Angelos Stavrou John Ioannidis Angelos D. Keromytis Vishal Misra Dan Rubenstein A Pay-per-Use DoS Protection Mechanism for the Web. 120-134 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3089&spage=120 2004 conf/acns/2004 ACNS db/conf/acns/acns2004.html#StavrouIKMR04