Riccardo Focardi Flaminia L. Luccio Graham Steel Blunting Differential Attacks on PIN Processing APIs. 88-103 2009 NordSec http://dx.doi.org/10.1007/978-3-642-04766-4_7 conf/nordsec/2009 db/conf/nordsec/nordsec2009.html#FocardiLS09