Adam Muhlbauer Reihaneh Safavi-Naini Farzad Salim Nicholas Paul Sheppard Jan Martin Surminen Location constraints in digital rights management. 1173-1180 2008 31 Computer Communications 6 http://dx.doi.org/10.1016/j.comcom.2008.01.008 db/journals/comcom/comcom31.html#MuhlbauerSSSS08