Hisayoshi Sato Tsuyoshi Takagi Satoru Tezuka Kazuo Takaragi Generalized Powering Functions and Their Application to Digital Signatures. 434-451 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2894&spage=434 2003 conf/asiacrypt/2003 ASIACRYPT db/conf/asiacrypt/asiacrypt2003.html#SatoTTT03