrorists from getting on airplanes with forged documents. The system uses bar-codes that are displayed on the phone screen after the passenger has checked in using their phone. These are scanned at the boarding gate and are unique to each passenger and digitally signed, so pretty-much impossible to forge ahead of time. The trip is making sure every passenger has a compatible mobile phone.