Martin Deubler Johannes Grünbauer Gerhard Popp Guido Wimmel Chris Salzmann 99-108 2004 conf/apsec/2004 APSEC http://doi.ieeecomputersociety.org/10.1109/APSEC.2004.101 db/conf/apsec/apsec2004.html#DeublerGPWS04