Yuko Tamura Atsuko Miyaji Anonymity-Enhanced Pseudonym System. 33-47 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2846&spage=33 2003 conf/acns/2003 ACNS db/conf/acns/acns2003.html#TamuraM03