Gen Kitagata Debasish Chakraborty Satoshi Ogawa Atsushi Takeda Kazuo Hashimoto Norio Shiratori Visitor Access Control Scheme Utilizing Social Relationship in the Real World. 95-107 2010 IFIPTM http://dx.doi.org/10.1007/978-3-642-13446-3_7 conf/ifiptm/2010 db/conf/ifiptm/ifiptm2010.html#KitagataCOTHS10