Matthias Kabatnik Alf Zugenmaier Location Stamps for Digital Signatures: A New Service for Mobile Telephone Networks. 20-30 2001 conf/icn/2001-2 ICN (2) http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2094&spage=0020 db/conf/icn/icn2001-2.html#KabatnikZ01